Isolated Injury of the Posterior Interosseous Nerve Complicating a Deep Laceration of the Proximal Forearm Dorsolateral Muscles: A Case Report

Abstract

Isolated injuries of the posterior interosseous nerve (PIN) or its branches without additional damage of the superficial radial nerve are rare and are usually caused by penetrating injuries.1–3 Injuries of the PIN caused by extensive proximal forearm lacerations without damage of the superficial sensory branch of the radial nerve have not been yet reported to the best of our knowledge. Although 12 cases of PIN palsies caused by forearm lacerations are mentioned in several articles in the English literature,4–6 in none of them the above combination is described. In such a case, the intact sensation could mask the underlying motor neuronal damage, because the loss of both carpal and finger extension can be satisfactorily explained by the extensor muscles laceration. The radial nerve divides into the PIN and the superficial radial nerve within an area 3 cm proximal or distal to the elbow joint. The PIN enters the radial tunnel and rests directly superficial and anterior to the radiocapitellar joint, before entering the supinator muscle through the Arcade of Frohse.7 As the PIN exits the supinator, it divides into two major branches: the recurrent branch, supplying the superficial layer of extensor muscles (extensor digitorum communis, extensor digiti minimi, and extensor carpi ulnaris), and the descending branch for the deep extensors (abductor pollicis longus, extensor pollicis longus and brevis, and extensor indicis proprius).8 We report a case of wrist and all five fingers drop caused by an extensive forearm laceration at the level of the radial neck without any sensory loss of the hand. The main feature of the injury was the PIN damage before its division to its major branches, which was diagnosed by careful clinical examination on musculoskeletal and neurologic basis and treated immediately postinjury. CASE REPORT A 55-year-old man who was carrying a 2 m 2.5 m large, 4-mm thick glass plate, sustained an injury, while loading the plate on a truck and holding it above his head. The plate was cracked and a large fragment fell on the dorsolateral side of his right forearm, just below the elbow joint, causing an extensive laceration wound of 10 cm in length (Fig. 1). At admission, the patient was unable to extend the wrist and all five fingers, while sensation over the whole area of the radial nerve distribution was unaffected. The clinical manifestation was primarily attributed to the muscle injury, and the patient was referred to the orthopaedic team for further treatment. Although the loss of carpal and finger extension could be explained by the extensor muscles laceration, it was the observed lack of thumb extension, which raised the suspicion of a possible neuronal involvement, because both extensor pollicis longus and extensor pollicis brevis muscles originate at the middle third of the dorsal side of the forearm, hence more distally to the injury site.9 The surgical exploration was performed by one (P.K.G.) of our two qualified upper limb surgeons trained in microvascular surgery. One of them is always available and in charge of dealing with such complicated neurovascular upper limb injuries. Intraoperatively, the wound was extended proximally and distally, and the extensor muscles of the posterior compartment (extensor digitorum, supinator, extensor digiti minimi, and extensor carpi ulnaris) as well as the muscles of the mobile wad (brachioradialis, extensor carpi radialis longus, and extensor carpi radialis brevis), were found to be totally severed through the muscle belly. The PIN was also identified to be completely crosscut, in contrast to the intact superficial, sensory branch of the radial nerve (Fig. 2, A). After a thorough surgical preparation, the proximal and distal nerve endings were mobilized. The nerve injury was a “clear-cut” injury without significant neuronal tissue loss, and the nerve endings could be reapproximated without tension. Furthermore, the fascicular orientation could be easily identified. Taken these facts into consideration, epineurial suturing was chosen and was performed under 3.5 magnification without tension, using microsurgery instruments with 8-0 blue, monofilament, nonabsorbable polypropylene sutures (Medipac, Kilkis, Greece). The epineurial suturing consisted Submitted for publication May 10, 2007. Accepted for publication July 20, 2007. Copyright © 2009 by Lippincott Williams & Wilkins From the First Orthopaedic Department, Aristotle University, G. Papanikolaou General Hospital, Thessaloniki, Greece. Address for reprints: Dr. Panagiotis Givissis, MD, PhD, 9 Papanikolaou Street, Panorama, Mail Box 215, 55210 Thessaloniki, Greece; email: givissis@otenet.gr.