The effects of various load paths and different loads on the load transfer characteristics of the wrist.

An experimental model that incorporated a static positioning frame, pressure-sensitive film, and a microcomputer-based videodigitizing system was used to analyze the effects of different loading pathways and various loads on the contact area and pressures within the wrist joint. There was no statistically significant difference in loading the wrist with comparable weights through the second and third metacarpals, through all five metacarpals, or through weights suspended from the wrist flexor and extensor tendons. A nonlinear relation was discovered between increasing loads and greater overall contact areas. The general distribution of the contact between the scaphoid and the lunate contact areas was consistent at all of the loads tested with 60% of the total contact area involving the scaphoid contact area and 40% involving the lunate contact area. Loads greater than 46 pounds were not found to significantly increase the overall contact areas implying that the cartilage of the wrist joint was maximally compressed at loads of this magnitude. At loads higher than 46 pounds it appears that average high pressures increase in a more direct correlation with the increase in weight. The overall contact area even at the highest loads tested were not more than 40% of the available joint surface. The contact areas were not concentric or symmetric as is characteristic of the incongruance of the radio/triangularfibrocartilage (ulna)/carpal joint.