The silicone scaphoid: a biomechanical study.

Five fresh cadaver upper extremities were studied by use of a static positioning frame, pressure-sensitive film, and a microcomputer-based videodigitizing system, to assess the load-bearing characteristics of a scaphoid silicone implant within the radioulnarcarpal joint. Specimens were studied in their "normal" condition, after resection of the scaphoid, after placement of a scaphoid implant, and with a scaphoid implant and a simulated capitate-lunate-triquetrum-hamate fusion. The scaphoid silicone implant bore significant, although less, load than the normal scaphoid. Decreasing the size of the scaphoid implant decreased the load born by the implant. Decreased load through the scaphoid implant was compensated by the lunate. The addition of a limited carpal fusion did not significantly decrease the load born by a scaphoid implant. Therefore, the silicone scaphoid implant is a load-bearing implant even when undersized or placed in association with a limited carpal fusion.