K2M 10-Q 8 Nov 18 2018 Q3 Quarterly report Financial data

DOCUMENT AND ENTITY INFORMATION

DOCUMENT AND ENTITY INFORMATION - shares	9 Months Ended
	Sep. 30, 2018	Oct. 30, 2018
Entity [Abstract]
Entity Registrant Name	K2M Group Holdings, Inc.
Entity Central Index Key	1,499,807
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Common Stock, Shares Outstanding		43,737,010

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 55,631	$ 23,964
Accounts receivable, net	54,053	50,474
Inventory, net	85,294	71,424
Prepaid expenses and other current assets	6,551	7,842
Total current assets	201,529	153,704
Property, plant and equipment, net	46,401	49,200
Surgical instruments, net	30,079	26,250
Goodwill	121,814	121,814
Intangible assets, net	18,988	18,899
Other assets, net	3,060	3,260
Total assets	421,871	373,127
Current liabilities:
Current maturities under capital lease obligation	1,241	1,122
Accounts payable	27,663	20,495
Accrued expenses	20,968	22,233
Accrued payroll liabilities	15,066	10,214
Total current liabilities	64,938	54,064
Convertible senior notes	93,016	39,176
Capital lease obligation, net of current maturities	32,863	33,812
Deferred income taxes, net	672	3,360
Other liabilities	353	316
Total liabilities	191,842	130,728
Commitments and contingencies
Stockholders’ equity:
Common stock, $0.001 par value, 750,000,000 shares authorized; 43,774,023 and 43,389,576 shares issued and 43,734,131 and 43,373,611 shares outstanding, respectively	44	43
Additional paid-in capital	518,572	491,012
Accumulated deficit	(287,226)	(249,221)
Accumulated other comprehensive (loss) income	(686)	876
Treasury stock, at cost, 39,892 and 15,965 shares, respectively	(675)	(311)
Total stockholders’ equity	230,029	242,399
Total liabilities and stockholders’ equity	$ 421,871	$ 373,127

CONSOLIDATED BALANCE SHEETS (Un

CONSOLIDATED BALANCE SHEETS (Unaudited) (Parenthetical) - $ / shares	Sep. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Common stock, par value per share (in usd per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	750,000,000	750,000,000
Common stock, shares issued (in shares)	43,774,023	43,389,576
Common stock, shares outstanding (in shares)	43,734,131	43,373,611
Treasury stock, (in shares)	39,892	15,965

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Revenue	$ 71,359	$ 62,653	$ 212,815	$ 190,230
Cost of revenue	25,755	20,425	75,798	64,426
Gross profit	45,604	42,228	137,017	125,804
Operating expenses:
Research and development	5,658	5,360	17,781	16,170
Sales and marketing	34,474	29,557	103,623	91,273
General and administrative	18,248	14,659	48,802	42,937
Total operating expenses	58,380	49,576	170,206	150,380
Loss from operations	(12,776)	(7,348)	(33,189)	(24,576)
Other expense, net:
Foreign currency transaction (loss) gain	(74)	671	(552)	1,518
Interest expense	(2,750)	(1,748)	(6,615)	(5,211)
Total other expense, net	(2,824)	(1,077)	(7,167)	(3,693)
Loss before income taxes	(15,600)	(8,425)	(40,356)	(28,269)
Income tax expense (benefit)	213	40	(2,351)	128
Net loss	$ (15,813)	$ (8,465)	$ (38,005)	$ (28,397)
Basic and diluted (in dollars per share)	$ (0.36)	$ (0.20)	$ (0.88)	$ (0.67)
Weighted average common shares outstanding:
Basic and diluted (in shares)	43,345,856	43,009,015	43,209,187	42,627,985

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net loss	$ (15,813)	$ (8,465)	$ (38,005)	$ (28,397)
Other comprehensive (loss) income:
Foreign currency translation adjustment	(850)	853	(1,562)	2,421
Other comprehensive (loss) income	(850)	853	(1,562)	2,421
Comprehensive loss	$ (16,663)	$ (7,612)	$ (39,567)	$ (25,976)

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS’ EQUITY (Unaudited) - 9 months ended Sep. 30, 2018 - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss	Treasury Stock
Beginning Balance (in shares) at Dec. 31, 2017	43,373,611	43,389,576				15,965
Beginning Balance at Dec. 31, 2017	$ 242,399	$ 43	$ 491,012	$ (249,221)	$ 876	$ (311)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(38,005)			(38,005)
Other comprehensive loss	(1,562)				(1,562)
Stock-based compensation	4,852		4,852
2018 convertible senior notes due 2025, equity conversion option	21,171		21,171
2018 convertible senior notes due 2025, issuance costs allocated to equity	(1,006)		(1,006)
Treasury stock (in shares)						23,927
Treasury stock	(364)					$ (364)
Issuances and exercise of stock-based compensation plans, net of tax (in shares)		384,447				0
Issuances and exercise of stock-based compensation plans, net of tax	$ 2,544	$ 1	2,543			$ 0
Ending Balance (in shares) at Sep. 30, 2018	43,734,131	43,774,023				39,892
Ending Balance at Sep. 30, 2018	$ 230,029	$ 44	$ 518,572	$ (287,226)	$ (686)	$ (675)

CONDENSED CONSOLIDATED STATEM_4

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Operating activities
Net loss	$ (38,005)	$ (28,397)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	17,251	21,424
Provision for inventory reserves	3,856	3,187
Provision for allowance for doubtful accounts	(750)	196
Stock-based compensation expense	4,852	4,322
Accretion of discounts and amortization of issuance costs of Convertible Notes	2,570	1,748
Deferred income taxes	(2,688)	0
Other	54	(14)
Changes in operating assets and liabilities:
Accounts receivable	(8,870)	2,444
Inventory	(16,992)	(9,510)
Prepaid expenses and other assets	1,905	(8,200)
Accounts payable, accrued expenses, and accrued payroll liabilities	12,159	4,092
Net cash used in operating activities	(24,658)	(8,708)
Investing activities
Purchases of surgical instruments	(13,343)	(7,199)
Purchases of property, plant and equipment	(2,520)	(3,242)
Purchase of intangible assets	0	(1,050)
Net cash used in investing activities	(15,863)	(11,491)
Financing activities
Borrowings on bank line of credit	18,000	0
Payments on bank line of credit	18,000	0
Payments under capital lease	(829)	(719)
Proceeds from issuances of 2018 convertible senior notes due 2025, net of issuance costs	71,452	0
Issuances and exercise of stock-based compensation plans, net of income tax	2,180	8,781
Net cash provided by financing activities	72,803	8,062
Effect of exchange rate changes on cash and cash equivalents	(615)	567
Net change in cash and cash equivalents	31,667	(11,570)
Cash and cash equivalents at beginning of period	23,964	45,511
Cash and cash equivalents at end of period	55,631	33,941
Significant non-cash investing activities
Assets acquired from business combination	5,236	0
Additions to property, plant and equipment	0	250
Reductions to property, plant and equipment from earned grant incentives	(395)	0
Cash paid for:
Income taxes	190	132
Interest	$ 2,342	$ 2,190

