Variations in the course of the thenar motor branch of the median nerve.

In a prospective study of 80 operations in 61 patients for carpal tunnel syndrome, special attention was given to the course of the thenar motor branch and its variations. An anomalous origin of the branch was found in 21%. Multiple motor branches occurred in 12.5%. Seventeen patients had operations on both hands, but anomalies were often found in one side only. Special attention is drawn to an additional anomaly where the motor branch lies superficially to the retinaculum buried in a hypertrophic preligamentous muscle. If this anomaly is not borne in mind, the nerve can easily be injured during splitting of the flexor retinaculum. We found this variation in 9% of our patients, but it is rarely mentioned in the literature and in many large series it is not described at all.