Summary of Significant Accounting Policies | Summary of Significant Accounting Policies Basis of Presentation and Principles of Consolidation The accompanying consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”). The consolidated financial statements include the Company's accounts, as well as those of the Company's wholly-owned international subsidiaries. All inter-company accounts and transactions have been eliminated. Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of revenue and expenses during the reporting period . Significant accounting estimates and management judgments reflected in the consolidated financial statements primarily includes the fair value of stock options. Estimates are based on historical experience, where applicable and other assumptions believed to be reasonable by the management. Actual results could differ from those estimates. Segments The Company's chief operating decision makers are the Chief Executive Officer (“CEO”) and Chief Financial Officer (“CFO”). The CEO and the CFO review financial information presented on a consolidated basis, accompanied by information about revenue by geographic region, for purposes of evaluating financial performance. The Company has one business activity and there are no segment managers who are held accountable for operations, operating results or plans for levels or components below the consolidated unit level. Accordingly, the Company has determined that it has a single reportable and operating segment structure. The Company derives substantially all of its revenue from sales to customers in the U.S. Revenue by geography is based on billing address of the customer. International revenue accounted for less than 10% of the total revenue during the periods presented. Long-lived assets held outside the U.S. are immaterial. Following table summarizes the Company's revenue by geography: Year Ended December 31, 2021 2020 (in thousands) United States $ 82,739 $ 68,118 International 7,413 5,269 $ 90,152 $ 73,387 Foreign Currency The Company’s foreign subsidiaries use local currency as their functional currency. Assets and liabilities are translated at exchange rates prevailing at the balance sheet dates. Revenue, costs and expenses are translated into U.S. dollars using average exchange rates for the period. Gains and losses from foreign currency translation are recorded as a component of accumulated other comprehensive income (loss). Gains and losses from foreign currency transactions are recognized as a component of other income (expense), net. Concentration of Credit Risk Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash and marketable securities. The Company’s cash and marketable securities are deposited with financial institutions in the U.S. and in Europe. The majority of the Company’s cash and marketable securities are deposited with a single financial institution in the U.S. Deposits in this institution exceed the amount of insurance provided on such deposits. The Company has not experienced any net losses on its deposits of cash and marketable securities. The Company’s revenue and accounts receivable are spread across a large number of customers, primarily in the U.S., and no customer accounts for more than 10% of total revenue or gross accounts receivable in any period presented. Fair Value of Financial Instruments Carrying amounts of certain of the Company’s financial instruments, including cash equivalents, accounts receivable, accounts payable, and accrued liabilities, approximate fair value due to their relatively short maturities and market interest rates, if applicable. The Company's marketable securities are classified as Level 1 or Level 2 of the fair value hierarchy as defined below. The carrying value of the Company’s long-term debt also approximates fair value based on management’s estimation that a current interest rate would not differ materially from the stated rate. The Company discloses and recognizes the fair value of its assets and liabilities using a hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. Fair value is an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, a three-tier value hierarchy has been established, which prioritizes the inputs used in measuring fair value as follows: Level 1: Quoted prices (unadjusted) in active market that are accessible at measurement date for assets or liabilities. The fair value hierarchy gives the highest priority to Level 1 inputs. Level 2: Observable prices that are based on inputs not quoted on active markets, but corroborated by market data. Level 3: Unobservable inputs are used when little or no market data is available. The fair value hierarchy gives the lowest priority to Level 3 inputs. Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires management to make judgments and considers factors specific to the asset or liability. Cash and Cash Equivalents The Company considers all highly liquid investments with remaining maturities at the date of purchase of three months or less to be cash equivalents. Marketable Securities The Company's marketable securities primarily consist of investments in money market funds, U.S. treasury securities, corporate bonds and commercial paper. All of the Company's marketable securities are available-for-sale and are classified based on their maturities. Marketable securities with remaining maturities at the date of purchase of three months or less are classified as cash equivalents. Short term investments are securities that original or remaining maturity is greater than three months and not more than twelve months. Long-term investments are securities that original or remaining maturity is more than twelve months. All marketable securities are recorded at their estimated fair value. When the fair value of a security is below its amortized cost, the amortized cost will be reduced to its fair value if it is more likely than not that the Company will be required to sell the potentially impaired security before recovery of its amortized cost basis, or the Company has the intention to sell the security. If neither of these conditions are met, the Company determines whether the impairment is due to credit losses by comparing the present value of the expected cash flows of the security