GENERAL AND SUMMARY OF SIGNIFIC

GENERAL AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
GENERAL AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	GENERAL AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES In this Quarterly Report on Form 10-Q, unless the context otherwise requires, references to “K2M,” “the Company,” “we,” “us” and “our,” refer to K2M Group Holdings, Inc. together with its consolidated subsidiaries. We are a global medical device provider of complex spine and minimally invasive solutions focused on achieving three-dimensional Total Body Balance. Since our inception, we have designed, developed and commercialized innovative complex spine and minimally invasive spine technologies and techniques used by spine surgeons to treat some of the most complicated spinal pathologies. K2M has leveraged these core competencies into Balance ACS™, a platform of products, services and research to help surgeons achieve three-dimensional spinal balance across the axial, coronal and sagittal planes, with the goal of supporting the full continuum of care to facilitate quality patient outcomes. The Balance ACS platform, in combination with our technologies, techniques and leadership in the 3D-printing of spinal devices, enable us to compete favorably in the global spinal surgery market. Unaudited Interim Results The accompanying condensed consolidated balance sheets as of September 30, 2018 and December 31, 2017 , the condensed consolidated statements of operations, the condensed consolidated statements of comprehensive loss for the three and nine months ended September 30, 2018 and 2017 , the condensed consolidated statement of changes in stockholders’ equity for the nine months ended September 30, 2018 , and the condensed consolidated statements of cash flows for the nine months ended September 30, 2018 and 2017 are unaudited. The unaudited interim consolidated financial statements have been prepared on the same basis of accounting as the annual consolidated financial statements and, in the opinion of management, reflect all adjustments, which include normal recurring adjustments, necessary to present fairly our financial position and results of operations and cash flows for the periods presented. The results for the three and nine months ended September 30, 2018 are not necessarily indicative of future results. All information as of September 30, 2018 and for the three and nine month periods ending September 30, 2018 and 2017 within these notes to the condensed consolidated financial statements is unaudited. Principles of Consolidation The accompanying consolidated financial statements include the accounts of the Company and all of its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. Use of Estimates The preparation of financial statements in conformity with generally accepted accounting principles in the United States, requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Revenue Recognition We adopted ASU 2014-09, Revenue from Contracts with Customers (“Topic 606”), with a date of initial adoption of January 1, 2018. In preparing for the adoption of the new standard, we reviewed our revenue generating activities, identified the performance obligations related to those activities, and determined the appropriate timing and measurement of revenue related to the performance obligations in accordance with the standard. We applied Topic 606 retrospectively to each period reported, however, based on the results of our evaluation, there were no changes to our historical condensed consolidated financial statements for the three and nine months ended September 30, 2018 as a result of this adoption. For revenue recognition arrangements that we determine are within the scope of Topic 606, we perform the following five steps: (i) identify the contract(s) with a customer, (ii) identify the performance obligations in the contract, (iii) determine the transaction price, (iv) allocate the transaction price to the performance obligations in the contract, and (v) recognize revenue when (or as) the entity satisfies a performance obligation. We only apply the five-step model to arrangements that meet the definition of a contract under Topic 606, including when it is probable that the entity will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of Topic 606, we evaluate the goods or services promised within each contract related performance obligation, and assess whether each promised good or service is distinct. We then recognize as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. In our direct markets, we make our products available to hospitals that purchase specific products for use in a surgery on a case by case basis. We recognize revenue upon the use of such products in the completion of a surgical procedure following a receipt of a delivered order confirming that such products have been used in such procedure. In certain instances, hospital customers may purchase our products in advance of a surgical procedure. Revenue from these transactions is recognized following the completion of our performance obligations associated with the transaction which are distinct under the contract which typically includes our shipment of the purchased products and transfer of control to the hospital customer at the point of delivery. International sales outside of our direct markets are contracted with international distributors, who then resell our products to their hospital customers. We recognize revenue upon completion of our performance obligations which includes shipment of the product to the distributor, who accepts title and control at the point of shipment. For these transactions, control transfers to the customer at the point of shipment. We recognize revenue at the transaction price that reflects the net consideration to which we expect to be entitled in exchange for our surgical products. If the transaction price includes variable consideration such as a discount, rebate, right of return or other sales incentives that reduce the transaction price such variable consideration is estimated when revenue is recognized based on the expected value approach. If taxes should be collected from customers relating to product sales and remitted to governmental authorities, they will be excluded from revenue. We expense incremental costs of obtaining a contract when incurred if the expected amortization period of the asset that we would have recognized is one year or less. We have determined that our contracts are short-term in nature and therefore no contract costs have been capitalized. Net Loss per Share Basic net loss per common share is determined by dividing the net loss allocable to common stockholders by the weighted average number of common shares outstanding during the periods presented, without consideration of common stock equivalents. Diluted loss per share is computed by dividing the net loss allocable to common stockholders by the weighted average number of shares of common stock and common stock equivalents outstanding for the period. The treasury stock method is used to determine the dilutive effect of our stock option grants. The if-converted method is used to determine the dilutive effect of the outstanding Convertible Notes. The weighted average shares used to calculate both basic and diluted loss per share are the same because common stock equivalents were excluded in the calculation of diluted loss per share because their effect would be anti-dilutive. Although included in our outstanding shares total as of September 30, 2018 and 2017 , shares of restricted stock are contingently issuable until their restrictions lapse and have been excluded from the weighted average shares outstanding. Foreign Currency Translation and Other Comprehensive Loss Our results of operations and cash flows are subject to fluctuations due to changes in foreign currency exchange rates. Our reporting currency is the U.S. dollar, which is also the functional currency of our domestic entities, while the functional currency of our foreign subsidiaries are the British Pound, Euro and Swiss Franc. Assets and liabilities denominated in foreign currencies are translated at the rate of exchange on the balance sheet date. Revenue and expenses are translated using the average exchange rate for the period. Net gains and losses resulting from the translation of foreign financial statements are recorded in other comprehensive income (loss). Net foreign currency gains or losses resulting from transactions in currencies other than the functional currencies are included in other expense, net on the consolidated statements of operations. Other Recently Adopted and Issued Accounting Pronouncements We adopted the following pronouncements effective January 1, 2018: In August 2016, the Financial Accounting Standards Board (“FASB”) issued ASU 2016-15, Statement of Cash Flows (Topic 230), Classification of Certain Cash Receipts and Cash Payments, which eliminates the diversity in practice related to the classification of certain cash receipts and payments for debt prepayment or extinguishment costs and other diverse practices. It also provides clarifications related to separately identifiable cash-flows and application of the predominance principle based on evaluating the source and nature of the underlying cash flows when determining whether it is a financing, investing, operating or a combination of cash flow classifications. The adoption of this ASU did not have an impact on our financial position, results of operations or cash flows. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230), Restricted Cash, which requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. ASU 2016-18 requires that these amounts be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. The adoption of this ASU did not have a material impact on our financial position, results of operations or cash flows. In January 2017, the FASB issued ASU 2017-04, Goodwill and Other (Topic 350), Simplifying the Test for Goodwill Impairment, which no longer requires an entity to measure a goodwill impairment loss by comparing the implied fair value to the carrying value of a reporting unit’s goodwill. Instead, any goodwill impairment charge will be recognized as the excess of a reporting unit’s carrying amount over its fair value, not to exceed the total amount of goodwill allocated to the reporting unit. In addition, an entity should consider income tax effects from any tax deductible goodwill on the carrying amount of the reporting unit when measuring the goodwill impairment loss, if applicable. This update did not affect the optional qualitative assessment of goodwill impairment. The adoption of this ASU did not have an impact on our financial position, results of operations or cash flows. In May 2017, the FASB issued ASU 2017-09, Compensation - Stock Compensation (Topic 718), Scope of modification accounting, which provides guidance about which changes to the terms of a share-based payment award should be accounted for as a modification. Under ASU 2017-09, a change to an award should be accounted for as a modification unless the fair value of the modified award is the same as the original award, inputs to the valuation technique used to value the award does not change, the vesting conditions do not change, and the classification as an equity or liability instrument do not change. The adoption of this ASU did not have an impact on our financial position, results of operations or cash flows. Accounting Pronouncements we will adopt at a later date: In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), which requires lessees to recognize the following for all leases (with the exception of short-term leases) at the commencement date: (i) a lease liability, which is a lessee’s obligation to make lease payments arising from a lease, measured on a discounted basis; and (ii) a right-of-use asset, which is an asset that represents the lessee’s right to use, or control the use of, a specified asset for the lease term. The revised guidance must be applied on a modified retrospective transition approach for leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements. Public companies will be required to comply with the guidance in 2019, and interim periods within that year. Early adoption is permitted for all entities. We are presently evaluating the impact of this guidance. In March 2018, the FASB issued ASU 2018-05, Income Taxes (Topic 740), Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin No. 118 (“SAB No. 118”), to state the income tax accounting implications of the Tax Cuts and Jobs Act (“New Tax Act”), which clarifies the measurement period time frame, changes in subsequent reporting periods and reporting requirements as a result of the New Tax Act of 2017. In accordance with SAB No. 118, a company must reflect the income tax effects of those aspects of the New Tax Act for which the accounting under ASC 740 is complete. To the extent that a company’s accounting for certain income tax effects of the New Tax Act is incomplete but it is able to determine a reasonable estimate, it must record a provisional estimate in the financial statements. If a company cannot determine a provisional estimate to be included in the financial statements, it should continue to apply ASC 740 on the basis of the provisions of the tax laws that were in effect immediately before the enactment of the New Tax Act. SAB No. 118 provides a measurement period that should not extend beyond one year and it begins in the period that includes the enactment date which was December 22, 2017. We have not completed the accounting for the income tax effects of certain elements of the New Tax Act, which will become effective in future years. When additional guidance and regulations enable us to finalize tax positions, we will reflect the impact of this ASU 2018-05 on the tax provision and deferred tax calculation as of December 31, 2018.

MERGER AGREEMENT WITH STRYKER C

MERGER AGREEMENT WITH STRYKER CORPORATION	9 Months Ended
	Sep. 30, 2018
Business Combinations [Abstract]
MERGER AGREEMENT WITH STRYKER CORPORATION	MERGER AGREEMENT WITH STRYKER CORPORATION On August 29, 2018, we, Stryker Corporation, a Michigan corporation (“Stryker”), and Austin Merger Sub Corp., a Delaware corporation and a wholly-owned subsidiary of Stryker (“Merger Sub”), entered into an Agreement and Plan of Merger (the “Merger Agreement”), pursuant to which, upon the terms and subject to the conditions set forth in the Merger Agreement, Merger Sub will merge with and into K2M (the “Merger”), with K2M continuing as the surviving corporation in the Merger and as a direct or indirect wholly owned subsidiary of Stryker. The boards of directors of each of K2M and Stryker have approved the Merger Agreement. Upon the terms and subject to the conditions of the Merger Agreement, at the effective time of the Merger, K2M stockholders will have the right to receive $ 27.50 per share in cash, without interest and less any applicable withholding taxes, for each share of K2M common stock that they own immediately prior to the effective time of the Merger (other than any shares held by us as treasury stock or held directly by Stryker or any subsidiary of Stryker (including Merger Sub)) and other than any shares owned by any stockholder who has properly exercised and perfected such holder’s demand for appraisal rights under Section 262 of the General Corporation Law of the State of Delaware and not effectively withdrawn or lost such holder’s rights to appraisal). In addition, the Merger Agreement provides that outstanding equity-based awards issued under our equity incentive plans will be treated as set forth below: • Stock Options . Each option to purchase shares of K2M common stock that is outstanding and unexercised immediately prior to the effective time of the Merger, whether vested or unvested, will be cancelled and converted into the right to receive a cash payment (without interest) equal to the product of (A) the excess, if any, of the merger consideration over the per share exercise price of such option, and (B) the number of shares of K2M common stock subject to such option as of the effective time of the Merger, net of any applicable withholding taxes required to be withheld by applicable law. Options with a per share exercise price equal to or exceeding the merger consideration will be cancelled without payment. • Restricted Stock Awards and Restricted Stock Unit Awards . Each K2M restricted stock award and K2M restricted stock unit award that is outstanding immediately prior to the effective time of the Merger, whether vested or unvested, will be cancelled and converted into the right to receive a cash payment (without interest) equal to the product of (A) the merger consideration and (B) the number of shares of K2M common stock underlying the award as of the effective time of the Merger, net of any applicable withholding taxes required to be withheld by applicable law. In addition, under the terms of our 4.125% convertible senior notes due 2036 which we issued in 2016 (the ‘‘2016 Convertible Notes’’) and our 3.00% convertible senior notes due 2025 which we issued in 2018 (the ‘‘2018 Convertible Notes’’ and, together with the 2016 Convertible Notes, the ‘‘Convertible Notes’’), from and after the effective time of the Merger, the Convertible Notes will no longer be convertible on the basis of K2M common stock and will instead be convertible into the cash consideration paid pursuant to the Merger. Pursuant to the terms of the respective indentures governing the Convertible Notes (the “Convertible Notes Indentures”), K2M and the trustee for each series of Convertible Notes will enter into supplemental indentures providing for such changes to the conversion right. The Convertible Notes will remain obligations of K2M following the Merger (until their conversion, repurchase, maturity or other cancellation). Under the terms of the Convertible Notes, the Merger will constitute both a Fundamental Change and Make-Whole Fundamental Change (in each case, as defined in the applicable Convertible Notes Indenture). As a result, holders of the Convertible Notes will be permitted to choose to (i) convert their Convertible Notes at a temporarily increased conversion rate, (ii) require K2M to buy back their Convertible Notes for a price equal to their principal amount plus accrued but unpaid interest to, but not including, the repurchase date or (iii) continue holding their Convertible Notes; provided, however, that holders of the 2018 Convertible Notes will not have the right to require K2M to buy back their 2018 Convertible Notes if the cash consideration such holder would receive upon conversion of their 2018 Convertible Notes would exceed what they would receive upon a repurchase of their 2018 Convertible Notes in connection with such Fundamental Change. If holders elect to convert their Convertible Notes in connection with the Merger, the conversion rate will be temporarily increased (as set forth in the applicable Convertible Notes Indenture) based upon (x) the date on which the Merger is consummated and (y) the per share merger consideration provided for in the Merger Agreement. K2M and Stryker have made customary representations, warranties and covenants in the Merger Agreement, including, among others, covenants that: (i) K2M will conduct its and its subsidiaries’ business in all material respects in the ordinary course of business and in a manner consistent with past practice during the interim period between the execution of the Merger Agreement and the effective time of the Merger, (ii) K2M will not, and will cause each of its subsidiaries not to, directly or indirectly engage in certain types of transactions or take certain actions during such period without the prior consent of Stryker, (iii) K2M will duly call, give notice of, convene and hold a special meeting of the K2M stockholders to consider and vote on a proposal to adopt the Merger Agreement, and (iv) unless there has been a Company Adverse Recommendation Change (as defined in the Merger Agreement) in compliance with the terms of the Merger Agreement, the Board of Directors of K2M will recommend adoption of the Merger Agreement by the stockholders of K2M. K2M has also made certain additional customary covenants, including, among others, covenants not to: (i) solicit or knowingly encourage any inquiries with respect to certain alternative business combination transactions or (ii) subject to certain exceptions designed to allow the Board of Directors of K2M to fulfill its fiduciary duties to K2M’s stockholders (described further below), engage in any discussions concerning, or provide any confidential information to, any person relating to certain alternative business combination transactions. Prior to the adoption of the Merger Agreement by our stockholders, (i) the Board of Directors of K2M may, in certain circumstances, effect a Company Adverse Recommendation Change (as defined in the Merger Agreement) and (ii) with respect to a Company Superior Proposal (as defined in the Merger Agreement), K2M may terminate the Merger Agreement to concurrently enter into a definitive agreement with respect to such Company Superior Proposal, provided that K2M must pay to Stryker a termination fee of $ 47,600 (the “Termination Fee”) prior to or concurrently with such termination. In the event that our Board of Directors effects a Company Adverse Recommendation Change permitted under the Merger Agreement (other than with respect to a Company Superior Proposal), Stryker may terminate the Merger Agreement and receive payment of the Termination Fee. In connection with any such action described in this paragraph, we must comply with certain notice and other specified conditions giving Stryker the opportunity to propose revisions to the terms of the transaction contemplated by the Merger Agreement during one or more match right periods and, if requested by Stryker, engaging in good faith negotiations with Stryker during such match right periods. K2M and Stryker have agreed to use their respective reasonable best efforts to consummate the Merger, including making filings with and seeking approvals from certain governmental entities necessary in connection with the Merger, including under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended (the “HSR Act”). In furtherance thereof, Stryker has agreed to accept certain restrictions on the assets of K2M and its subsidiaries, if and to the extent necessary to obtain such approvals, provided that Stryker will not be required to accept such restrictions if they would be material to the business of K2M and its subsidiaries taken as a whole. Consummation of the Merger is subject to certain customary conditions, including (i) the adoption of the Merger Agreement by the holders of a majority of the outstanding shares of our common stock (the “Stockholder Approval”), (ii) the absence of any law prohibiting or order preventing the consummation of the Merger, (iii) the expiration or termination of any applicable waiting period under the HSR Act and the receipt of authorization or consent under certain specified antitrust laws, (iv) the absence of a material adverse effect with respect to K2M, and (v) compliance in all material respects on the part of each of K2M and Stryker with such party’s covenants under the Merger Agreement. The obligation of each party to consummate the Merger is also conditioned upon the other party’s representations and warranties being true and correct (subject to certain materiality exceptions). The Merger Agreement contains certain termination rights for both K2M and Stryker, including (i) in the event that the Stockholder Approval is not obtained at a duly convened meeting of K2M stockholders, (ii) in the event that the Merger is not consummated on or before August 29, 2019 (the “ Outside Date ”), or (iii) in the event that a governmental authority has issued a final and non-appealable order that prohibits the Merger. The Merger Agreement also provides for certain additional termination rights and provides that, upon termination of the Merger Agreement in certain circumstances, including if the Merger Agreement is terminated by Stryker in the event the Board of Directors of K2M effects a Company Adverse Recommendation Change, or by K2M in accordance with, and subject to, the terms of the Merger Agreement to enter into a definitive agreement with respect to a Company Superior Proposal, K2M would be required to pay Stryker the Termination Fee. In no circumstance will K2M be obligated to pay more than one Termination Fee. The consummation of the Merger is not subject to any financing conditions. We anticipate that the total amount of funds necessary to consummate the Merger and the related transactions, not including fees and expenses, will be approximately $ 1,400,000 , including the estimated funds needed to (i) pay our stockholders the consideration due to them under the Merger Agreement; (ii) make payments in respect of outstanding K2M stock options, K2M restricted stock awards and K2M restricted stock unit awards pursuant to the Merger Agreement; and (iii) pay the outstanding net indebtedness of K2M, including the consideration payable to holders of the outstanding Convertible Notes. We understand that Stryker expects to use cash and other available funds to fund the Merger. In connection with the Merger, Piper Jaffray & Co. acted as financial advisor to K2M and will receive a fee from K2M, currently estimated to be approximately $ 21,400 . Such fee is contingent upon the consummation of the Merger, except for $ 1,000 of the fee which was paid to Piper Jaffray & Co. for rendering its fairness opinion to the K2M Board of Directors and is creditable against the total fee. We expensed the $ 1,000 opinion fee as a general and administrative expense in the three months ended September 30, 2018.

