Ulnar nerve compression by an anomalous muscle following carpal tunnel release: a case report.

We describe the acute development of ulnar nerve compression following carpal tunnel release in a patient with an accessory palmaris longus muscle. Although anomalous muscles in the wrist are relatively common and may produce ulnar nerve compression, this particular occurrence following carpal tunnel release has not been previously described in the literature. We theorize that the compression of the ulnar nerve proximal to Guyon's canal was caused by increased tension along the long axis of the anomalous accessory palmaris longus muscle as a consequence of transverse carpal ligament division.