Tendon and pulleys at the metacarpophalangeal joint of a finger.

In fresh frozen traumatically amputated forearms with a constant tension of one kilogram on the flexor profundus tendon and the interphalangeal joints fixed in full extension by a Kirschner wire, the excursion of the tendon at the metacarpophalangeal joint and the force at the finger tip were correlated with different angles of flexion of the joint, first with the finger intact and then after varying amounts of advancement of the metacarpophalangeal joint pulley system. Pulley advancement increased the tendon excursion required to flex this joint and thus the mechanical advantage at this joint, but only when the joint was partly flexed. The extra excursion required at the metacarpophalangeal joint would be expected to weaken the interphalangeal joints at full flexion. Advancement also permitted ulnar-radial displacement of the tendon at the level of the metacarpophalangeal joint and hence could accentuate ulnar or radial drift. Pulley advancement is not recommended.