[Pisio-hamate hiatus syndrome].
Two patients with atrophy and weakness of intrinsic had muscles innervated by the deep branch of the ulnar nerve except abductor digiti quinti muscle and without any sensory symptoms were reported. They were house-wives aged thirty and fourty-four, respectively, without any specific history of trauma or occupation. Neurological and neurophysiological examination pointed out that the lesion situated in the deep branch of the ulnar nerve. Both of them were operated on. At operation, no abnormal structure were found in the canal of Guyon, though, the deep branch of the ulnar nerve was enlarged at the pisio-hamate hiatus where the branch to the abductor digiti quinti has taken off. In one of the cases, microsurgical removal of the epineurium of the deep branch revealed that each funiculus has lost its course into irregularly enlarged mass, which thought to be neoplastic change. In this case the deep branch was replaced by cable grafts about two centimeters in length by using the sural nerve. Histological findings of this case were as follows: there was no neoplastic or inflammatory change, there was no normal axon pa surviving and that very little regenerated axon and marked interneural fibrosis were observed, which indicates that the nerve lesion was caused by chronic compression. In the other case, the attachment of the membranous tendon of the flexor digiti quinti brevis and opponence digiti quinti muscle to the hook of the hamate was removed. No marked improvement was obtained in both of the cases, because they were too late to be operated on (ten and three years has passed since they noticed muscular atrophy, respectively).