Predicting thenar motor branch anatomy for a safer carpal tunnel release

This study introduces a new classification system for further defining anatomic variations of the TMB. When transverse carpal muscle is absent, the TMB is highly likely to arise from the radial aspect of the median nerve. In the presence of transverse carpal muscle, the origin of the TMB is unpredictable and is significantly more likely to arise from the median nerve more ulnarly than is typically seen. Under these circumstances, attempts should be made to identify the TMB prior to completing ligament division.