CME Extensor Tendon Injuries: Acute Management and Secondary Reconstruction Kevin R. Hanz, M.D. Michel Saint-Cyr, M.D. Maynard J. Semmler, O.T.R. Rod J. Rohrich, M.D. Dallas, Texas Learning Objectives: After reviewing the article, the participant should be able to: (1) Describe the anatomy of the extensor tendons at the level of the forearm, wrist, hand, and fingers. (2) Recognize variations in the anatomy. (3) Master the hand examination and define the relevant findings in acute injuries of the extensor tendon(s). (4) Delineate the techniques for extensor repair in both acute and secondary (delayed) management. Summary: Extension of the fingers is an intricate process that reflects the combined action of two independent systems. The interossei and lumbricals constitute the intrinsic musculature of the hand. These muscles innervated by the median and ulnar nerves extend the proximal interphalangeal and distal interphalangeal joints and flex the metacarpophalangeal joints. The extrinsic extensors are a group of muscles innervated by the radial nerve, originating proximal to the forearm. The extrinsic digital extensor muscles include the extensor digitorum communis, extensor indicis proprius, and extensor digiti quinti. The digital extensors function primarily to extend the metacarpopha- langeal joints, but also extend the proximal interphalangeal and distal inter- phalangeal joints. Normal extensor physiology reflects a delicate balance be- tween these two unique extensor systems. In the injured hand, a functioning intrinsic system may potentially compensate for an extrinsic deficit. An under- standing of the relevant anatomy and an appreciation for the complex interplay involved in extensor physiology is necessary to recognize and manage these injuries. (Plast. Reconstr. Surg. 121: 109e, 2008.) ANATOMY Forarm There are two compartments of muscles, com- prising a superficial layer and a deep layer. The muscles of wrist extension, the extensor carpi ra- dialis brevis, extensor carpi radialis longus, and the extensor carpi ulnaris, originate on the lateral condylar ridge and lateral epicondyle of the distal humerus. These muscles along with the extensor digiti quinti make up the superficial layer. The deeper layer of muscles includes the fin- ger and thumb extensors. These muscles have a broad origin, including the lateral epicondyle, the proximal radius, the proximal ulna, and the in- terosseous membrane. 1,2 Wrist The tendons enter the hand through six com- partments formed by the extensor retinaculum. The first compartment contains the extensor pol- licis brevis and the abductor pollicis longus; the second, the extensor carpi radialis longus and ex- tensor carpi radialis brevis; the third, the extensor pollicis longus; the fourth, the four tendons of the extensor digitorum communis plus the extensor indicis proprius; the fifth, the extensor digiti quinti; and the sixth, the extensor carpi ulnaris (Fig. 1). The extensor indicis proprius and extensor dig- iti quinti typically lie deep and ulnar to the extensor digitorum communis at the metacar- pophalangeal joints. From the Department of Plastic Surgery, University of Texas Southwestern Medical Center, and the Parkland Health and Hospital System. Received for publication April 8, 2006; accepted November 1, 2006. Copyright ©2008 by the American Society of Plastic Surgeons DOI: 10.1097/01.prs.0000299469.16296.cb Disclosure: None of the authors has a financial interest in any of the products, devices, or drugs mentioned in the article. www.PRSJournal.com 109e