Mechanical analysis of the palmar aponeurosis pulley in human cadavers.

The anatomy of the palmar aponeurosis pulley has been well described, but its biomechanical function is not as well characterized. This study describes the functional importance of the palmar aponeurosis pulley by using efficiency parameters. We obtained data by generating load, excursion, and work efficiencies in the intact pulley system and compared these to the efficiencies obtained after sectioning the palmar aponeurosis pulley alone and in combination with the proximal annular pulleys. The variability associated with comparisons between different fingers and hands was therefore diminished. Sectioning the palmar aponeurosis pulley alone did not significantly change any of the efficiency parameters. When the palmar aponeurosis pulley was sectioned in combination with either or both of the proximal annular pulleys (A1, A2) there was a significant decrease in excursion efficiency. Only after all three proximal pulleys were sectioned did the load efficiency increase and the work efficiency decrease significantly. These findings prove that the palmar aponeurosis pulley in combination with the proximal annular pulleys acts to decrease the tendency to bowstringing around the metacarpophalangeal joint. The increased load efficiency is probably the result of a decrease in friction and counteractive forces generated by the integrated fibers of the intact palmar aponeurosis pulley. Change in work is due not only to an increase in excursion, but also to the increased resistance that results from the acute angulation that the tendon must endure as it follows behind the remaining pulleys during flexion. Intergroup comparisons show a significant contribution by the palmar aponeurosis pulley. This study demonstrates a significant biomechanical role for the palmar aponeurosis pulleys and suggests that it be considered similar to the annular and cruciate flexor tendon pulleys in importance.