Analysis of Intrinsic-Extrinsic Muscle Function Through Interactive 3-Dimensional Kinematic Simulation and Cadaver Studies

Intrinsic muscle contribution to flexion moment at the index MCP joint is not as high or as low as previously reported. The relative moment production is governed by both the moment arms and tension produced by the muscle; thus a more precise knowledge of moment arms is essential to understand muscle balance at a joint. Clinically the hand surgeon should expect a loss of 24% of index MCP flexion moment-generating capacity in the intrinsic-minus index finger and a loss of 22% in the index finger on a hand with low ulnar nerve palsy. Furthermore the flexion moment from the lumbrical of only 2% appears to be adequate to prevent clinical clawing of the digit.