ACCOUNTS RECEIVABLE

ACCOUNTS RECEIVABLE	9 Months Ended
	Sep. 30, 2018
Receivables [Abstract]
ACCOUNTS RECEIVABLE	ACCOUNTS RECEIVABLE The following table summarizes accounts receivable, net of allowances: September 30, December 31, Accounts receivable $ 55,362 $ 52,820 Allowances (1,309 ) (2,346 ) Accounts receivable, net $ 54,053 $ 50,474

INVENTORY

INVENTORY	9 Months Ended
	Sep. 30, 2018
Inventory Disclosure [Abstract]
INVENTORY	INVENTORY The following table summarizes inventory, net of allowances: September 30, December 31, Finished goods $ 130,784 $ 109,342 Inventory allowances (45,490 ) (37,918 ) Inventory, net $ 85,294 $ 71,424 Inventory includes surgical instruments available for sale with a carrying value of $ 10,415 and $ 8,493 at September 30, 2018 and December 31, 2017 , respectively.

PREPAID EXPENSES AND OTHER CURR

PREPAID EXPENSES AND OTHER CURRENT ASSETS	9 Months Ended
	Sep. 30, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
PREPAIDS EXPENSES AND OTHER CURRENT ASSETS	PREPAID EXPENSES AND OTHER CURRENT ASSETS The following table summarizes prepaid expenses and other current assets: September 30, December 31, Prepaid expenses $ 2,882 $ 3,419 Other 3,669 4,423 Total $ 6,551 $ 7,842

PROPERTY, PLANT AND EQUIPMENT

PROPERTY, PLANT AND EQUIPMENT	9 Months Ended
	Sep. 30, 2018
Property, Plant and Equipment [Abstract]
PROPERTY, PLANT AND EQUIPMENT	PROPERTY, PLANT AND EQUIPMENT The following table summarizes property, plant and equipment: Estimated Useful Lives September 30, December 31, Buildings under capital lease 16 years $ 26,469 $ 26,469 Leasehold improvements, including property under capital lease 15 years 19,571 20,222 Equipment 3-5 years 4,718 4,290 Software 3 years 9,502 7,784 Computer equipment 3 years 1,276 1,165 Furniture and office equipment 5-7 years 3,854 3,823 Vehicles and other 3 years 859 878 Total 66,249 64,631 Less accumulated depreciation and amortization (19,848 ) (15,431 ) Property, plant and equipment, net $ 46,401 $ 49,200 Depreciation and amortization expense for property, plant and equipment was $ 1,566 and $ 1,522 for the three months ended September 30, 2018 and 2017 , respectively, and $ 4,663 and $ 4,327 for the nine months ended September 30, 2018 and 2017 , respectively. Included in this total is amortization expense for buildings and leasehold improvements under capital lease of $ 416 for each of the three months ended September 30, 2018 and 2017 and $ 1,247 for each of the nine months ended September 30, 2018 and 2017 . Interest expense on the capital lease obligation was $ 555 and $ 572 for the three months ended September 30, 2018 and 2017 , respectively and $ 1,678 and $ 1,728 for the nine months ended September 30, 2018 and 2017 , respectively.

SURGICAL INSTRUMENTS

SURGICAL INSTRUMENTS	9 Months Ended
	Sep. 30, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
SURGICAL INSTRUMENTS	SURGICAL INSTRUMENTS The following table summarizes surgical instruments: September 30, December 31, Surgical instruments $ 85,191 $ 72,018 Less accumulated depreciation and allowances (55,112 ) (45,768 ) Surgical instruments, net $ 30,079 $ 26,250 Depreciation and allowance expense for surgical instruments was $ 2,910 and $ 2,502 for the three months ended September 30, 2018 and 2017 , respectively, and $ 9,344 and $ 7,670 for the nine months ended September 30, 2018 and 2017 , respectively.

ACQUISITION

ACQUISITION	9 Months Ended
	Sep. 30, 2018
Business Combinations [Abstract]
ACQUISITION	ACQUISITION On May 1, 2018, we completed our acquisition of certain of the spine assets of Medcomtech, S.A., our distributor in Spain and Portugal. The assets acquired as part of the business combination consist of surgical implants and instrumentation, and customer contracts and relationships that will permit us to offer our products on a direct basis in these countries. In addition, we entered into an Agency and Services Agreement with Medcomtech, S.A. under which it will provide certain sales, market development and other support services to us. Based on the nature of the assets acquired and services to be provided by Medcomtech, S.A., we accounted for the acquisition as a business combination. A preliminary allocation of the fair value of the purchase consideration of $5,236 was allocated to the inventory, surgical instruments and customer relationships acquired, as determined by a third party valuation. The acquisition was funded through an exchange of net accounts receivable owed to us by Medcomtech, S.A. The initial accounting for the business combination has not yet been completed because the valuation of such assets has not been finalized. We expect to finalize our allocation of fair value prior to completion of the fiscal year 2018. Following the May 1, 2018 acquisition, we have recognized revenue from the use of our products in surgical procedures in Spain and Portugal consistent with our revenue recognition policies for our direct markets. Revenue recognized for the three months ended September 30, 2018 was approximately $ 2,299 compared to $ 1,000 for the three months ended September 30, 2017 . For the period May 1, 2018 through September 30, 2018, we recognized revenue of $ 4,644 compared to $ 2,799 from the comparable period in 2017.

INTANGIBLE ASSETS

INTANGIBLE ASSETS	9 Months Ended
	Sep. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
INTANGIBLE ASSETS	INTANGIBLE ASSETS Intangible assets, net comprise the following: September 30, 2018 Estimated Useful Lives Gross Accumulated Amortization Net Indefinite-lived intangible assets: Trademarks — $ 12,900 $ — $ 12,900 In-process research and development — 900 — 900 Other — 234 — 234 Subtotal 14,034 — 14,034 Subject to amortization Developed technology 4 - 6 years 62,000 (61,858 ) 142 Licensed technology 4 - 6 years 52,800 (52,624 ) 176 Customer relationships 4 - 10 years 30,280 (29,726 ) 554 Patents and other 2 - 17 years 6,078 (1,996 ) 4,082 Subtotal 151,158 (146,204 ) 4,954 Intangible assets, net $ 165,192 $ (146,204 ) $ 18,988 December 31, 2017 Estimated Useful Lives Gross Accumulated Amortization Net Indefinite-lived intangible assets: Trademarks — $ 12,900 $ — $ 12,900 In-process research and development — 900 — 900 Other — 242 — 242 Subtotal 14,042 — 14,042 Subject to amortization Developed technology 4 - 6 years 62,000 (61,808 ) 192 Licensed technology 4 - 6 years 52,800 (52,602 ) 198 Customer relationships 4 - 7 years 29,700 (29,700 ) — Patents and other 2 - 17 years 6,060 (1,593 ) 4,467 Subtotal 150,560 (145,703 ) 4,857 Intangible assets, net $ 164,602 $ (145,703 ) $ 18,899 Amortization expense of intangible assets was $ 174 and $ 1,836 for the three months ended September 30, 2018 and 2017 , respectively, and $ 501 and $ 6,581 for the nine months ended September 30, 2018 and 2017 , respectively. As described in “ Note 8 - Acquisition”, in May 2018, we acquired certain customer relationships of our former Spanish distributor in connection with our acquisition. These customer relationships will be amortized over an estimated useful life of 10 years. As of September 30, 2018 , the expected amortization expense for the remainder of 2018 and the following four years and thereafter is as follows: September 30, 2018 2018 $ 168 2019 662 2020 638 2021 576 2022 576 Thereafter 2,334 Total $ 4,954

ACCRUED EXPENSES

ACCRUED EXPENSES	9 Months Ended
	Sep. 30, 2018
Payables and Accruals [Abstract]
ACCRUED EXPENSES	ACCRUED EXPENSES Accrued expenses consist of the following: September 30, December 31, Accrued commissions $ 9,503 $ 9,495 Accrued royalties 3,333 3,489 Other 8,132 9,249 Total $ 20,968 $ 22,233

