Electrophysiologic basis of dynamic extensor splinting

The use of dynamic extension splinting in the rehabilitation of extensor tendon injuries is gaining interest because of its apparent ability to improve clinical results. With such splinting, the extensor musculature is theoretically quiescent during both active flexion and rubber band-mediated extension; the gliding produced thereby decreases adhesion formation. Our initial intent was to perform electromyographic studies on volunteers in dynamic extension splinting to test this electrophysiologic principle. It was found, however, that only 16% of normal volunteers have quiescent extensor digitorum communis muscle activity within the dynamic extension splint typically used in this type of rehabilitation. A second splint was developed with a dorsal hood to keep the metacarpophalangeal joints in approximately 15 degrees of flexion. In this splint, 18 of 19 volunteers (95%) showed no extensor activity. The explanation for this phenomenon is not yet clear, but it shows that splint design plays a more significant role than previously expected. The expected electrophysiologic principle of dynamic extension splinting for extensor tendon injuries has been validated, but only in a splint design that is not commonly used.