[Lesion of the deep branch of the ulnar nerve caused by fracture of the hook of the hamate].

We present a case of lesion of the deep branch of ulnar nerve at the wrist caused by fracture of the hook of the hamate. According to Wu's classification (1985) based on clinical and electromyographic findings and the clinicoanatomic correlations, our case corresponds to type IV of this classification with a pure motor ulnar neuropathy with sparing of hypothenar muscles. Improvement was observed after surgery.