with its amortized cost basis. The amount of impairment recognized is limited to the excess of the amortized cost over the fair value of the security. An allowance for credit losses for the excess of amortized cost over the expected cash flows is recorded in other income, net in the consolidated statements of operations. Impairment losses that are not credit-related are included in accumulated other comprehensive income (loss) in stockholders’ equity. Accounts Receivable and Allowance for Credit Losses Trade accounts receivable are recorded at the invoiced amount, net of allowances for credit losses for any potential uncollectible amounts. The allowance for credit losses is based on our assessment of the collectability of accounts. Management regularly reviews the adequacy of the allowance for credit losses on a collective basis by considering the age of each outstanding invoice, each customer’s expected ability to pay and collection history, current market conditions, and reasonable and supportable forecasts of future economic conditions to determine whether the allowance is appropriate. Accounts receivable are written-off and charged against an allowance for credit losses when the Company has exhausted collection efforts without success. For the years ended December 31, 2021 and 2020, the allowance for credit losses activity was not significant. The movement in the allowance for credit losses was as follows: Year ended December 31, 2021 2020 (in thousands) Balance at beginning of year $ 263 $ 238 Provision 14 234 Write-offs (13) (209) Balance at end of year $ 264 $ 263 Inventory Inventory is stated at lower of cost or net realizable value. The Company establishes the inventory basis by determining the cost based on standard costs approximating the purchase costs on a first-in, first-out basis. The excess and obsolete inventory is estimated based on future demand and market conditions. Inventory write-downs are charged to cost of goods sold. Property and Equipment Property and equipment are stated at cost less accumulated depreciation and amortization. All property and equipment is depreciated on a straight-line basis over the estimated useful lives of the assets, which are as follows: Computer and office equipment 3 – 5 years Machinery and equipment 3 – 5 years Furniture and fixtures 7 years Leasehold improvements are amortized over the lesser of their useful lives or the life of the lease. Upon sale or retirement of the assets, the cost and related accumulated depreciation are removed from the consolidated balance sheet and the resulting gain or loss is recognized in the consolidated statement of operations. Maintenance and repairs are charged to operations as incurred. Impairment of Long-Lived Assets The Company reviews long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of the assets (or asset group) may not be fully recoverable. Whenever events or changes in circumstances suggest that the carrying amount of long-lived assets may not be recoverable, the Company estimates the future cash flows expected to be generated by the assets (or asset group) from its use or eventual disposition. If the sum of the expected future cash flows is less than the carrying amount of those assets, the Company recognizes an impairment loss based on the excess of the carrying amount over the fair value of the assets. Significant management judgment is required in the grouping of long-lived assets and forecasts of future operating results that are used in the discounted cash flow method of valuation. Through December 31, 2021 and 2020, the Company has not experienced impairment losses on its long-lived assets. Leases The Company determines if an arrangement is a lease at inception. The classification of leases is evaluated at commencement and, as necessary, at modification. Operating leases are included in operating lease right-of-use assets and operating lease liabilities on the consolidated balance sheets. The Company does not have any material finance leases in any of the periods presented. Under Accounting Standards Update ("ASU") 2016-02, Leases Topic 842 ("Topic 842"), operating lease expense is recognized on a straight-line basis over the term of the lease. Variable lease payments are recognized as operating expenses in the period in which the obligation for those payments is incurred. Variable lease payments primarily include common area maintenance, utilities, real estate taxes and other operating costs that are passed on from the lessor in proportion to the space leased by the Company. The lease term represents the non-cancelable period of the lease. For certain leases, the Company has an option to extend the lease term. These renewal options are not considered in the remaining lease term unless it is reasonably certain that the Company will exercise such options. The Company elected certain practical expedients under Topic 842 which are: (i) to not record leases with an initial term of twelve months or less on the balance sheet; (ii) to combine the lease and non-lease components in determining the lease liabilities and right-of-use assets, and (iii) to carry forward prior conclusions about lease identification and classification. The Company’s lease contracts do not provide an implicit borrowing rate; hence the Company determined the incremental borrowing rate based on information available at lease commencement to determine the present value of lease liability. The Company determines its incremental borrowing rate based on the rate of interest that the Company would have to pay to borrow on a collateralized basis over a similar term, an amount equal to the lease payments in a similar economic environment. The Company uses its headquarters in the U.S. ("parent entity")’s incremental borrowing rates as the treasury operations are managed centrally by the parent entity. Revenue Recognition The Company’s revenue is derived from the sale of its products to medical groups and hospitals through its direct sales force and distributors throughout the U.S. and Europe. The Company adopted the revenue standard in accordance with ASC Topic 606, Revenue from Contracts with Customers (“ASC 606”) effective for the fiscal year ended December 31, 2019. Revenue is recognized when