Traumatic dislocation of the long-finger extensor tendon. A clinical, anatomical, and biomechanical study.

Five cases of traumatic dislocation of the extensor tendon of the long finger are presented. The anatomical defect consists of loss of continuity between the radial intrinsic muscles and the extensor tendon. The extensor tendon of the long finger sits on top of the proximal portion of the transverse fibers where it is maintained by a relatively poor fibrous attachment. The force tending to displace the normally situated extensor ulnarward is greatest in full extension, decreases during the first 60 degrees of flexion, and subsequently increases as flexion increases from 60 to 90 degrees. The force required to prevent further ulnar dislocation is large once the tendon is displaced. Simple primary repair is usually satisfactory for traumatic dislocation of the extensor tendon.