Carpal tunnel and transverse carpal ligament stiffness with changes in wrist posture and indenter size.

This study investigated the effects of loading and posture on mechanical properties of the transverse carpal ligament (TCL). Ten fresh-frozen cadaver arms were dissected to expose the TCL and positioned in the load frame of a servo-hydraulic testing machine, equipped with a load cell and custom made indenters. Four cylindrical indenters (5, 10, 20, and 35 mm) loaded the TCL in three wrist postures (30° extension, neutral and 30° flexion). Three loading cycles with a peak force of 50 N were applied at 5 N/s for each condition. The flexed wrist posture had significantly greater TCL stiffness (40.0 ± 3.3 N/mm) than the neutral (35.9 ± 3.5 N/mm, p = 0.045) and extended postures (34.9 ± 2.8 N/mm, p = 0.025). TCL stiffness using the 10 and 20 mm indenters was larger than the 5 mm indenter. Stiffness was greatest with the 20 mm indenter, which had the greatest indenter contact area on the TCL. The 35 mm indenter covered the carpal bones, compressed the carpal tunnel and produced the lowest stiffness. The complexity of the TCL makes it an important part of the carpal tunnel and the mechanical properties found are essential to understanding mechanisms of carpal tunnel syndrome.