Evaluation of Finger Tendon Transfer Surgery Using the Two-Dimensional Link Model Simulating Paralysis of Intrinsic Muscle

A finger component was modeled by four tendons of three extrinsic muscles and an intrinsic muscle attached on a two-dimensional three rigid links of finger skeleton. Moment arms of each tendon were assumed constant regardless of joint angles. Each muscle generates not only active force but also passive force as a function of changing of muscle length. By judging the capability of moment balance under given finger posture within the limits of each muscle force, the range of motion and the maximum fingertip force were estimated. These results of the paralytic finger were agreed well with the clinical experience. Postoperative effects for two common tendon transfers (Lasso procedure and Four-Tail procedure) were simulated. For Four-Tail procedure, one of the following muscles was selected as a motor, palmaris longs, extensor carpi radialis longus, extensor carpi radialis bervis, and flexor digitorum superficialis of ring finger. The functional defects caused by transferring these wrist muscles were evaluated with the decreasing of total maximum moments of the wrist joint. Calculated results suggested that Four-Tail procedure with extensor carpi radialis longus was superior to other procedures in restoration of both range of motion and fingertip force. It was also found that Lasso procedure corrects fingertip force well.