DEBT

DEBT	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
DEBT	DEBT Revolving Credit Facility We maintain a senior secured credit facilities credit agreement (as amended from time to time, the “Credit Agreement”) with Silicon Valley Bank and Comerica Bank as lenders, which is secured primarily by the assets of our operating subsidiaries in the United States and United Kingdom and expires on April 26, 2019. The credit facility consists of revolving credit facility of $ 55,000 , with a sub-facility for letters of credit in the aggregate availability amount of $ 10,000 and a swingline sub-facility in the aggregate availability amount of $ 5,000 . As of September 30, 2018 , we were in compliance with all the financial and other covenants of the credit facility. We had no outstanding borrowings on the revolving credit facility at September 30, 2018 . On June 8, 2018, we entered into an amendment to the Credit Agreement, which permits us to make additional cash distributions, as appropriate for interest and other payments under our 2016 Convertible Notes and our 2018 Convertible Notes. Under the Credit Agreement as amended, we are permitted to distribute up to $ 12,000 in aggregate to make interest payments on the Convertible Notes and up to $ 5,000 in aggregate to make cash payments in connection with any conversions of the Convertible Notes. We incurred interest expense of $ 0 and $ 31 related to the credit facility for the three months ended September 30, 2018 and 2017 , respectively, and $ 185 and $ 92 for the nine months ended September 30, 2018 and 2017 , respectively. The amortization expense of loan issuance fees was $ 24 and $ 31 for the three months ended September 30, 2018 and 2017 , respectively, and $ 65 and $ 92 for the nine months ended September 30, 2018 and 2017 , respectively. As of September 30, 2018 , we had $ 49,000 of unused borrowing capacity under the revolving credit facility, net of an issued but undrawn letter of credit for $ 6,000 , representing a security deposit on our corporate headquarters and operations facilities lease. Convertible Notes Convertible Notes consist of the following: September 30, December 31, September 30, December 31, Carrying Value Fair Value 2016 Covertible Notes $ 41,065 $ 39,176 $ 49,916 $ 45,294 2018 Convertible Notes 51,951 — 74,550 — Total $ 93,016 $ 39,176 $ 124,466 $ 45,294 In August 2016, we issued $ 50,000 aggregate principal amount of the 2016 Convertible Notes. The 2016 Convertible Notes are due August 15, 2036 unless earlier converted, redeemed or repurchased by us. The 2016 Convertible Notes pay interest at an annual rate of 4.125% , payable semi-annually in arrears on February 15 and August 15 of each year. In June 2018, we issued $ 75,000 aggregate principal amount of the 2018 Convertible Notes. The 2018 Convertible Notes are due June 30, 2025 unless earlier converted, redeemed or repurchased by us. The 2018 Convertible Notes pay interest at an annual rate of 3.00% , payable semi-annually in cash on June 30 and December 30 of each year beginning on December 30, 2018. We received net proceeds from the sale of the 2018 Convertible Notes of approximately $ 71,452 , after deducting underwriting discounts and commissions and estimated offering expenses of $ 3,564 . We used a portion of the proceeds to repay $ 18,000 of borrowings outstanding under the credit facility. The Convertible Notes are governed by, as applicable, (i) an indenture, dated as of August 11, 2016, between the Company and The Bank of New York Mellon, as trustee (the “Trustee”), relating to the 2016 Convertible Notes and (ii) an indenture, dated as of June 18, 2018 (the “2018 Indenture”), between the Company and the Trustee, relating to the 2018 Convertible Notes, each of which contain customary terms and covenants and events of default. The Convertible Notes are senior, unsecured obligations and are equal in right of payment with existing and future senior, unsecured indebtedness, senior in right of payment to our future indebtedness that is expressly subordinated to the Convertible Notes, and effectively subordinated to our existing and future secured indebtedness, to the extent of the value of the collateral securing that indebtedness. The Convertible Notes are structurally subordinated to all existing and future indebtedness and other liabilities, including trade payables, and preferred equity (to the extent we are not a holder thereof), if any, of our subsidiaries. Noteholders may convert their 2018 Convertible Notes at their option only under the following circumstances: (1) during any calendar quarter commencing after the calendar quarter ending on September 30, 2018 (and only during such calendar quarter), if the last reported sale price (as defined in the 2018 Indenture) per share of our common stock for at least 20 trading days (as defined in the 2018 Indenture), whether or not consecutive, during the period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter exceeds 130% of the conversion price (as defined in the 2018 Indenture) on such trading day; (2) during the five consecutive business days immediately after any five consecutive trading day period (such five consecutive trading day period, the “measurement period”) if the trading price (as defined in the 2018 Indenture) per $ 1,000 principal amount of 2018 Convertible Notes for each trading day of such measurement period was less than 98% of the product of the last reported sale price per share of our common stock and the applicable conversion rate on such trading day; (3) upon the occurrence of certain corporate events or distributions on our common stock, as described in the 2018 Indenture; (4) if we call the 2018 Convertible Notes for redemption; and (5) at any time from, and including, March 30, 2025 until the close of business on the second scheduled trading day immediately before the maturity date. We will settle conversions by paying or delivering, as applicable, cash, shares of our common stock or a combination of cash and shares of our common stock, at our election, based on the applicable conversion rate. The initial conversion rate is 35.2930 shares of common stock per $ 1,000 principal amount of the 2018 Convertible Notes, which represents an initial conversion price of approximately $ 28.33 per share of common stock, and is subject to adjustment upon certain events. Upon a “make-whole fundamental change” (as defined in the 2018 Indenture) or in connection with a notice of redemption, we will, in certain circumstances, increase the conversion rate for a holder that elects to convert its 2018 Convertible Notes in connection with such make-whole fundamental change or notice of redemption. The 2018 Convertible Notes are redeemable, in whole or in part, at our option at any time on or after July 5, 2022 if the last reported sale price per share of our common stock has been at least 130% of the conversion price then in effect for at least 20 trading days, whether or not consecutive, including the trading day immediately preceding the date on which we provide notice of redemption, during any 30 consecutive trading day period ending on, and including, the trading day immediately preceding the date on which we provide notice of redemption. The redemption price will be equal to the principal amount of the 2018 Convertible Notes to be redeemed, plus accrued and unpaid interest, if any, to but not including, the redemption date. Upon a “fundamental change”, noteholders may require us to repurchase their 2018 Convertible Notes in whole or in part for cash at a cash repurchase price equal to the principal amount of the 2018 Convertible Notes to be repurchased, plus accrued and unpaid interest, if any, to, but not including, the fundamental change repurchase date. Under the 2018 Indenture, if an event of default (as defined in the 2018 Indenture), other than certain bankruptcy and insolvency-related events of default with respect to the Company, occurs and is continuing, either the Trustee or the holders of at least 25% in aggregate principal amount of the outstanding 2018 Convertible Notes may declare the principal amount of and the accrued and unpaid interest on the outstanding 2018 Convertible Notes to be due and payable by notice to the Company. If an event of default arising out of certain events of bankruptcy or insolvency involving the Company occurs, the principal amount of the 2018 Convertible Notes and accrued and unpaid interest, if any, will automatically become due and payable. Additionally, the 2018 Indenture provides that the Company may not consolidate with or merge with or into, or sell, lease or otherwise transfer all or substantially all of the consolidated assets of the Company and its subsidiaries, taken as a whole, to another person, unless: (a) the resulting, surviving or transferee person (if not the Company) is a corporation, duly organized and existing under the laws of the United States, any state thereof or the District of Columbia that expressly assumes by a supplemental indenture all of the Company’s obligations under the 2018 Convertible Notes and the 2018 Indenture; and (b) immediately after giving effect to such transaction, no default or event of default (each as defined in the 2018 Indenture), has occurred and is continuing. Pursuant to ASC 470, we have bifurcated the debt and equity components of the 2018 Convertible Notes. The separation was performed by determining the fair value of a similar debt instrument without the associated equity component. That amount was then deducted from the initial gross proceeds of the 2018 Convertible Notes to arrive at a residual amount which was allocated to the conversion feature that is classified as equity. The difference between the principal amount of the 2018 Convertible Notes and estimated fair value of the liability component without the embedded equity component (representing the fair value of the embedded equity component) is recorded as a debt discount and an increase to additional paid in capital on the issuance date. The initial fair value of the indebtedness and the embedded conversion option of the 2018 Convertible Notes was $ 53,829 and $ 21,171 , respectively. The embedded conversion option was recorded in stockholders’ equity as debt discount, to be subsequently accreted to interest expense over the term of the 2018 Convertible Notes. Underwriting discounts and commissions and offering expenses for the 2018 Convertible Notes totaled approximately $ 3,564 and were allocated between the liability and the equity component in proportion to the allocation of proceeds and accounted for as debt issuance costs and equity issuance costs, respectively. As a result, $ 2,558 attributable to the indebtedness was recorded as a reduction to the carrying value of the 2018 Convertible Notes, which will be amortized as interest expense over the term of 2018 Convertible Notes and $ 1,006 attributable to the equity component was recorded a reduction to additional paid-in-capital in stockholders’ equity. See “ Note 2. Merger Agreement with Stryker Corporation” , for a description of the effect of the Merger on the Convertible Notes. Interest expense related to the 2016 Convertible Notes was $ 1,165 and $ 1,096 for the three months ended September 30, 2018 and 2017 , respectively, and $ 3,437 and $ 3,237 for the nine months ended September 30, 2018 and 2017 , respectively. These amounts included accretion expense of the debt discounts of $ 649 and $ 580 for the three months ended September 30, 2018 and 2017 , respectively, and $ 1,890 and $ 1,689 for the nine months ended September 30, 2018 and 2017 , respectively. Interest expense related to the 2018 Convertible Notes was $ 1,164 and $ 1,318 for the three and nine months ended September 30, 2018 , respectively. These amounts included accretion of the debt discounts and issuance costs of $ 601 and $ 680 for these periods.

STOCK-BASED COMPENSATION

STOCK-BASED COMPENSATION	9 Months Ended
	Sep. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
STOCK-BASED COMPENSATION	STOCK-BASED COMPENSATION As of September 30, 2018 , there was a total of 826,417 shares of common stock available for future grants under our stock purchase and equity award or incentive plans. The following table summarizes the stock-based compensation expense by financial statement line item and type of award: Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Cost of revenue $ 35 $ 29 $ 93 $ 108 Research and development 27 35 156 224 Sales and marketing 313 240 821 942 General and administrative 1,338 1,137 3,782 3,048 Total $ 1,713 $ 1,441 $ 4,852 $ 4,322 Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Stock options $ 802 $ 684 $ 2,349 $ 2,157 Restricted stock 692 594 1,955 1,353 Restricted stock units (“RSUs”) 145 81 336 487 Employee Stock Purchase Plan 74 82 212 325 Total $ 1,713 $ 1,441 $ 4,852 $ 4,322 The following table summarizes stock option plans activity: Shares Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term (years) Aggregate Intrinsic Value (1) Outstanding at December 31, 2017 3,165,387 $ 14.26 5.88 $ 15,567 Granted 385,333 23.38 Exercised (197,614 ) 10.61 Expired (23,990 ) 13.36 Forfeited (16,248 ) 18.66 Outstanding at September 30, 2018 3,312,868 $ 15.52 5.74 $ 39,287 Vested: At September 30, 2018 2,499,803 $ 13.57 4.70 $ 34,487 Expected to vest: At September 30, 2018 813,065 $ 21.51 1.97 $ 4,800 (1) Calculated using the fair market value per-share of our common stock as of September 30, 2018 and December 31, 2017 of $ 27.37 and $ 18.00 , respectively. A summary of restricted stock and RSU activity during the nine months ended September 30, 2018 is as follows: Restricted Stock Restricted Stock Units Number of Shares Weighted-Average Grant Date Fair Value Weighted-Average Remaining Term (years) Number of Shares Weighted-Average Grant Date Fair Value Weighted-Average Remaining Term (years) Non-vested at December 31, 2017 265,684 $ 19.46 2.03 46,247 $ 20.30 2.28 Vested (1) (123,052 ) 19.35 (15,917 ) 19.94 Granted 137,069 23.39 31,914 22.72 Forfeited (3,919 ) 17.70 — — Non-vested at September 30, 2018 275,782 $ 21.49 2.14 62,244 $ 21.63 2.18 Vested or expected to vest: At September 30, 2018 275,782 $ 21.49 2.14 62,244 $ 21.63 2.18 (1) Represents restricted stock and RSUs which vested in 2018. These shares and units were net settled, which resulted in the return of 16,009 shares, reflected as treasury shares and 3,542 units in lieu of withholding taxes for the nine months ended September 30, 2018 . See “ Note 2. Merger Agreement with Stryker Corporation ”, for a description of the effect of the Merger on equity-based awards.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	9 Months Ended
	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES Intellectual Property In the normal course of business, we enter into agreements to obtain the rights to certain intellectual property. In addition to royalty payments based on the sale of the underlying product incorporating such intellectual property, these agreements may require an up-front payment and/or milestone payments under certain conditions such as when regulatory approval is received, cumulative sales milestones or subscriber levels are achieved and other events. Typically, we have certain rights to cancel these agreements, with notice, without additional payments due other than the amount due at the time of cancellation. Royalties ranging from 2% to 10% of net sales may be due on the sale of related products under these agreements and some of the agreements contain minimum annual royalty amounts. As of September 30, 2018 , several of these agreements could require us to make additional payments should certain conditions be met in the future. Of these amounts, (i) up to $ 16,465 would be paid following the receipt of regulatory applications and approvals in the United States; (ii) up to $ 1,500 would be paid following attainment of certain subscriber levels as of July 2019 and July 2020, and (iii) up to $ 150 would be paid based on completion of software development in 2018 related to our Balance ACS platform. In addition, milestone payments of $ 500 , $ 2,000 and $ 4,000 are due upon the achievement of net sales of related products of $ 10,000 , $ 25,000 and $ 50,000 , respectively, related to one of these agreements. A royalty payment of 7% of net sales of related products may be due until such sales reach $ 20,000 .

