1532 - Atypical Claw Hand Deformity Involving Digits 2–5 with Suspected Anomalous Innervation: A Case Report

Case Diagnosis: Atypical Claw Hand Deformity

Case Description: A 29-year-old right-handed male sustained a lifting injury to his right distal forearm at work four weeks prior to presentation. He subsequently developed clawing of digits 2–5, with hyperextension at the metacarpophalangeal joints and flexion at the interphalangeal joints—typically consistent with ulnar nerve palsy.
Initial electrodiagnostic studies performed four weeks post-injury showed moderate carpal tunnel syndrome with normal ulnar nerve findings. Due to the timing of the EMG post-injury, repeat testing was planned. In the interim, the patient underwent right carpal tunnel release and ulnar nerve decompression at the elbow. He initially improved, but symptoms recurred approximately one week postoperatively.
Repeat electromyography performed eight weeks after surgery revealed abnormal needle findings in the abductor pollicis brevis. Nerve conduction studies suggested median nerve injury at the wrist or distal forearm. High-resolution ultrasound and MRI showed a bifid median nerve proximal to the carpal tunnel; the ulnar nerve appeared structurally normal.

Discussions: Clinical, electrodiagnostic, and imaging findings suggest anomalous innervation between the median and ulnar nerves, with apparent median nerve injury and preserved ulnar nerve structure. These findings could be explained by the presence of ulnar branches to the lumbricals and interossei joining the median nerve, and a Martin-Gruber anastomosis is suspected. Alternatively, the median nerve may innervate all lumbricals and interossei. In such cases, median nerve injury may mimic ulnar neuropathy despite an intact ulnar nerve. It is compelling, however, that the patient experienced transient improvement following surgery—this may warrant further investigation.

Conclusions: Anomalous innervation should be considered when evaluating atypical hand deformities. Detailed EMG/NCS and high-resolution imaging are essential for accurate diagnosis and optimal management.