Carpal hyperflexion in a growing dog following neural injury to the distal brachium

A three‐month‐old dobermann was presented with hyperflexion of the right carpus. The abnormality had evolved over a three‐week period, following circumferential soft tissue trauma to the distal brachium. The carpal joint angle measured at the limit of passive extension was 105° compared with 175° for the left carpus, and prevented placement of metacarpal and digital pads on the ground. Neurological examination revealed marked atrophy of the carpal extensors, an absent extensor carpi radialis reflex and moderate atrophy of the carpal flexors. Spontaneous electromyographic activity consistent with denervation was recorded in the carpal extensor and flexor muscles. Surgical exploration of the distal radial nerve disclosed a region of fibrosis enmeshing the deep branch of the radial nerve. Following relief of the entrapped nerve, carpal hyperflexion, muscle atrophy and the extensor carpi radialis reflex deficit gradually resolved over four months. It is suggested that, in the rapidly growing limb, myoneural dysfunction induced by trauma was the underlying pathophysiological mechanism for carpal hyperflexion.