RELATED PARTIES

RELATED PARTIES	9 Months Ended
	Sep. 30, 2018
Related Party Transactions [Abstract]
RELATED PARTIES	RELATED PARTIES In January 2017, pursuant to an underwritten public offering, our prior sponsor Welsh, Carson, Anderson & Stowe XI, L.P., and certain of its affiliates completed the sale of 4,000,000 shares of our common stock. We incurred transaction fees of approximately $ 225 which are reflected as general and administrative expenses for the nine months ended September 30, 2017 . We did not receive any proceeds from the sale of these shares.

INCOME TAXES

INCOME TAXES	9 Months Ended
	Sep. 30, 2018
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES The provision for income taxes includes both domestic and foreign minimum income taxes and changes in the valuation allowance. For the three months ended September 30, 2018 and 2017 , the income tax expense was $ 213 and $ 40 , respectively, resulting in an effective tax rate of (1.4)% and (0.5)% , respectively. For the nine months ended September 30, 2018 and 2017 , income tax (benefit) expense was $ (2,351) and $ 128 , respectively, resulting in an effective tax rate of 5.8% and (0.4)% , respectively. On December 22, 2017, the Tax Cuts and Jobs Act (H.R. 1) was enacted in the U.S. which provided for the indefinite carryforward of domestic net operating losses generated in tax years ending after December 31, 2017. As a result of this change, the domestic net operating losses we incurred from January 1, 2018 to June 30, 2018 were recognized in the three months ended June 30, 2018 to the extent that they are available to offset our indefinite-lived deferred tax liabilities. The effective tax rate for the nine months ended September 30, 2018 differs from the statutory rate due to minimum income taxes, permanent differences and changes in valuation allowances.

NET LOSS PER SHARE

NET LOSS PER SHARE	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
NET LOSS PER SHARE	NET LOSS PER SHARE The following table sets forth the computation of basic and diluted loss per share attributable to our common stockholders: Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Net loss per common share: Net loss $ (15,813 ) $ (8,465 ) $ (38,005 ) $ (28,397 ) Basic and diluted loss per common share: Basic and diluted weighted average common shares outstanding 43,345,856 43,009,015 43,209,187 42,627,985 Basic and diluted loss per common share $ (0.36 ) $ (0.20 ) $ (0.88 ) $ (0.67 ) The following outstanding securities, using the treasury stock method, were excluded from the above computations of net loss per share because their impact would be antidilutive due to the net losses during the nine months ended September 30, 2018 and 2017 : Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Stock options 3,312,868 3,197,577 3,312,868 3,197,577 Restricted stock 275,782 265,684 275,782 265,684 RSUs 62,244 44,092 62,244 44,092 As discussed in Note 11, we have $ 50,000 aggregate principal amount of 2016 Convertible Notes outstanding at September 30, 2018 and 2017 and $ 75,000 aggregate principal amount of 2018 Convertible Notes outstanding at September 30, 2018 . The Convertible Notes may be settled, at our election, in cash, shares of our common stock or combination of cash and shares of our common stock. For purposes of calculating the maximum dilutive impact, it is presumed that the Convertible Notes will be settled in common stock with the resulting potential common shares included in diluted earnings per share if the effect is more dilutive. The effect of the conversion of the Convertible Notes is excluded from the calculation of diluted loss per share because the net loss for the three and nine months ended September 30, 2018 and 2017 causes such securities to be antidilutive. The potential dilutive effect of these securities is shown in the table below: Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Conversion of 2016 Convertible Notes 2,512,082 2,707,852 2,512,082 2,707,852 Conversion of 2018 Convertible Notes 3,239,363 — 3,239,363 —

SEGMENT AND GEOGRAPHICAL CONCEN

SEGMENT AND GEOGRAPHICAL CONCENTRATION	9 Months Ended
	Sep. 30, 2018
Segment Reporting [Abstract]
SEGMENT AND GEOGRAPHICAL CONCENTRATION	SEGMENT AND GEOGRAPHICAL CONCENTRATION Operating segments are defined as components of an enterprise for which separate discrete financial information is available and evaluated regularly by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. We manage the business globally within one reporting segment. Segment information is consistent with how management reviews the business, makes investing and resource allocation decisions and assesses operating performance. Products are sold principally in the United States. International revenue represented 26.4% and 26.4% for the three and nine months ended September 30, 2018 , respectively, and no individual country represented 10% or greater of our consolidated revenue. One customer accounted for approximately 10.7% and 11.1% of total revenue for the three months ended September 30, 2018 and 2017 , respectively, and 12.2% and 10.5% for the nine months ended September 30, 2018 and 2017 , respectively. The following table represents total revenue by geographic area, based on the location of the customer: Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 United States $ 52,491 $ 48,474 $ 156,707 $ 145,456 International 18,868 14,179 56,108 44,774 Total $ 71,359 $ 62,653 $ 212,815 $ 190,230 We classify sales within the United States into three categories: complex spine pathologies, minimally invasive procedures and degenerative and other conditions. A significant portion of our international revenue is derived from our distributor partners who do not report their product usage at the surgeon or hospital level, which prevents us from providing a specific breakdown for our international revenue among the three product categories. These sales transactions are settled when we ship the product to the distributor. The following table represents domestic revenue by current procedure category: Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Complex spine $ 20,753 $ 20,047 $ 61,094 $ 57,525 Minimally invasive 8,507 7,694 25,568 24,351 Degenerative 23,231 20,733 70,045 63,580 52,491 48,474 156,707 145,456 International 18,868 14,179 56,108 44,774 Total $ 71,359 $ 62,653 $ 212,815 $ 190,230

GENERAL AND SUMMARY OF SIGNIF_2

GENERAL AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - (Policies)	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation The accompanying consolidated financial statements include the accounts of the Company and all of its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with generally accepted accounting principles in the United States, requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Revenue Recognition	Revenue Recognition We adopted ASU 2014-09, Revenue from Contracts with Customers (“Topic 606”), with a date of initial adoption of January 1, 2018. In preparing for the adoption of the new standard, we reviewed our revenue generating activities, identified the performance obligations related to those activities, and determined the appropriate timing and measurement of revenue related to the performance obligations in accordance with the standard. We applied Topic 606 retrospectively to each period reported, however, based on the results of our evaluation, there were no changes to our historical condensed consolidated financial statements for the three and nine months ended September 30, 2018 as a result of this adoption. For revenue recognition arrangements that we determine are within the scope of Topic 606, we perform the following five steps: (i) identify the contract(s) with a customer, (ii) identify the performance obligations in the contract, (iii) determine the transaction price, (iv) allocate the transaction price to the performance obligations in the contract, and (v) recognize revenue when (or as) the entity satisfies a performance obligation. We only apply the five-step model to arrangements that meet the definition of a contract under Topic 606, including when it is probable that the entity will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of Topic 606, we evaluate the goods or services promised within each contract related performance obligation, and assess whether each promised good or service is distinct. We then recognize as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. In our direct markets, we make our products available to hospitals that purchase specific products for use in a surgery on a case by case basis. We recognize revenue upon the use of such products in the completion of a surgical procedure following a receipt of a delivered order confirming that such products have been used in such procedure. In certain instances, hospital customers may purchase our products in advance of a surgical procedure. Revenue from these transactions is recognized following the completion of our performance obligations associated with the transaction which are distinct under the contract which typically includes our shipment of the purchased products and transfer of control to the hospital customer at the point of delivery. International sales outside of our direct markets are contracted with international distributors, who then resell our products to their hospital customers. We recognize revenue upon completion of our performance obligations which includes shipment of the product to the distributor, who accepts title and control at the point of shipment. For these transactions, control transfers to the customer at the point of shipment. We recognize revenue at the transaction price that reflects the net consideration to which we expect to be entitled in exchange for our surgical products. If the transaction price includes variable consideration such as a discount, rebate, right of return or other sales incentives that reduce the transaction price such variable consideration is estimated when revenue is recognized based on the expected value approach. If taxes should be collected from customers relating to product sales and remitted to governmental authorities, they will be excluded from revenue. We expense incremental costs of obtaining a contract when incurred if the expected amortization period of the asset that we would have recognized is one year or less. We have determined that our contracts are short-term in nature and therefore no contract costs have been capitalized.
Net Loss per Share	Net Loss per Share Basic net loss per common share is determined by dividing the net loss allocable to common stockholders by the weighted average number of common shares outstanding during the periods presented, without consideration of common stock equivalents. Diluted loss per share is computed by dividing the net loss allocable to common stockholders by the weighted average number of shares of common stock and common stock equivalents outstanding for the period. The treasury stock method is used to determine the dilutive effect of our stock option grants. The if-converted method is used to determine the dilutive effect of the outstanding Convertible Notes. The weighted average shares used to calculate both basic and diluted loss per share are the same because common stock equivalents were excluded in the calculation of diluted loss per share because their effect would be anti-dilutive. Although included in our outstanding shares total as of September 30, 2018 and 2017 , shares of restricted stock are contingently issuable until their restrictions lapse and have been excluded from the weighted average shares outstanding.
Foreign Currency Translation and Other Comprehensive Loss	Foreign Currency Translation and Other Comprehensive Loss Our results of operations and cash flows are subject to fluctuations due to changes in foreign currency exchange rates. Our reporting currency is the U.S. dollar, which is also the functional currency of our domestic entities, while the functional currency of our foreign subsidiaries are the British Pound, Euro and Swiss Franc. Assets and liabilities denominated in foreign currencies are translated at the rate of exchange on the balance sheet date. Revenue and expenses are translated using the average exchange rate for the period. Net gains and losses resulting from the translation of foreign financial statements are recorded in other comprehensive income (loss). Net foreign currency gains or losses resulting from transactions in currencies other than the functional currencies are included in other expense, net on the consolidated statements of operations.
Recent Accounting Pronouncements	Recently Adopted and Issued Accounting Pronouncements We adopted the following pronouncements effective January 1, 2018: In August 2016, the Financial Accounting Standards Board (“FASB”) issued ASU 2016-15, Statement of Cash Flows (Topic 230), Classification of Certain Cash Receipts and Cash Payments, which eliminates the diversity in practice related to the classification of certain cash receipts and payments for debt prepayment or extinguishment costs and other diverse practices. It also provides clarifications related to separately identifiable cash-flows and application of the predominance principle based on evaluating the source and nature of the underlying cash flows when determining whether it is a financing, investing, operating or a combination of cash flow classifications. The adoption of this ASU did not have an impact on our financial position, results of operations or cash flows. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230), Restricted Cash, which requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. ASU 2016-18 requires that these amounts be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. The adoption of this ASU did not have a material impact on our financial position, results of operations or cash flows. In January 2017, the FASB issued ASU 2017-04, Goodwill and Other (Topic 350), Simplifying the Test for Goodwill Impairment, which no longer requires an entity to measure a goodwill impairment loss by comparing the implied fair value to the carrying value of a reporting unit’s goodwill. Instead, any goodwill impairment charge will be recognized as the excess of a reporting unit’s carrying amount over its fair value, not to exceed the total amount of goodwill allocated to the reporting unit. In addition, an entity should consider income tax effects from any tax deductible goodwill on the carrying amount of the reporting unit when measuring the goodwill impairment loss, if applicable. This update did not affect the optional qualitative assessment of goodwill impairment. The adoption of this ASU did not have an impact on our financial position, results of operations or cash flows. In May 2017, the FASB issued ASU 2017-09, Compensation - Stock Compensation (Topic 718), Scope of modification accounting, which provides guidance about which changes to the terms of a share-based payment award should be accounted for as a modification. Under ASU 2017-09, a change to an award should be accounted for as a modification unless the fair value of the modified award is the same as the original award, inputs to the valuation technique used to value the award does not change, the vesting conditions do not change, and the classification as an equity or liability instrument do not change. The adoption of this ASU did not have an impact on our financial position, results of operations or cash flows. Accounting Pronouncements we will adopt at a later date: In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), which requires lessees to recognize the following for all leases (with the exception of short-term leases) at the commencement date: (i) a lease liability, which is a lessee’s obligation to make lease payments arising from a lease, measured on a discounted basis; and (ii) a right-of-use asset, which is an asset that represents the lessee’s right to use, or control the use of, a specified asset for the lease term. The revised guidance must be applied on a modified retrospective transition approach for leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements. Public companies will be required to comply with the guidance in 2019, and interim periods within that year. Early adoption is permitted for all entities. We are presently evaluating the impact of this guidance. In March 2018, the FASB issued ASU 2018-05, Income Taxes (Topic 740), Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin No. 118 (“SAB No. 118”), to state the income tax accounting implications of the Tax Cuts and Jobs Act (“New Tax Act”), which clarifies the measurement period time frame, changes in subsequent reporting periods and reporting requirements as a result of the New Tax Act of 2017. In accordance with SAB No. 118, a company must reflect the income tax effects of those aspects of the New Tax Act for which the accounting under ASC 740 is complete. To the extent that a company’s accounting for certain income tax effects of the New Tax Act is incomplete but it is able to determine a reasonable estimate, it must record a provisional estimate in the financial statements. If a company cannot determine a provisional estimate to be included in the financial statements, it should continue to apply ASC 740 on the basis of the provisions of the tax laws that were in effect immediately before the enactment of the New Tax Act. SAB No. 118 provides a measurement period that should not extend beyond one year and it begins in the period that includes the enactment date which was December 22, 2017. We have not completed the accounting for the income tax effects of certain elements of the New Tax Act, which will become effective in future years. When additional guidance and regulations enable us to finalize tax positions, we will reflect the impact of this ASU 2018-05 on the tax provision and deferred tax calculation as of December 31, 2018.

