LUMBRICAL MUSCLE INCURSION INTO THE CARPAL-TUNNEL DURING FINGER FLEXION

Carpal tunnel syndrome is one of the many so-called cumulative trauma disorders thought by some to be related to the performance of repetiti ve tasks in the work-place. The cause of this disorder is unknown. We have observed lumbrical muscle incursion into the carpal tunnel during finger flexion. This study was conducted to determine the amount of t his incursion in normal wrists. Five cadaver upper limbs were analyzed radiographically with radiopaque markers on the flexor retinaculum an d the lumbrical muscle origins in four finger positions: full extensio n, 50% flexion, 75% flexion, and 100% finger flexion. The lumbrical mu scle origins were an average of 7.8 mm distal to the carpal tunnel in full finger extension. They moved an average of 14 mm into the carpal tunnel with 50% finger flexion, 25.5 mm with 75% flexion, and 30 mm wi th 100% flexion. Abnormal lumbrical muscles have been cited as a possi ble cause of carpal tunnel syndrome. These findings suggest that lumbr ical muscle incursion during finger flexion is a normal occurrence and is a possible cause of work-related carpal tunnel syndrome.