Passive properties of the forearm musculature with reference to hand and finger postures

OBJECTIVE: To quantify individual forearm muscle passive forces and evaluate their impact on hand function. DESIGN: The passive force-length properties of the 24 extrinsic hand and wrist muscles were determined in five fresh frozen cadaver arms. BACKGROUND: Muscle force production is a summation of the active and passive force components. The passive properties of the extrinsic finger musculature and wrist musculature appear to strongly affect both hand posture and hand movement. METHODS: The passive force-length properties of extrinsic hand and wrist muscles were determined by applying a slow, continuous extension to each muscle and recording the resulting tension. Each force-length curve was fit using exponential regression and were related to specific joint rotations and seven hand postures by calculating the muscle excursions for those postures. RESULTS: The exponential passive force-length relationship explained over 97% of the experimental variance. The largest passive forces were elicited in the digital extensors in grips involving large flexion angles such as tip pinch, key pinch, and a briefcase grip. CONCLUSIONS: The passive properties of the extrinsic finger musculature and wrist musculature affect both hand posture and movement especially in postures with flexed wrist and fingers.