ACCOUNTS RECEIVABLE - (Tables)

ACCOUNTS RECEIVABLE - (Tables)	9 Months Ended
	Sep. 30, 2018
Receivables [Abstract]
Schedule of Accounts Receivable	The following table summarizes accounts receivable, net of allowances: September 30, December 31, Accounts receivable $ 55,362 $ 52,820 Allowances (1,309 ) (2,346 ) Accounts receivable, net $ 54,053 $ 50,474

INVENTORY - (Tables)

INVENTORY - (Tables)	9 Months Ended
	Sep. 30, 2018
Inventory Disclosure [Abstract]
Schedule of Current Inventory	The following table summarizes inventory, net of allowances: September 30, December 31, Finished goods $ 130,784 $ 109,342 Inventory allowances (45,490 ) (37,918 ) Inventory, net $ 85,294 $ 71,424

PREPAID EXPENSES AND OTHER CU_2

PREPAID EXPENSES AND OTHER CURRENT ASSETS (Tables)	9 Months Ended
	Sep. 30, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of prepaid expenses and other current assets	The following table summarizes prepaid expenses and other current assets: September 30, December 31, Prepaid expenses $ 2,882 $ 3,419 Other 3,669 4,423 Total $ 6,551 $ 7,842

PROPERTY, PLANT AND EQUIPMENT (

PROPERTY, PLANT AND EQUIPMENT (Tables)	9 Months Ended
	Sep. 30, 2018
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	The following table summarizes property, plant and equipment: Estimated Useful Lives September 30, December 31, Buildings under capital lease 16 years $ 26,469 $ 26,469 Leasehold improvements, including property under capital lease 15 years 19,571 20,222 Equipment 3-5 years 4,718 4,290 Software 3 years 9,502 7,784 Computer equipment 3 years 1,276 1,165 Furniture and office equipment 5-7 years 3,854 3,823 Vehicles and other 3 years 859 878 Total 66,249 64,631 Less accumulated depreciation and amortization (19,848 ) (15,431 ) Property, plant and equipment, net $ 46,401 $ 49,200

SURGICAL INSTRUMENTS - (Tables)

SURGICAL INSTRUMENTS - (Tables)	9 Months Ended
	Sep. 30, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of Surgical Instruments	The following table summarizes surgical instruments: September 30, December 31, Surgical instruments $ 85,191 $ 72,018 Less accumulated depreciation and allowances (55,112 ) (45,768 ) Surgical instruments, net $ 30,079 $ 26,250

INTANGIBLE ASSETS - (Tables)

INTANGIBLE ASSETS - (Tables)	9 Months Ended
	Sep. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Intangible Assets and Goodwill	Intangible assets, net comprise the following: September 30, 2018 Estimated Useful Lives Gross Accumulated Amortization Net Indefinite-lived intangible assets: Trademarks — $ 12,900 $ — $ 12,900 In-process research and development — 900 — 900 Other — 234 — 234 Subtotal 14,034 — 14,034 Subject to amortization Developed technology 4 - 6 years 62,000 (61,858 ) 142 Licensed technology 4 - 6 years 52,800 (52,624 ) 176 Customer relationships 4 - 10 years 30,280 (29,726 ) 554 Patents and other 2 - 17 years 6,078 (1,996 ) 4,082 Subtotal 151,158 (146,204 ) 4,954 Intangible assets, net $ 165,192 $ (146,204 ) $ 18,988 December 31, 2017 Estimated Useful Lives Gross Accumulated Amortization Net Indefinite-lived intangible assets: Trademarks — $ 12,900 $ — $ 12,900 In-process research and development — 900 — 900 Other — 242 — 242 Subtotal 14,042 — 14,042 Subject to amortization Developed technology 4 - 6 years 62,000 (61,808 ) 192 Licensed technology 4 - 6 years 52,800 (52,602 ) 198 Customer relationships 4 - 7 years 29,700 (29,700 ) — Patents and other 2 - 17 years 6,060 (1,593 ) 4,467 Subtotal 150,560 (145,703 ) 4,857 Intangible assets, net $ 164,602 $ (145,703 ) $ 18,899
Schedule of Expected Amortization Expense	As of September 30, 2018 , the expected amortization expense for the remainder of 2018 and the following four years and thereafter is as follows: September 30, 2018 2018 $ 168 2019 662 2020 638 2021 576 2022 576 Thereafter 2,334 Total $ 4,954

ACCRUED EXPENSES - (Tables)

ACCRUED EXPENSES - (Tables)	9 Months Ended
	Sep. 30, 2018
Payables and Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses consist of the following: September 30, December 31, Accrued commissions $ 9,503 $ 9,495 Accrued royalties 3,333 3,489 Other 8,132 9,249 Total $ 20,968 $ 22,233

DEBT (Tables)

DEBT (Tables)	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Convertible Notes	Convertible Notes consist of the following: September 30, December 31, September 30, December 31, Carrying Value Fair Value 2016 Covertible Notes $ 41,065 $ 39,176 $ 49,916 $ 45,294 2018 Convertible Notes 51,951 — 74,550 — Total $ 93,016 $ 39,176 $ 124,466 $ 45,294

STOCK-BASED COMPENSATION - (Tab

STOCK-BASED COMPENSATION - (Tables)	9 Months Ended
	Sep. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of stock-based compensation expense	The following table summarizes the stock-based compensation expense by financial statement line item and type of award: Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Cost of revenue $ 35 $ 29 $ 93 $ 108 Research and development 27 35 156 224 Sales and marketing 313 240 821 942 General and administrative 1,338 1,137 3,782 3,048 Total $ 1,713 $ 1,441 $ 4,852 $ 4,322 Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Stock options $ 802 $ 684 $ 2,349 $ 2,157 Restricted stock 692 594 1,955 1,353 Restricted stock units (“RSUs”) 145 81 336 487 Employee Stock Purchase Plan 74 82 212 325 Total $ 1,713 $ 1,441 $ 4,852 $ 4,322
Schedule of employee stock option plan activity	The following table summarizes stock option plans activity: Shares Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term (years) Aggregate Intrinsic Value (1) Outstanding at December 31, 2017 3,165,387 $ 14.26 5.88 $ 15,567 Granted 385,333 23.38 Exercised (197,614 ) 10.61 Expired (23,990 ) 13.36 Forfeited (16,248 ) 18.66 Outstanding at September 30, 2018 3,312,868 $ 15.52 5.74 $ 39,287 Vested: At September 30, 2018 2,499,803 $ 13.57 4.70 $ 34,487 Expected to vest: At September 30, 2018 813,065 $ 21.51 1.97 $ 4,800 (1) Calculated using the fair market value per-share of our common stock as of September 30, 2018 and December 31, 2017 of $ 27.37 and $ 18.00 , respectively.
Schedule of restricted stock and RSU activity	A summary of restricted stock and RSU activity during the nine months ended September 30, 2018 is as follows: Restricted Stock Restricted Stock Units Number of Shares Weighted-Average Grant Date Fair Value Weighted-Average Remaining Term (years) Number of Shares Weighted-Average Grant Date Fair Value Weighted-Average Remaining Term (years) Non-vested at December 31, 2017 265,684 $ 19.46 2.03 46,247 $ 20.30 2.28 Vested (1) (123,052 ) 19.35 (15,917 ) 19.94 Granted 137,069 23.39 31,914 22.72 Forfeited (3,919 ) 17.70 — — Non-vested at September 30, 2018 275,782 $ 21.49 2.14 62,244 $ 21.63 2.18 Vested or expected to vest: At September 30, 2018 275,782 $ 21.49 2.14 62,244 $ 21.63 2.18

NET LOSS PER SHARE - (Tables)

NET LOSS PER SHARE - (Tables)	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Schedule of Basic and Diluted Earnings Per Share	The following table sets forth the computation of basic and diluted loss per share attributable to our common stockholders: Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Net loss per common share: Net loss $ (15,813 ) $ (8,465 ) $ (38,005 ) $ (28,397 ) Basic and diluted loss per common share: Basic and diluted weighted average common shares outstanding 43,345,856 43,009,015 43,209,187 42,627,985 Basic and diluted loss per common share $ (0.36 ) $ (0.20 ) $ (0.88 ) $ (0.67 )
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	The following outstanding securities, using the treasury stock method, were excluded from the above computations of net loss per share because their impact would be antidilutive due to the net losses during the nine months ended September 30, 2018 and 2017 : Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Stock options 3,312,868 3,197,577 3,312,868 3,197,577 Restricted stock 275,782 265,684 275,782 265,684 RSUs 62,244 44,092 62,244 44,092 As discussed in Note 11, we have $ 50,000 aggregate principal amount of 2016 Convertible Notes outstanding at September 30, 2018 and 2017 and $ 75,000 aggregate principal amount of 2018 Convertible Notes outstanding at September 30, 2018 . The Convertible Notes may be settled, at our election, in cash, shares of our common stock or combination of cash and shares of our common stock. For purposes of calculating the maximum dilutive impact, it is presumed that the Convertible Notes will be settled in common stock with the resulting potential common shares included in diluted earnings per share if the effect is more dilutive. The effect of the conversion of the Convertible Notes is excluded from the calculation of diluted loss per share because the net loss for the three and nine months ended September 30, 2018 and 2017 causes such securities to be antidilutive. The potential dilutive effect of these securities is shown in the table below: Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Conversion of 2016 Convertible Notes 2,512,082 2,707,852 2,512,082 2,707,852 Conversion of 2018 Convertible Notes 3,239,363 — 3,239,363 —