control is transferred to the customer, in an amount that reflects the consideration the Company expects to be entitled to in exchange for the goods or services. Under the revenue recognition standard, the Company applies the following five step approach: (1) identify the contract with a customer, (2) identify the performance obligations in the contract, (3) determine the transaction price, (4) allocate the transaction price to the performance obligations in the contract, and (5) recognize revenue when a performance obligation is satisfied. As it relates to product sales where the Company's sales representative delivers the product at the point of implantation at the hospital or medical facilities, the Company continues to recognize the revenue upon completion of the procedure and authorization by the customer, net of rebates and price discounts. This represents the majority of the Company's consolidated revenue. The Company also generates a small portion of revenue from the sale of products through distributors and to certain hospital or medical facilities where the products are ordered in advance of a procedure. The performance obligation is the delivery of the products and therefore, revenue is recognized upon shipment to the customers, net of rebates and price discounts. The Company accounts for rebates and price discounts as a reduction to revenue, calculated based on the terms agreed to with the customer. Historically, there had been no significant price discounts. Sales prices are specified in either the customer contract or agreed price list, which is executed prior to the transfer of control to the customer. For certain hospitals and medical facilities, the Company has agreements in place consists of either a master services agreement or an agreed price list, which defines the terms and conditions of the arrangement, including the pricing information, payment terms and pertinent aspects of the relationship between the parties. The Company also has agreements in place with its distributors, which include standard terms that do not allow for payment contingent on resale of the product, obtaining financing, or other terms that could impact the distributor’s payment obligation. The Company's standard payment terms are generally net 30 to 90 days. Shipping and Handling Costs Shipping and handling costs are treated as fulfillment costs, which are expensed as incurred and are included in cost of goods sold. Costs to Obtain Customer Contracts Sales commissions and related expenses are considered incremental and recoverable costs of acquiring customer contracts. The Company’s sales commissions paid to its sales representatives are generally based on the surgeries performed. The Company applied the practical expedient that permits an entity to expense the cost to obtain a contract as incurred when the expected amortization is one year or less. The period of benefit is concurrent with when the Company recognizes its revenue and as such, the Company recognizes sales commission as expense when incurred. Warranty The Company has a warranty program that provides a purchaser a one-time replacement of any iFuse implant at no additional cost for a revision procedure within a one-year period following the original procedure and is accounted for as a warranty accrual. The Company also provides a purchaser with a one-time credit equal to the purchase price paid for use on future purchases for any revision procedure within the one-year period following an original procedure where an implant is not required. The warranty is not priced or sold separately and is intended to safeguard the customer against defects and it does not provide incremental service to the customer. As such, it is considered an assurance type warranty and is not accounted as a service type warranty, which could represent a separate performance obligation. The Company accounts for these one-time credits as sales reserves and is included in accrued liabilities and other in the consolidated balance sheets. Sales and warranty reserves from the warranty program were immaterial as of December 31, 2021 and 2020. Research and Development Research and development costs are charged to operations as incurred and consist of costs incurred by the Company for the development of the Company’s product which primarily include: (1) employee-related expenses, including salaries, benefits, travel and non-cash stock-based compensation expense; (2) external research and development expenses; and (3) other expenses, which include direct and allocated expenses for facilities and other costs. Advertising Expenditures The cost of advertising is expensed as incurred and is included under sales and marketing expense in the consolidated statements of operations. Advertising expenses were $1.2 million and $0.3 million for the year ended December 31, 2021 and 2020, respectively. Loss Contingency The Company is subject to various potential loss contingencies arising in the ordinary course of business. From time to time, the Company may be involved in certain proceedings, legal actions and claims. Such matters are subject to many uncertainties, and the outcomes of these matters are not within the Company's control and may not be known for prolonged periods of time. In some actions, the claimants may seek damages, as well as other relief, including injunctions which may prohibit the Company to engage in certain activities, which, if granted, could require significant expenditures and/or result in lost revenues. The Company records a liability in the consolidated financial statements when a loss is known or considered probable and the amount can be reasonably estimated. If the reasonable estimate of a known or probable loss is a range, and no amount within the range is a better estimate than any other, the minimum amount of the range is accrued. If a loss is reasonably possible but not known or probable, and can be reasonably estimated, the estimated loss or range of loss is disclosed. In most cases, significant judgment is required to estimate the amount and timing of a loss to be recorded. Stock-Based Compensation The Company applies the fair value recognition provisions of stock-based compensation. Stock-based compensation expense is recognized