This study was designed to investigate several biomechanical parameters involved in repair of extensor tendons in Zone IV (over the proximal phalanx). Typical suture techniques over the proximal phalanx did not shorten the tendon significantly nor was there significant loss of flexion at the metacarpophalangeal or proximal interphalangeal joints. The Kleinert modification of the Bunnell technique and modified Kessler technique seemed to be the strongest and provided evidence that dynamic or active range of motion, under controlled conditions and in short arcs, might be physiologically tolerated by repaired tendons.