SEGMENT AND GEOGRAPHICAL CONC_2

SEGMENT AND GEOGRAPHICAL CONCENTRATION - (Tables)	9 Months Ended
	Sep. 30, 2018
Segment Reporting [Abstract]
Schedule of Revenue by Geographic Area	The following table represents total revenue by geographic area, based on the location of the customer: Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 United States $ 52,491 $ 48,474 $ 156,707 $ 145,456 International 18,868 14,179 56,108 44,774 Total $ 71,359 $ 62,653 $ 212,815 $ 190,230
Schedule of Revenue by Products	The following table represents domestic revenue by current procedure category: Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Complex spine $ 20,753 $ 20,047 $ 61,094 $ 57,525 Minimally invasive 8,507 7,694 25,568 24,351 Degenerative 23,231 20,733 70,045 63,580 52,491 48,474 156,707 145,456 International 18,868 14,179 56,108 44,774 Total $ 71,359 $ 62,653 $ 212,815 $ 190,230

MERGER AGREEMENT WITH STRYKER_2

MERGER AGREEMENT WITH STRYKER CORPORATION (Details) - USD ($) $ / shares in Units, $ in Thousands	Aug. 29, 2018	Sep. 30, 2018	Jun. 18, 2018	Aug. 11, 2016
The Merger Agreement
Business Acquisition [Line Items]
Shares, right to receive, price per share (in dollars per share)	$ 27.50
Termination fee		$ 47,600
Consideration transferred		1,400,000
Estimated financial advisor fee	$ 21,400
Opinion fee	$ 1,000	$ 1,000
2016 Convertible Senior Notes | Convertible Senior Notes
Business Acquisition [Line Items]
Interest rate (as a percent)				4.125%
2018 Convertible Senior Notes | Convertible Senior Notes
Business Acquisition [Line Items]
Interest rate (as a percent)			3.00%

ACCOUNTS RECEIVABLE - (Details)

ACCOUNTS RECEIVABLE - (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Receivables [Abstract]
Accounts receivable	$ 55,362	$ 52,820
Allowances	(1,309)	(2,346)
Accounts receivable, net	$ 54,053	$ 50,474

INVENTORY - (Details)

INVENTORY - (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Inventory [Line Items]
Finished goods	$ 130,784	$ 109,342
Inventory allowances	(45,490)	(37,918)
Inventory, net	85,294	71,424
Surgical and Medical Instruments
Inventory [Line Items]
Inventory, net	$ 10,415	$ 8,493

PREPAID EXPENSES AND OTHER CU_3

PREPAID EXPENSES AND OTHER CURRENT ASSETS (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid expenses	$ 2,882	$ 3,419
Other	3,669	4,423
Total	$ 6,551	$ 7,842

PROPERTY, PLANT AND EQUIPMENT_2

PROPERTY, PLANT AND EQUIPMENT (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Total	$ 66,249	$ 64,631
Less accumulated depreciation and amortization	(19,848)	(15,431)
Property, plant and equipment, net	$ 46,401	49,200
Buildings under capital lease
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	16 years
Total	$ 26,469	26,469
Leasehold improvements, including property under capital lease
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	15 years
Total	$ 19,571	20,222
Equipment
Property, Plant and Equipment [Line Items]
Total	$ 4,718	4,290
Software
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	3 years
Total	$ 9,502	7,784
Computer equipment
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	3 years
Total	$ 1,276	1,165
Furniture and office equipment
Property, Plant and Equipment [Line Items]
Total	$ 3,854	3,823
Vehicles and other
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	3 years
Total	$ 859	$ 878
Minimum | Equipment
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	3 years
Minimum | Furniture and office equipment
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	5 years
Maximum | Equipment
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	5 years
Maximum | Furniture and office equipment
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	7 years

PROPERTY, PLANT AND EQUIPMENT -

PROPERTY, PLANT AND EQUIPMENT - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Property, Plant and Equipment [Abstract]
Depreciation	$ 1,566	$ 1,522	$ 4,663	$ 4,327
Amortization expense for capital lease	416	416	1,247	1,247
Interest expense on capital leases	$ 555	$ 572	$ 1,678	$ 1,728

SURGICAL INSTRUMENTS - (Details

SURGICAL INSTRUMENTS - (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Surgical instruments	$ 85,191		$ 85,191		$ 72,018
Less accumulated depreciation and allowances	(55,112)		(55,112)		(45,768)
Surgical instruments, net	30,079		30,079		$ 26,250
Depreciation and allowance expense	$ 2,910	$ 2,502	$ 9,344	$ 7,670

ACQUISITION (Details)

ACQUISITION (Details) - USD ($) $ in Thousands	3 Months Ended		5 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	May 01, 2018
Business Combinations [Abstract]
Purchase consideration allocated to inventory, surgical instruments and customer relationships acquired					$ 5,236
Revenue following acquisition	$ 2,299	$ 1,000	$ 4,644	$ 2,799

INTANGIBLE ASSETS - (Details)

INTANGIBLE ASSETS - (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	May 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Schedule of Intangible Asset by Major Class [Line Items]
Indefinite-lived intangible assets		$ 14,034		$ 14,034		$ 14,042
Subject to amortization, Gross		151,158		151,158		150,560
Accumulated Amortization		(146,204)		(146,204)		(145,703)
Total		4,954		4,954		4,857
Intangible Assets, Gross		165,192		165,192		164,602
Intangible Assets, Net		18,988		18,988		18,899
Amortization expense		174	$ 1,836	501	$ 6,581
Developed technology
Schedule of Intangible Asset by Major Class [Line Items]
Subject to amortization, Gross		62,000		62,000		62,000
Accumulated Amortization		(61,858)		(61,858)		(61,808)
Total		142		142		192
Licensed technology
Schedule of Intangible Asset by Major Class [Line Items]
Subject to amortization, Gross		52,800		52,800		52,800
Accumulated Amortization		(52,624)		(52,624)		(52,602)
Total		176		176		198
Customer relationships
Schedule of Intangible Asset by Major Class [Line Items]
Subject to amortization, Gross		30,280		30,280		29,700
Accumulated Amortization		(29,726)		(29,726)		(29,700)
Total		554		554		0
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	10 years
Patents and other
Schedule of Intangible Asset by Major Class [Line Items]
Subject to amortization, Gross		6,078		6,078		6,060
Accumulated Amortization		(1,996)		(1,996)		(1,593)
Total		4,082		4,082		4,467
Trademarks
Schedule of Intangible Asset by Major Class [Line Items]
Indefinite-lived intangible assets		12,900		12,900		12,900
In-process research and development
Schedule of Intangible Asset by Major Class [Line Items]
Indefinite-lived intangible assets		900		900		900
Other
Schedule of Intangible Asset by Major Class [Line Items]
Indefinite-lived intangible assets		$ 234		$ 234		$ 242
Minimum | Developed technology
Schedule of Intangible Asset by Major Class [Line Items]
Estimated Useful Lives				4 years		4 years
Minimum | Licensed technology
Schedule of Intangible Asset by Major Class [Line Items]
Estimated Useful Lives				4 years		4 years
Minimum | Customer relationships
Schedule of Intangible Asset by Major Class [Line Items]
Estimated Useful Lives				4 years		4 years
Minimum | Patents and other
Schedule of Intangible Asset by Major Class [Line Items]
Estimated Useful Lives				2 years		2 years
Maximum | Developed technology
Schedule of Intangible Asset by Major Class [Line Items]
Estimated Useful Lives				6 years		6 years
Maximum | Licensed technology
Schedule of Intangible Asset by Major Class [Line Items]
Estimated Useful Lives				6 years		6 years
Maximum | Customer relationships
Schedule of Intangible Asset by Major Class [Line Items]
Estimated Useful Lives				10 years		7 years
Maximum | Patents and other
Schedule of Intangible Asset by Major Class [Line Items]
Estimated Useful Lives				17 years		17 years

INTANGIBLE ASSETS Schedule of E

INTANGIBLE ASSETS Schedule of Expected Amortization Expense (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
2,017	$ 168
2,018	662
2,019	638
2,020	576
2,021	576
Thereafter	2,334
Total	$ 4,954	$ 4,857

ACCRUED EXPENSES - (Details)

ACCRUED EXPENSES - (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Payables and Accruals [Abstract]
Accrued commissions	$ 9,503	$ 9,495
Accrued royalties	3,333	3,489
Other	8,132	9,249
Total	$ 20,968	$ 22,233

DEBT - Narrative (Details)

DEBT - Narrative (Details)	Jun. 18, 2018USD ($)trading_day$ / shares	Jun. 16, 2018	Jun. 08, 2018USD ($)	Jun. 30, 2018USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)	Aug. 11, 2016USD ($)
Debt Instrument [Line Items]
Interest Expense					$ 2,750,000	$ 1,748,000	$ 6,615,000	$ 5,211,000
Letter of credit					6,000,000		6,000,000
Net proceeds							71,452,000	0
Repayments of Lines of Credit							18,000,000	0
2018 Convertible Senior Notes
Debt Instrument [Line Items]
Fair value of indebtedness	$ 53,829,000
Embedded conversion option	21,171,000
Underwriting discounts and commissions and offering expenses	$ 3,564,000
Line of Credit | June 2018 Amendment
Debt Instrument [Line Items]
Revolving credit facility									$ 5,000,000
Convertible Senior Notes | 2016 Convertible Senior Notes
Debt Instrument [Line Items]
Interest rate (as a percent)										4.125%
Principal amounts of debt										$ 50,000,000
Interest expense					1,165,000	1,096,000	3,437,000	3,237,000
Accretion of debt discount					649,000	580,000	1,890,000	1,689,000
Convertible Senior Notes | 2018 Convertible Senior Notes
Debt Instrument [Line Items]
Interest rate (as a percent)	3.00%
Principal amounts of debt	$ 75,000,000
Underwriting discounts and commissions and offering expenses	$ 3,564,000
Aggregate principal amount in an event of default	25.00%
Interest expense					1,164,000		1,318,000
Accretion of debt discount					601,000		680,000
Revolving Credit Facility
Debt Instrument [Line Items]
Amount outstanding					0		0
Unused borrowing capacity					49,000,000		49,000,000
Revolving Credit Facility | October 2015 Amendment
Debt Instrument [Line Items]
Revolving credit facility					55,000,000		55,000,000
Revolving Credit Facility | Credit Agreement 2012
Debt Instrument [Line Items]
Interest Expense					0	31,000	0	0
Repayments of Lines of Credit				$ 18,000,000
Revolving Credit Facility | June 2018 Amendment
Debt Instrument [Line Items]
Permitted distribution to make interest payments			$ 12,000,000
Revolving Credit Facility | Line of Credit | October 2015 Amendment
Debt Instrument [Line Items]
Revolving credit facility					10,000,000		10,000,000
Revolving Credit Facility | Line of Credit | Credit Agreement 2012
Debt Instrument [Line Items]
Amortization of Debt Issuance Costs					24,000	$ 31,000	65,000	$ 92,000
Revolving Credit Facility, Swing Line Loan | Line of Credit | Amended Credit Agreement 2012
Debt Instrument [Line Items]
Revolving credit facility					$ 5,000,000		5,000,000
Noteholder Conversion | Convertible Senior Notes | 2018 Convertible Senior Notes
Debt Instrument [Line Items]
Threshold trading days | trading_day	20
Consecutive trading days | trading_day	30
Threshold percentage of stock price trigger	130.00%
Measurement period	5 years
Maximum percentage of trading price trigger	98.00%
Conversion ratio		0.035293
Conversion price | $ / shares	$ 28.33
Company Redemption | Convertible Senior Notes | 2018 Convertible Senior Notes
Debt Instrument [Line Items]
Threshold trading days | trading_day	20
Consecutive trading days | trading_day	30
Threshold percentage of stock price trigger	130.00%
ASU 2015-03 | Long-term Debt | 2018 Convertible Senior Notes
Debt Instrument [Line Items]
Underwriting discounts and commissions and offering expenses	$ (2,558,000)
Additional Paid-in Capital
Debt Instrument [Line Items]
Reduction to APIC							$ (1,006,000)