over the requisite service period using the straight-line method and is based on the value of the portion of stock-based payment awards that is ultimately expected to vest. As such, the Company’s stock-based compensation is reduced for the estimated forfeitures at the date of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. The Company uses historical data to estimate pre-vesting forfeitures and record stock-based compensation expense only for those awards that are expected to vest. To the extent actual forfeitures differ from the estimates, the difference will be recorded as a cumulative adjustment in the period that the estimates are revised. The Company estimates the grant date fair value of stock options using the Black-Scholes option valuation model. The model requires management to make a number of assumptions including expected volatility, expected term, risk-free interest rate and expected dividends. A number of these assumptions are subjective, and their determination generally require judgment. • Expected Term - The expected term represents the period that the share-based awards are expected to be outstanding. The Company uses the simplified method to determine the expected term as permitted by the guidance since the Company has no sufficient historical exercise patterns to estimate the expected life. The simplified method is calculated as the average of the time to vesting and the contractual life of the options. • Expected Volatility - The expected volatility is measured using the historical daily changes in the market price of the Company's common stock over a period consistent with the expected term. • Risk-Free Interest Rate - The risk-free interest rate is based on the U.S. Treasury zero coupon issued in effect at the time of grant for periods corresponding with the expected term of the option. • Dividend Yield - The Company has not paid any dividends and has no current plans to pay dividends on its common stock. As such, the Company uses expected dividend yield of zero. The fair value of the restricted stock unit (“RSU”) grant is based on the market price of the Company’s common stock on the date of grant. Prior to the Company's initial public offering (“IPO”), the fair value of the shares of the Company's common stock has historically been determined by its Board of Directors since there were no public market information available for the Company's common stock. The estimated fair value of the Company's common stock was determined at each valuation date in accordance with the guidelines outlined in the American Institute of Certified Public Accountants Practice Aid, Valuation of Privately-Held-Company Equity Securities Issued as Compensation . Subsequent to its IPO, the Company uses the market closing price for its common stock as reported on the Nasdaq Global Market on the date of grant. Equity instruments issued to non-employees are recorded at their fair value on the measurement date and are subject to periodic adjustments as the underlying equity instruments vest. The Company believes that the estimated fair value of the stock options is more readily measurable than the fair value of the services received. Stock-based compensation related to stock options granted to non-employees is recognized as the stock options are earned. In the event the underlying terms of stock options are modified on which stock-based compensation was granted, additional expense is recognized for any modification that increases the total fair value of the share-based payment arrangement at the modification date. Income Taxes The Company accounts for income taxes under the asset and liability method, whereby deferred tax assets and liabilities are determined based on the difference between the financial statement and tax bases of assets and liabilities using the enacted tax rates in effect for the year in which the differences are expected to affect taxable income. A valuation allowance is established when necessary to reduce deferred tax assets to the amounts expected to be realized. The Company recognizes uncertain tax positions when it meets a more-likely-than-not threshold. The Company recognizes potential accrued interest and penalties related to unrecognized tax benefits as income tax expense. Net Loss per Share of Common Stock The Company calculates basic and diluted net loss per common share attributable to shareholders i n conformity with the two-class method required for companies with participating securities. The Company considers all ea rly exercised stock options to be participating securities as the holders are entitled to receive dividends on a pari passu basis in the event that a dividend is paid on common stock. Under the two-class method, the net loss attributable to common stock is not allocated to the early exercised stock options as the holders do not have a contractual obligation to share in losses. Basic net loss per common share is calculated by dividing the net loss by the weighted-average number of common shares outstanding during the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss by the weighted-average number of common shares and potentially dilutive securities outstanding for the period. For purposes of the diluted net loss per share calculation, common stock options, restricted stock units and warrants are considered to be potentially dilutive securities. Because the Company has reported a net loss in all periods presented, common stock options and warrants are anti-dilutive and therefore diluted net loss per common share is the same as basic net loss per common share for those periods. Comprehensive Loss Comprehensive loss represents all changes in the stockholders’ equity except those resulting from distributions to stockholders. The Company’s unrealized foreign currency translation income (losses) and unrealized gains (losses) on marketable securities represent the two components of other comprehensive income that are excluded from the reported net loss for each of the reporting periods and has been presented in the consolidated statements of operations and comprehensive loss. Warrants The Company accounts for warrants for shares of common stock as equity in accordance with the accounting guidance for derivatives. The