Carpometacarpal dislocation producing transient motor neurapraxia of the ulnar nerve

Carpometacarpal dislocation producing transient motor neurapraxia of the ulnar nerve

Q 1997 Injury Vol. 28, No. Elsevier Science 5-6, pp. 397-400, 1997 Ltd. All rights reserved Printed in Great Britain 0020-1383/97 $17.00 +O.O...

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Q 1997

Injury Vol. 28, No. Elsevier Science

5-6,

pp.

397-400,

1997

Ltd. All rights reserved Printed in Great Britain

0020-1383/97

$17.00

+O.OO

ELSEVIER

PII: SOO20-1383(96)00207-O

Carpometacarpal dislocation producing motor neurapraxia of the ulnar nerve A. L. Pimpalnerkar, Department

transient

R. Fakih and A. P. Thomas

of Orthopaedics,

New Cross Hospital,

Wolverhampton,

Injury, Vol. 28, No. 5-6,397-400,1997

Introduction Dislocation of the fourth and fifth carpometacarpal joints is an unusual injury, often associated with a significant degree of soft tissue injury’. The motor branch of the ulnar nerve is at risk of being injured in this region because of its close proximity. We report two cases of transient neurapraxia of the deep branch of the ulnar nerve following dorsal dislocation of the fourth and fifth carpometacarpal joints. Such injuries are likely to be missed in casualty because of the extensive soft tissue swelling, the apparent normal appearance of anteroposterior X-rays and the technical difficulty in testing the motor branch of the ulnar nerve in the presence of pain. We wish to emphasize the importance of being aware of such injuries and the necessity of prompt management.

Case reports Case 1

A 28-year-old forklift operator sustained an injury to his dominant right hand during a violent fist fight. He presentedwith a grossly swollen hand and clinical examination was difficult. Sensation in the hand and wrist was normal but there was distinct weaknessof the radial interossei and the adductor pollicis muscles. Radiographs showed dorsal dislocation of the fourth and fifth carpometacarpal joints (Figure la, b). Urgent closed reduction and percutaneousK-wire stabilization was done (Figure lc, d). The intrinsic muscleweaknessrecovered over the next 4 weeks. The K-wires were removed at 6 weeks and at 3 months follow-up the patient had regained excellent hand and wrist function. Case 2

A 26-year-old right-handed salesmanaccidentally struck a wall during a fight and presented with a swollen and bruised hand. There was a visible deformity on the dorsal

UK

aspectof the basesof the fourth and fifth metacarpals.The sensation to the hand was normal. There was distinct weaknessof the radial intrinsic and the adductor pollicis muscles. Radiographs showed dorsal dislocation of the fourth and fifth carpometacarpal joints (Figure 2a, b). Prompt closedreduction and K-wire stabilization was done (Figure &, d). The intrinsic weaknesspersistedfor the next 3 weeks. The K-wires were removed at 6 weeks and at 4 months follow-up the patient had regained full hand function.

Discussion Dislocation of the fourth and fifth carpometacarpal joints is likely to damage the motor branch of the ulnar nerve because of its close proximity to the unyielding ligaments and bone in this area. According to Kaplanz, the motor branch of the ulnar nerve begins at the level of the pisiform. As it passes around the hook of the hamate, it innervates the interossei, the two medial lumbricals and the adductor pollicis muscle. The carpometacarpal joints have strong volar and dorsal ligaments and a significant degree of injury is required to disrupt them, often leading to surrounding soft tissue injury as well. Shea and McClain3 reported 19 causes of compression lesions of the ulnar nerve in the wrist and hand and none of these was attributable to carpometacarpal dislocations. Gore4 reported a case of ulnar nerve injury following volar dislocation of the fourth and medial dislocation of the fifth carpometacarpal joints. Our report includes two cases of ulnar nerve injury following dorsal dislocation of the fourth and fifth carpometacarpal joints. These injuries can easily be missed in Casualty departments because of the extensive soft-tissue swelling and the difficulty in testing the motor function of the ulnar nerve in the presence of pain. EMG study at the time of injury is of limited value6 as it shows normal muscle innervation. It is important to obtain proper radiographs and interpret them in the Casualty departmentP. Fisher et al.’ draw attention to the loss of parallelism of the

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Figu Ire 1. Case 1. u, b, Anteroposterior

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Figu re 2. Case 2. a, b, Anteroposterior and lateral radiographs;c, d, postoperative radiographs.

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carpometacarpal joint surfaces (the so-called ‘M’ line). This parallelism is not always obvious due to errors

in projection and it is therefore important to obtain true lateral radiographs. In order not to miss ulnar nerve injury in dislocations of the fourth and fifth carpometacarpal joints we wish to emphasize the importance of testing the radial intrinsics as well as the adductor pollicis muscle.

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References Fisher MR, Rogers LF and Hendrix RW. Systematic approach to identifying fourth and fifth carpometacarpal joint dislocations.Am J Radio1 1983;140:319. Kaplan EB. Functional and Surgical Anatomy of the Hand. Philadelphia:JB Lippincott, 1965,p. 160. Shea JD and McClain EJ. Ulnar nerve compression syndromes at and below the wrist. 1 Bone Joint Surg [AmI 1969; 51A: 1095.

Conclusion We wish to draw attention to the association of neurapraxia of the deep branch of the ulnar nerve with dorsal dislocation of the ulnar carpometacarpal joints. Early diagnosis and prompt treatment favours a good prognosis.

Acknowledgements We wish to thank Mr M. A. M. Arafa for his guidance and Mrs Susan Hague for her help in preparing this manuscript.

Gore DR. Carpometacarpaldislocation producing compression of the deep branch of the ulnar nerve. J Bone Joint Surg [Am] 1971;53A: 1387. HendersonJJ and Arafa MAM. Carpometacarpaldislocation. An easily misseddiagnosis.I Bone Joint Surg [Brl 1987;69B: 212. Pierce DS. Electrodiagnosisin orthopaedic surgery. C/in Orfhop 1975; 107: 25.

Paper accepted 9 December 1996. Requests for reprints should be addressed fo: Dr A. L. Pimpal-

nerkar, MS(ORTH), 898 7UB, UK.

DNB(ORTH),

Alexandra Hospital, Redditch