Movement of finger joints induced by synergistic wrist motion

Background. An experiment has recently been conducted to evaluate and compare the differences in tendon excursions between the flexor digitorum profundus and superficialis using three mobilization techniques. No previous studies deal with the total joint excursions with constant tendon length. The purpose of this study was to investigate the coordinated motion between the finger and wrist joints resulting from passive tension of the muscles while performing synergistic wrist motion. Methods. The relative joint positions of the hand and wrist were measured using a three-dimensional motion analysis system with external retroreflective markers 2 mm in diameter placed on the dorsal surface of the hand. Fifty normal subjects, with a 1:1 gender ration, ranging in age from 20 to 40 years, and with no previous history of upper extremity injury, were recruited for the experiment. Findings. The relationships of synergistic motion between the wrist and finger joints due to passive tension in the muscles were approximately linear. The ranges of wrist motion averaged 60° extension and 60° flexion. Moving the wrist from flexion into extension induced synergistic finger joint motion as follows: the distal interphalangeal joint angles changed from an average of 12° of flexion to 31°; proximal-interphalangeal joint angles changed from 19° to 70°; and metacarpal phalangeal joints changed from 27° to 63° of flexion. Interpretation. The relationships of synergistic motion between the wrist and finger joints were systematically documented. Such a relationship could be considered in optimizing the design of dynamic splints used for rehabilitation in post-surgical tendon repair, as well as providing useful information about potential diagnoses of problems with the integrity of the flexor and extensor mechanisms.