A biomechanical study of the flexor digitorum superficialis: effects of digital pulley excision and loss of the flexor digitorum profundus.

Many reports have been devoted to characterizing the significance of the pulleys for the flexor digitorum profundus (FDP). However, no comparable work has been published on the flexor digitorum superficialis (FDS). This study characterized the FDS in a human cadaver model. Eleven fresh-frozen cadaver hands were used. By using a tensiometer, data were gathered for tendon excursion, tendon load, and work of flexion. Changes in efficiency were caused by excision of annular pulleys A1, A2, A3, and the palmar aponeurotic pulley. We also measured the effect of FDP excision on FDS efficiency. Sectioning of the A2 and A3 pulleys together caused statistically significant losses of efficiency in all three parameters (work, load, and excursion). When the FDP was removed from a finger with an intact pulley system, losses in both work and excursion efficiencies were significant. Removing the FDP while cutting different pulleys caused significant decrease in FDS excursion efficiency. We conclude that A2 and A3 are the most important pulleys for maintaining normal FDS function, and that the presence of the FDP in the digital sheath is essential for optimal FDS excursion efficiency.