Coexistence of multiple anomalies in the carpal tunnel.

We determined the frequency of anomalous structures within the carpal tunnels of 89 cadaveric forearm-hand specimens. We also examined these same specimens for variations in the branching pattern of the median nerve, and analyzed the range in length and width of the lumbricals. Many of the hands contained extra tendinous slips from the long flexors within the tunnel, subligamentous thenar branches of the median nerve, or lumbricals with bipennate origins. Only one hand had an anomalous muscle belly within the tunnel, two had persistent median arteries, two had high division of the median nerve in the distal forearm, and eight had lumbricals with lengths or widths that were greater or less than 2 standard deviations (SD) from the mean. Twenty-nine percent of all hands examined had two to five anomalies/variations per tunnel, whereas another 27% had one anomaly or variation per tunnel. More right hands (17%) than left (11%) contained two to five anomalous/variant structures per carpal tunnel. More right hands (19%) than left (8%) contained only one variant/anomalous structure per carpal tunnel. Anticipation of the frequency and multiplicity of anomalous structures and variations within this region is of importance to clinicians, particularly surgeons.