A cadaver study of the effects of dorsal angulation and shortening of the metacarpal shaft on the extension and flexion force ratios of the index and little fingers.

Two experiments were performed on the second and fifth metacarpals of five normal cadaver hands. The forces obtained on full extension and flexion of the digits were measured. An oblique osteotomy was performed on the shaft of the metacarpal and fixed with dorsal angulation. The forces obtained on extension and flexion of the digits were measured. The relationships between the changes in force and the angle were analyzed. Flexion force decreased and extension force increased as the dorsal angulation increased, and these were significant beyond 30 degrees of dorsal angulation. The differences between index and little fingers were not significant. In the second experiment, the metacarpal bone was shortened at the osteotomy site, and the same measurements made. Flexion and extension forces both decreased, and were significant beyond 3 mm of shortening. The differences between index and little fingers were not significant.