Ulnar tunnel syndrome caused by anomalous muscles. Case report

Two cases of ulnar tunnel syndrome at the wrist are described. In both cases an anomalous hypothenar muscle, flexor digiti minimi brevis accessorius, was in part the causative factor. Contributing to the symptoms of nerve compression was swelling associated with rheumatoid disease and Colles' fracture, respectively. Decompression of the nerve including subtotal removal of the anomalous muscle effected complete recovery. Its phylogeny, morphology and clinical significance are discussed in relation to previously described anomalies of the hypothenar muscles.