EXHIBIT 4(b) ------------ HANGER ORTHOPEDIC GROUP, INC., as Issuer, and THE ORIGINAL SUBSIDIARY GUARANTORS (as defined herein) and THE ADDITIONAL SUBSIDIARY GUARANTORS (as defined herein) and U.S. BANK TRUST NATIONAL ASSOCIATION, as Trustee ----------------- FIRST SUPPLEMENTAL INDENTURE Dated as of August 12, 1999 to INDENTURE Dated as of June 16, 1999 ----------------- 11 1/4% Senior Subordinated Notes due 2009 FIRST SUPPLEMENTAL INDENTURE, dated as of August 12, 1999, among Hanger Orthopedic Group, Inc., a Delaware corporation (the "Company"), each of the Company's Domestic Restricted Subsidiaries that was a party as a Guarantor to the Original Indenture referred to below (the "Original Subsidiary Guarantors"), each of the Company's Domestic Restricted Subsidiaries that is a party as a Guarantor to this First Supplemental Indenture (the "Additional Subsidiary Guarantors") (the Original Subsidiary Guarantors and the Additional Subsidiary Guarantors collectively referred to as the "Subsidiary Guarantors"), and U.S. Bank Trust National Association, a national banking association, as Trustee (the "Trustee"). WHEREAS, the Company, the Original Subsidiary Guarantors and the Trustee executed an Indenture, dated as of June 16, 1999 (the "Indenture"), in respect of up to $300,000,000 aggregate principal amount of the Company's 11 1/4% Senior Subordinated Notes due 2009 (the "Securities"); WHEREAS, Section 4.20 of the Indenture requires, under circumstances specified in Section 4.20, that the Company shall cause certain Subsidiaries of the Company to execute and deliver to the Trustee a supplemental indenture in form and substance satisfactory to the Trustee pursuant to which such Subsidiaries of the Company shall be named as additional Subsidiary Guarantors; and WHEREAS, all conditions and requirements necessary to make this First Supplemental Indenture a valid, binding and legal instrument in accordance with its terms have been performed and fulfilled and the execution and delivery hereof have been in all respects duly authorized. NOW, THEREFORE, in consideration of the above premises, each party agrees, for the benefit of the other and for the equal and ratable benefit of the Holders of the Securities, as follows: ARTICLE I AMENDMENTS Section 1. The Company, the Subsidiary Guarantors and the Trustee hereby amend the Indenture and agree that each of the Subsidiary Guarantors shall be a Guarantor for all purposes under the Indenture and the term "Guarantor" shall for all purposes under the Indenture specifically include both the Original Subsidiary Guarantors and the Additional Subsidiary Guarantors. ARTICLE II MISCELLANEOUS PROVISIONS Section 2.1. Terms defined. For all purposes of this First Supplemental Indenture, except as otherwise defined or unless the context otherwise requires, terms used in capitalized 1 form in this First Supplemental Indenture and defined in the Indenture have the meanings specified in the Indenture. Section 2.2. Indenture. Except as amended hereby, the Indenture and the Notes are in all respects ratified and confirmed and all their terms shall remain in full force and effect. Section 2.3. Governing Law. This First Supplemental Indenture shall be deemed to be a contract made under the laws of the State of New York, and for all purposes shall be governed by and construed in accordance with the laws of said state without regard to the principles of the conflict of laws provisions thereof. Section 2.4. Successors and Assigns. All agreements of the Company and the Subsidiary Guarantors shall bind their successors and assigns. Section 2.5. Multiple Counterparts. This First Supplemental Indenture may be executed in any number of counterparts, each of which shall be an original, but such counterparts shall together constitute but one and the same instrument. Section 2.6. Effectiveness. The provisions of this First Supplemental Indenture shall become effective immediately upon its execution and delivery by the Trustee in accordance with the provisions of Article Nine of the Indenture. Section 2.7. Trustee Disclaimer. The Trustee accepts the amendment of the Indenture effected by this First Supplemental Indenture and agrees to execute the trust created by the Indenture as hereby amended, but only upon the terms and conditions set forth in the Indenture, including the terms and provisions defining and limiting the liabilities and responsibilities of the Trustee, which terms and provisions shall in like manner define and limit its liabilities and responsibilities in the performance of the trust created by the Indenture as hereby amended, and, without limiting the generality of the foregoing, the Trustee shall not be responsible in any manner whatsoever for or with respect to any of the recitals or statements contained herein, all of which recitals or statements are made solely by the Company and the Subsidiary Guarantors by corporate action or limited liability company action or otherwise, the due execution hereof by the Company, and the Subsidiary Guarantors or the consequences (direct or indirect and whether deliberate or inadvertent) of any amendment herein provided for, and the Trustee makes no representation with respect to any such matters. 