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.