DEBT - Convertible Debt (Detail

DEBT - Convertible Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Carrying Value
Debt Instrument [Line Items]
Convertible Notes	$ 93,016	$ 39,176
Carrying Value | Conversion of 2018 Convertible Notes
Debt Instrument [Line Items]
Convertible Notes	41,065	39,176
Carrying Value | Conversion of 2016 Convertible Notes
Debt Instrument [Line Items]
Convertible Notes	51,951	0
Fair Value
Debt Instrument [Line Items]
Convertible Notes	124,466	45,294
Fair Value | Conversion of 2018 Convertible Notes
Debt Instrument [Line Items]
Convertible Notes	49,916	45,294
Fair Value | Conversion of 2016 Convertible Notes
Debt Instrument [Line Items]
Convertible Notes	$ 74,550	$ 0

STOCK-BASED COMPENSATION - Narr

STOCK-BASED COMPENSATION - Narrative (Details)	Sep. 30, 2018shares
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	826,417

STOCK-BASED COMPENSATION - Allo

STOCK-BASED COMPENSATION - Allocation of Share-based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated stock-based compensation expense	$ 1,713	$ 1,441	$ 4,852	$ 4,322
Cost of revenue
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated stock-based compensation expense	35	29	93	108
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated stock-based compensation expense	27	35	156	224
Sales and marketing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated stock-based compensation expense	313	240	821	942
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated stock-based compensation expense	1,338	1,137	3,782	3,048
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated stock-based compensation expense	802	684	2,349	2,157
Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated stock-based compensation expense	692	594	1,955	1,353
Restricted stock units (“RSUs”)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated stock-based compensation expense	145	81	336	487
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated stock-based compensation expense	$ 74	$ 82	$ 212	$ 325

STOCK-BASED COMPENSATION - Summ

STOCK-BASED COMPENSATION - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands		9 Months Ended	12 Months Ended
		Sep. 30, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding Beginning Balance, Shares		3,165,387
Granted, Shares		385,333
Exercised, Shares		(197,614)
Expired, Shares		(23,990)
Forfeited, Shares		(16,248)
Outstanding Ending Balance, Shares		3,312,868	3,165,387
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Beginning, Weighted-Average Exercise Price (in usd per share)		$ 14.26
Granted, Weighted-Average Exercise Price (in usd per share)		23.38
Exercised, Weighted-Average Exercise Price (in usd per share)		10.61
Expired, Weighted-Average Exercise Price (in usd per share)		13.36
Forfeited, Weighted-Average Exercise Price (in usd per share)		18.66
Ending, Weighted-Average Exercise Price (in usd per share)		$ 15.52	$ 14.26
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Outstanding, Weighted- Average Remaining Contractual Term (years)		5 years 8 months 26 days	5 years 10 months 17 days
Outstanding, Aggregate Intrinsic Value	[1]	$ 15,567
Outstanding, Aggregate Intrinsic Value	[1]	$ 39,287	$ 15,567
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested [Abstract]
Vested, shares		2,499,803
Vested, Weighted-Average Exercise Price (in usd per share)		$ 13.57
Vested, Weighted-Average Remaining Contractual Term (years)		4 years 8 months 12 days
Vested, Aggregate Intrinsic Value		$ 34,487
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest [Abstract]
Vested or expected to vest, shares		813,065
Vested or expected to vest, Weighted-Average Exercise Price (in usd per share)		$ 21.51
Vested or expected to vest, Weighted-Average Remaining Contractual Term (years)		1 year 11 months 19 days
Vested or expected to vest, Aggregate Intrinsic Value	[1]	$ 4,800
Fair value valuation, estimated fair market value of stock (in dollars per share)		$ 27.37	$ 18
[1]	Calculated using the fair market value per-share of our common stock as of September 30, 2018 and December 31, 2017 of $27.37 and $18.00, respectively.

STOCK-BASED COMPENSATION - RSU

STOCK-BASED COMPENSATION - RSU and restricted stock table (Details) - $ / shares	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Paid for Tax Withholding for Share Based Compensation	16,009
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding Beginning Balance, Shares	265,684
Vested (in shares)	(123,052)
Granted (in shares)	137,069
Forfeited (in shares)	3,919
Outstanding Ending Balance, Shares	275,782	265,684
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Beginning, Weighted-Average Exercise Price (in usd per share)	$ 19.46
Vested, Weighted-Average Exercise Price (in usd per share)	19.35
Granted, Weighted-Average Exercise Price (in usd per share)	23.39
Forfeited, Weighted-Average Exercise Price (in usd per share)	17.70
Ending, Weighted-Average Exercise Price (in usd per share)	$ 21.49	$ 19.46
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Outstanding, Weighted Average Remaining Contractual Terms	2 years 1 month 20 days	2 years 10 days
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested or Expected to Vest, Number	275,782
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other Than Options, Vested and Expected to Vest, Outstanding, Weighted Average Grant Date Fair Value	$ 21.49
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other Than Options, Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term	2 years 1 month 20 days
Restricted Stock and Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Paid for Tax Withholding for Share Based Compensation	3,542
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding Beginning Balance, Shares	46,247
Vested (in shares)	(15,917)
Granted (in shares)	31,914
Forfeited (in shares)	0
Outstanding Ending Balance, Shares	62,244	46,247
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Beginning, Weighted-Average Exercise Price (in usd per share)	$ 20.30
Vested, Weighted-Average Exercise Price (in usd per share)	19.94
Granted, Weighted-Average Exercise Price (in usd per share)	22.72
Forfeited, Weighted-Average Exercise Price (in usd per share)	0
Ending, Weighted-Average Exercise Price (in usd per share)	$ 21.63	$ 20.30
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Outstanding, Weighted Average Remaining Contractual Terms	2 years 2 months 4 days	2 years 3 months 10 days
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested or Expected to Vest, Number	62,244
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other Than Options, Vested and Expected to Vest, Outstanding, Weighted Average Grant Date Fair Value	$ 21.63
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other Than Options, Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term	2 years 2 months 4 days

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - (Details) - USD ($)	1 Months Ended	9 Months Ended
	Nov. 30, 2011	Sep. 30, 2018
Licensed technology | Minimum
Long-term Purchase Commitment [Line Items]
Future maximum royalty payments		2.00%
Licensed technology | Maximum
Long-term Purchase Commitment [Line Items]
Future maximum royalty payments		10.00%
Patents and other
Long-term Purchase Commitment [Line Items]
Milestone payment one	$ 500,000
Milestone payment two	2,000,000
Milestone payment three	4,000,000
Milestone for milestone payment one	10,000,000
Milestone for milestone payment two	25,000,000
Milestone for milestone payment three	50,000,000
Patents and other | Maximum
Long-term Purchase Commitment [Line Items]
Contingent additional payment	$ 16,465,000
In-process research and development
Long-term Purchase Commitment [Line Items]
Future maximum royalty payments	7.00%
Other Commitment, Purchase Obligation, Related Product Sales, Royalty Payment Threshold	$ 20,000,000
Proprietary Technology Purchase Agreement, Payment Due Upon Subscriber Levels
Long-term Purchase Commitment [Line Items]
Contingent additional payment		$ 1,500,000
Proprietary Technology Purchase Agreement, Payment Due Upon Completion Of Software Development
Long-term Purchase Commitment [Line Items]
Contingent additional payment		$ 0

RELATED PARTIES (Details)

RELATED PARTIES (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2018	Dec. 31, 2017	Jan. 30, 2017
Related Party Transaction [Line Items]
Common stock, shares issued (in shares)		43,774,023	43,389,576
WCAS | Related Party Transaction, Sale of Stock
Related Party Transaction [Line Items]
Common stock, shares issued (in shares)				4,000,000
Underwriting commissions and transaction fees	$ 225

INCOME TAXES - (Details)

INCOME TAXES - (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Income tax (benefit) expense	$ 213	$ 40	$ (2,351)	$ 128
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent	(1.40%)	(0.50%)	5.80%	(0.40%)

NET LOSS PER SHARE - (Details)

NET LOSS PER SHARE - (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net loss	$ (15,813)	$ (8,465)	$ (38,005)	$ (28,397)
Basic and diluted weighted average common shares outstanding	43,345,856	43,009,015	43,209,187	42,627,985
Basic and diluted loss per common share (in dollars per share)	$ (0.36)	$ (0.20)	$ (0.88)	$ (0.67)

NET LOSS PER SHARE - Antidiluti

NET LOSS PER SHARE - Antidilutive Shares (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jun. 18, 2018	Aug. 11, 2016
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Earnings Per Share (in shares)	3,312,868	3,197,577	3,312,868	3,197,577
Restricted stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Earnings Per Share (in shares)	275,782	265,684	275,782	265,684
Restricted stock units (“RSUs”)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Earnings Per Share (in shares)	62,244	44,092	62,244	44,092
Conversion of 2016 Convertible Notes | Convertible Senior Notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Earnings Per Share (in shares)	3,239,363	0	3,239,363	0
Conversion of 2018 Convertible Notes | Convertible Senior Notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Earnings Per Share (in shares)	2,512,082	2,707,852	2,512,082	2,707,852
Convertible Senior Notes | Conversion of 2016 Convertible Notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Principal amounts of debt					$ 75,000,000
Convertible Senior Notes | Conversion of 2018 Convertible Notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Principal amounts of debt						$ 50,000,000

SEGMENT AND GEOGRAPHICAL CONC_3

SEGMENT AND GEOGRAPHICAL CONCENTRATION - Narrative (Details) - Segment	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Number of reportable segments			1
Sales Revenue, Net | Geographic Concentration Risk | International
Segment Reporting Information [Line Items]
International revenue as a percentage of total revenue	26.40%		26.40%
Sales Revenue, Net | Geographic Concentration Risk | United States
Segment Reporting Information [Line Items]
International revenue as a percentage of total revenue			10.00%
One Customer | Sales Revenue, Net | Customer Concentration Risk
Segment Reporting Information [Line Items]
International revenue as a percentage of total revenue	10.70%	11.10%	12.20%	10.50%

SEGMENT AND GEOGRAPHICAL CONC_4

SEGMENT AND GEOGRAPHICAL CONCENTRATION - Revenues by Geographic Area (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Revenue	$ 71,359	$ 62,653	$ 212,815	$ 190,230
Sales Revenue, Net
Segment Reporting Information [Line Items]
Revenue	71,359	62,653	212,815	190,230
United States
Segment Reporting Information [Line Items]
Revenue	52,491	48,474	156,707	145,456
United States | Sales Revenue, Net
Segment Reporting Information [Line Items]
Revenue	52,491	48,474	156,707	145,456
International | Sales Revenue, Net
Segment Reporting Information [Line Items]
Revenue	$ 18,868	$ 14,179	$ 56,108	$ 44,774

SEGMENT AND GEOGRAPHICAL CONC_5

SEGMENT AND GEOGRAPHICAL CONCENTRATION - Revenues by Product (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue from External Customer [Line Items]
Revenue	$ 71,359	$ 62,653	$ 212,815	$ 190,230
United States
Revenue from External Customer [Line Items]
Revenue	52,491	48,474	156,707	145,456
United States | Complex spine
Revenue from External Customer [Line Items]
Revenue	20,753	20,047	61,094	57,525
United States | Minimally invasive
Revenue from External Customer [Line Items]
Revenue	8,507	7,694	25,568	24,351
United States | Degenerative
Revenue from External Customer [Line Items]
Revenue	23,231	20,733	70,045	63,580
International
Revenue from External Customer [Line Items]
Revenue	$ 18,868	$ 14,179	$ 56,108	$ 44,774