2 SIGNATURES IN WITNESS WHEREOF, the parties hereto have caused this Indenture to be duly executed, all as of the date first written above. COMPANY HANGER ORTHOPEDIC GROUP, INC. By: __________________________________________________________ Name: Ivan R. Sabel Title: Chairman and Chief Executive Officer By: __________________________________________________________ Name: Richard A. Stein Title: Secretary and Chief Financial Officer ORIGINAL SUBSIDIARY GUARANTORS: State or Other Jurisdiction of Incorporation or Name Organization ---- ------------ HANGER PROSTHETICS & ORTHOTICS, INC. Delaware SOUTHERN PROSTHETIC SUPPLY, INC. Georgia SEATTLE ORTHOPEDIC GROUP, INC. Delaware OPNET, INC. Nevada EUGENE TUEFEL & SON ORTHOTICS & PROSTHETICS, INC. Pennsylvania HPO ACQUISITION CORP. Delaware By: __________________________________________________________ Name: Ivan R. Sabel Title: Chairman, President and Chief Executive Officer 3 By: ___________________________________________________________ Name: Richard A. Stein Title: Secretary and Chief Financial Officer ADDITIONAL SUBSIDIARY GUARANTORS: State or Other Jurisdiction of Incorporation or Name Organization ---- ------------ NOVACARE ORTHOTICS & PROSTHETICS, INC. Delaware ADVANCED ORTHOPEDIC TECHNOLOGIES, INC. Nevada ADVANCED ORTHOPEDIC TECHNOLOGIES, INC. New York NOVACARE ORTHOTICS & PROSTHETICS HOLDINGS, INC. Delaware NOVACARE ORTHOTICS & PROSTHETICS WEST, INC. California NOVACARE ORTHOTICS & PROSTHETICS EAST, INC. Delaware ADVANCED ORTHOPEDIC TECHNOLOGIES (CLAYTON), INC. New Jersey ADVANCED ORTHOPEDIC TECHNOLOGIES (LETT), INC. West Virginia ADVANCED ORTHOPEDIC TECHNOLOGIES (NEW JERSEY), INC. New Jersey ADVANCED ORTHOPEDIC TECHNOLOGIES (NEW MEXICO), INC. New Mexico ADVANCED ORTHOPEDIC TECHNOLOGIES (NEW YORK), INC. New York ADVANCED ORTHOPEDIC TECHNOLOGIES (OTI), INC. New York ADVANCED ORTHOPEDIC TECHNOLOGIES (PARMECO), INC. West Virginia ADVANCED ORTHOPEDIC TECHNOLOGIES (SFV), INC. California ADVANCED ORTHOPEDIC TECHNOLOGIES (VIRGINIA), INC. Virginia ADVANCED ORTHOPEDIC TECHNOLOGIES (WEST VIRGINIA), INC. West Virginia 4 ADVANCED ORTHOPEDIC TECHNOLOGIES MANAGEMENT CORP. New York AD CRAIG COMPANY California ADVANCE ORTHOTICS, INC. Texas ADVANCED ORTHOPEDIC SYSTEMS, INC. California ADVANCED ORTHOTICS AND PROSTHETICS, INC. Washington ARTIFICIAL LIMB AND BRACE CENTER Arizona CENTRAL VALLEY PROSTHETICS & ORTHOTICS, INC. California CERTIFIED ORTHOPEDIC APPLIANCE CO., INC. Arizona FRESNO ORTHOPEDIC COMPANY California HIGH DESERT INSTITUTE OF PROSTHETICS AND ORTHOTICS California MCFARLEN & ASSOCIATES, INC. Texas PROFESSIONAL ORTHOTICS AND PROSTHETICS, INC. New Mexico PROFESSIONAL ORTHOTICS AND PROSTHETICS, INC. OF SANTA FE New Mexico PROGRESSIVE ORTHOPEDIC California ROBIN-AIDS PROSTHETICS, INC. California SALEM ORTHOPEDIC & PROSTHETIC, INC. Oregon SAN JOAQUIN ORTHOPEDIC, INC. California TEXOMA HEALTH CARE CENTER, INC. Texas TUCSON LIMB & BRACE, INC. Arizona AMERICAN REHABILITATION SYSTEMS, INC. Georgia ATLANTA PROSTHETICS, INC. Georgia BOWMAN-SHELTON ORTHOPEDIC SERVICE, INCORPORATED Oklahoma CAHILL ORTHOPEDIC LABORATORY, INC. New York DALE CLARK PROSTHETICS, INC. Iowa E.A. WARNICK-POMEROY CO., INC. Pennsylvania FRANK J. MALONE & SON, INC. Pennsylvania J.E. HANGER, INCORPORATED Missouri KROLL'S, INC. Minnesota MCKINNEY PROSTHETICS/ORTHOTICS, INC. Illinois MEADOWBROOK ORTHOPEDICS, INC. Michigan MEDICAL ARTS O&P SERVICES, INC. Wisconsin NORTHLAND REGIONAL ORTHOTIC 5 AND PROSTHETIC CENTER, INC. Minnesota OPUS CARE, INC. Illinois ORTHO EAST, INC. Massachusetts ORTHO-FAB LABORATORIES, INC. Illinois ORTHOPEDIC APPLIANCES, INC. Iowa ORTHOPEDIC REHABILITATIVE SERVICES, LTD. Illinois ORTHOTIC & PROSTHETIC REHABILITATION TECHNOLOGIES, INC. Florida ORTHOTIC SPECIALISTS, INC. Michigan ORTHOTIC AND PROSTHETIC ASSOCIATES, INC. Massachusetts PHYSICAL RESTORATION LABORATORIES, INC. Illinois PROSTHETICS-ORTHOTICS ASSOCIATES, INC. Illinois PROTECH ORTHOTIC AND PROSTHETIC CENTER, INC. Illinois REHABILITATION FABRICATION, INC. Massachusetts REID MEDICAL SYSTEM, INC. Florida SOUTHERN ILLINOIS PROSTHETIC & ORTHOTIC OF MISSOURI, LTD. Missouri SOUTHERN ILLINOIS PROSTHETIC & ORTHOTIC, LTD. Illinois T.D. REHAB SYSTEMS, INC. New Jersey UNIVERSITY ORTHOTIC & PROSTHETIC CONSULTANTS, LTD. Pennsylvania MICA CORPORATION Washington By: __________________________________________________________ Name: Ivan R. Sabel Title: President and Chief Executive Officer By: __________________________________________________________ Name: Richard A. Stein Title: Secretary and Director TRUSTEE; U.S. BANK TRUST NATIONAL ASSOCIATION, as Trustee 6 By: __________________________________________________________ Name: Richard Prokosch Title: Assistant Vice President 7