Intrinsic and extrinsic contributions to the passive moment at the metacarpophalangeal joint

The purpose of this investigation was to determine whether the passive rang e of motion at the finger joints is restricted more by intrinsic tissues (c ross a single joint) or by extrinsic tissues (cross multiple joints). The p assive moment at the metacarpophalangeal (MP) joint of the index finger was modeled as the sum of intrinsic and extrinsic components. The intrinsic co mponent was modeled only as a function of MP joint angle. The extrinsic com ponent was modeled as a function of MP joint angle and wrist angle. With th e wrist fixed in seven different positions the passive moment at the MP joi nt of eight subjects was recorded as the finger was rotated through its ran ge at a constant rate. The moment-angle data were fit by the model and the extrinsic and intrinsic components were calculated for a range of MP joint angles and wrist positions. With the MP joint near its extension limit, the median percent extrinsic contribution was 94% with the wrist extended 60 d egrees and 14% with the wrist flexed 60 degrees. These percentages were 40 and 88%, respectively, with the MP joint near its flexion limit. Our findin gs indicate that at most wrist angles the extrinsic tissues offer greater r estraint at the limits of MP joint extension and flexion than the intrinsic tissues. The intrinsic tissues predominate when the wrist is flexed or ext ended enough to slacken the extrinsic tissues. Additional characteristics o f intrinsic and extrinsic tissues can be deduced by examining the parameter values calculated by the model. Published by Elsevier Science Ltd.