Subperiosteal Ulnar Nerve Entrapment at the Wrist

Ulnar nerve entrapment at the wrist can cause debilitating sensory, motor, or sensory and motor deficits in the hand. The sources of compression have been well documented, with ganglions, lipomas, and trauma being common etiological factors. We treated a professional sculptor with intrinsic pain and weakness in her dominant hand because of compression caused by the subperiosteal course of her deep motor branch of the ulnar nerve. The nerve traversed on the radial side of the hook of the hamate and descended into the floor of the palm in the carpal tunnel through the transverse carpal ligament. We present this previously unreported anatomical anomaly and the subsequent operative treatment. Knowledge of this anatomical variation is paramount in avoiding injury to the ulnar nerve when operating the Guyon canal or carpal tunnel, among other hand and wrist surgeries.