Confirmation of differential loading of lateral and central fibers of the extensor tendon.

A measurement technique was developed that enabled us to separate (and exclude) the effects of all viscoelastic moments from that produced by the extensor tendon itself. Knowing this moment at various joint positions allowed us to calculate the effective extensor moment arm at the proximal interphalangeal joint. Measurements made on lateral films enabled us to show which fibers of the extensor complex were tensed at various positions of the joint. The results obtained on three fresh cadaver long fingers confirmed the findings of Sarrafian-that in the flexed position, the most central fibers are tensed; whereas, in the extended position, the lateral fibers are tensed.