accounting guidance provides a scope exception from classifying and measuring as a financial liability a contract that would otherwise meet the definition of a derivative if the contract is both (i) indexed to the entity’s own stock and (ii) classified in the stockholders’ equity section of the consolidated balance sheet. The Company determined that the warrants for shares of common stock issued in connection with its prior debt arrangements are required to be classified in equity. Warrants classified as equity are recorded as additional paid-in capital on the consolidated balance sheet and no further adjustments to their valuation are made. Recently Adopted Accounting Standards In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2016-02, Leases (Topic 842), which requires that lessee's recognize a right-of-use asset and a lease liability for all leases with lease terms greater than twelve months in the balance sheet. In July 2018, the FASB issued ASU 2018-10 and ASU 2018-11, which provides clarification on the narrow aspects of the guidance and provide an additional transition method to adopt the new leases standard. In March 2019, the FASB issued ASU 2019-01, which provides clarification on implementation issues associated with adopting ASU 2016-02. The new leases standard must be adopted using a modified retrospective transition method and allows for the application of the new guidance at the beginning of the earliest comparative period presented or at the adoption date. In November 2019, the FASB issued ASU 2019-10, which revised the mandatory effective dates of the new leases standard. Further, due to the impact of the COVID-19, in June 2020, the FASB issued ASU 2020-05 to further defer the effective date for one year for entities in the “all other” categories. In the fourth quarter of 2021, the Company adopted Topic 842 for leases, using the modified retrospective method, applying Topic 842 to all leases existing at the date of initial application. The Company elected to use the effective date of January 1, 2021 as the date of initial application. Under the modified retrospective method, balances and disclosures prior to January 1, 2021 have not been restated. The Company elected certain practical expedients, which among other things, allowed the Company to carry forward prior conclusions about lease identification and classification. The adoption of ASC 842 had a material impact on the consolidated balance sheet as the standard requires the Company to measure and recognize a right of use asset and lease liability. The Company recognized $3.8 million of operating lease liabilities and approximately $3.5 million of operating lease right-of-use assets on the consolidated balance sheet as of January 1, 2021. The difference between the operating lease right-of-use assets and operating lease liabilities represented the existing deferred rent liability balance as of the adoption date of $0.3 million. The adoption of the standard did not have a material impact on the consolidated statement of operations and comprehensive loss and there was no impact to cash from or used in operating, financing or investing activities on the consolidated statement of cash flows. The adoption of ASC Topic 842 had no income tax impact to the financial statements. The Company accounted for the basis differences arising from ASC Topic 842 adoption in deferred taxes which was offset by a valuation allowance. In June 2016, the Financial Accounting Standards Board ("FASB") issued ASU No. 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”). FASB issued ASU 2019-05 in May 2019, ASU 2019-08 and ASU 2019-11 in November 2019 for codification improvements of Topic 326. In November 2019, the FASB issued ASU 2019-10, which defers the effective date of ASU 2016-13 for public companies that are eligible to be smaller reporting companies and all other companies, to fiscal years beginning after December 15, 2022, including interim periods within those fiscal years. In February 2020, the FASB issued ASU 2020-02, which provides guidance regarding methodologies, documentation, and internal controls related to expected credit losses. ASU 2016-13 revises the existing incurred loss impairment model with a forward-looking expected credit loss model which will result in earlier recognition of credit losses for certain financial instruments and financial assets. For trade receivables, the Company is required to estimate lifetime expected credit losses. For available-for-sale debt securities, the Company will recognize an allowance for credit losses rather than a reduction to the carrying value of the asset. ASU 2016-13 is effective for the Company’s fiscal year beginning January 1, 2021 on a modified retrospective basis. The Company adopted this standard effective for the year ended December 31, 2021, and the adoption did not have a material impact on the Company’s consolidated financial statements. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. ASU 2019-12 simplifies the accounting for income taxes by eliminating certain exceptions to the guidance in ASC 740 related to the approach for intraperiod tax allocation, the methodology for calculating incomes taxes in an interim period and the recognition of deferred tax liabilities for outside basis differences. ASU 2019-12 is effective in 2021 and interim periods within that year and permits for an early adoption. The Company adopted ASU 2019-12 effective January 1, 2021. The adoption of the guidance did not have a material impact on its financials statements and related disclosures. Recently Issued Accounting Standards Not Yet Adopted In May 2021, the FASB issued ASU 2021-04 “Earnings Per Share (Topic 260), Debt—Modifications and Extinguishments (Subtopic 470-50), Compensation— Stock Compensation (Topic 718), and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815- 40) Issuer’s Accounting for Certain Modifications or Exchanges of Freestanding Equity-Classified Written Call Options” ("ASU 2021-04") which clarifies and reduces diversity in an issuer’s accounting for modifications or exchanges of freestanding equity-classified written call options that remain equity classified after modification or exchange. An entity should measure the effect of a mo |