Biomechanical evaluation of wrist motor tendons after fractures of the distal radius

We conducted a biomechanical study of changes in parameters of wrist motor tendons in fractures of the distal radius in 7 cadaveric extremities. Extra -articular distal radius fractures were simulated by distal radius osteotom y and fracture angulation was maintained by external fixators. Eight positi ons of the distal radius fractures were studied: dorsal angulation of 10 de grees, 20 degrees, 30 degrees, and 40 degrees and radial angulation of 5 de grees, 10 degrees, 15 degrees, and 20 degrees. Dorsal and radial angulation of the fractures were measured with respect to the shaft of the radius. Ex cursions of 5 principal wrist motor tendons extensor carpi radialis longus, extensor carpi radialis brevis, extensor carpi ulnaris, flexor carpi radia lis, and flexor carpi ulnaris were recorded simultaneously with wrist joint angulation using a computer-assisted recording system. Data were collected from intact wrists and from wrists with fractures at each of 8 positions o f angulation during wrist flexion and extension and radical and ulnar devia tion. Moment arm of the wrist motor tendons was derived from tendon excursi on and joint angulation. The results demonstrated that excursions and momen t arms of principal wrist motor tendons are significantly affected by dorsa l and radial angulation of distal radius fractures. Amplitude of changes in moment arms increased as the deformities became more severe. Statistical a nalysis revealed that dorsal angulation of 10 degrees or more significantly affected moment arms of all the prime wrist motors. Dorsal angulation of 3 0 degrees or 40 degrees changed the moment arms greatly. Radial angulation of 5 degrees did not affect moment arms of the tendons and angulation over 10 degrees had a statistically significant effect on the tendons. We conclu de that deformities of distal radius fractures have a significant influence on the biomechanics of the wrist motors. (J Hand Surg 1999;24A:121-132, Co pyright (C) 1999 by the American Society for Surgery of the Hand.)