Anatomical variations of the median nerve in the carpal tunnel.

The median nerve was explored in 100 hands and the variations classified by the Lanz system. Only 47.7% of hands showed the standard anatomy described in textbooks. Rare variations were also found. Knowledge of the variable anatomy of the nerve could help to avoid incomplete decompression at operations for carpal tunnel entrapment and injury to the thenar branch of the nerve. The possibility of double thenar innervation must be considered in preoperative evaluation and in the follow up of median nerve injuries.