Biomechanics of pulley reconstruction.

The biomechanics of the reconstructed flexor retinacular pulley system are poorly defined. We used a mathematical theoretical model, confirmed by a cadaver model, and a clinical radiographic model to evaluate a variety of different joint and pulley combinations. We examined twenty-four sets of radiographs of 12 fingers in 9 patients for whom excursion was measured and predicted by the mathematical model. The 30 pulley combinations evaluated in the in vitro cadaver model showed statistical correlation with the biomechanical mathematical model. Recommendations of clinical application on the basis of this information include the following: (1) Two pulleys should be placed, one proximal and one distal to each joint. (2) These two pulleys should be balanced about the joint axis both in distance from the axis and in pulley height. (3) They should be positioned at the edge of the flare of the metaphysis. (4) The three individual joints can be balanced, one to another, by maintaining minimal bowstringing at all three joints. In this way, the relative excursion at the joint and torque at the joint will be maintained in a physiological ratio as close to normal as possible.