Posterior Interosseus Palsy with an Incidental Froment-Rauber Nerve Presenting as a Pseudoclaw Hand

Abstract

IntroductionAnatomic variations of peripheral nerves are well recog-nized and reported in literature [4]. It is important tounderstand these variations because they can explainunusual clinical deficits or findings. The Froment–Raubernerve is a distal continuation of the motor branch of theposterior interosseous nerve, which innervates the firstdorsal interosseus muscle. This report discusses a case ofthis rare anomalous connection that initially confused thediagnosis of a posterior interosseus palsy.Case ReportA 17-year-old left-hand dominant baseball pitcher pre-sented with an 8-month history of progressive pain in hisleft proximal forearm and elbow. His symptoms proceededto subjective weakness of the small finger that progressedradially to include the ring and middle fingers withposturing in flexion at the metacarpal−phalangeal andinterphalangeal joints. He was given the presumptivediagnosis of an ulnar palsy. Prior to the onset of handweakness, there were previous episodes of elbow pain thatresolved without sequelae. He was referred to a handsurgeon. Initial physical examination was notable forclawing of the middle, ring, and small digits (Fig. 1) withfull passive mobility. Additionally, he had subtle weaknessof the wrist and extrinsic digit extensors as well as of theextensor pollicis longis and the abductor pollicis longus. Hedenied any sensory changes but slightly decreased protec-tive sensibility was noted in the ulnar nerve distribution bySemmes–Weinstein monofilament testing (3.61), includingthe dorsal ulnar cutaneous nerve. A mildly positive Tinel’ssign over the ulnar nerve at the elbow was detected.Nonoperative treatments of splinting and nonsteroidal anti-inflammatory agents had been attempted and had failed toimprove his symptoms.Electrodiagnostic studies (nerve conduction and electro-myography (EMG)) were consistent with a posteriorinterosseous nerve (PIN) neuropathy. These findings in-cluded denervation in the extensor carpi ulnaris and firstdorsal interosseus with complex repetitive discharges in thelatter. The number of motor units in all muscles innervatedby the posterior interosseus nerve as well as in the firstdorsal interosseus were decreased. Nerve conductionstudies of the median and ulnar nerves were normal,including the amplitude of the thenar and hypothenarcompound action potentials. The amplitude of the extensorindicis proprius compound muscle action potential wassignificantly decreased. Notable is that although no neuro-physiologic evidence of ulnar nerve pathology was found atthe elbow or wrist, evidence of denervation was noted inhis first dorsal interosseus muscle on EMG. A completeneurological evaluation including magnetic resonance im-aging of the brain, cervical spine, elbow, and forearm were