Orthopaedic Sports Medicine

Answer 1 (D) Extension of the thumb. The combination of proximal or middle ulnar fracture and concomitant radial head dislocation is known as the Monteggia fracture-dislocation. The deep branch of the radial nerve (the posterior interosseous nerve [PIN]) is often injured due to its intimate association with the radial head and neck. The PIN provides innervation to the muscles of the posterior compartment of the arm, including the extensor pollicis longus, extensor pollicis brevis, and extensor digitorum. Therefore, a PIN lesion manifests as weakness or paralysis in thumb and finger extension.1 Forearm extension is controlled by the radial nerve proximal to the elbow and therefore provides innervation to the forearm extensors and would not be affected by a radial head dislocation. Flexion of the wrist and fingers is controlled by the median and ulnar nerves, abduction and adduction of the fingers are controlled by the ulnar nerve, and the median nerve controls thumb opposition.2 REFERENCES 1. Perron AD, Hersh RE, Brady WJ, Keats TE. Orthopedic pitfalls in the ED: Galezzi and Monteggia fracture-dislocation. Am J Emerg Med 2001;19:225-8. 2. Ruddy S, Harris ED, Sledge CB, editors. Kelley’s textbook of rheumatology. 6th ed. Philadelphia: WB Saunders; 2001. Click here to return to the questions

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