Effect of A3 pulley and adjacent sheath integrity on tendon excursion and bowstringing

The effect of the A3 pulley and adjacent sheath integrity on tendon functio n at the proximal interphalangeal (PIP) joint was investigated in 21 finger s in 7 fresh-frozen cadaver hands. Excursions of the flexor digitorum profu ndus (FDP) tendons were measured when the tendons were pulled to produce PI P joint flexion of 110 degrees from a resting position of 0 degrees. Excurs ions of the FDP tendons in 10 fingers were tested within the intact sheath and after incision of the A3 pulley, of the A3 pulley with its proximal she ath up to the distal border of the A2 pulley, and of the sheath between the A2 and A4 pulleys. Eleven fingers were tested after incision of the A3 pul ley, of the A3 pulley and its distal sheath up to the A4 pulley, and of the sheath from the A3 to A4 pulleys. Excursions of the FDP tendons increased to 103% +/- 3% after incision of the A3 pulley, 110% +/- 4% after incision of the A3 pulley and its proximal sheath, and 107% +/- 6% after incision of the A3 pulley and its distal sheath. Excursions increased to 116% +/- 6% a fter incision of the sheath from the A3 to A4 pulleys and to 119% +/- 3% af ter incision of the sheath between the A2 and A4 pulleys. Tendon bowstringi ng was 03 mm after incision of the A3 pulley, 0.6 mm after incision of the A3 pulley with its distal sheath, 0.8 mm after incision of the pulley with its proximal sheath, 1.4 mm after incision of the sheath from the A3 to A4 pulleys, and 1.6 mm after incision of the sheath between the A2 and A4 pull eys. The results suggest that the sheath adjacent to the A3 pulley plays an important role in restraining tendon bowstringing at the PIP joint, wherea s the A3 pulley alone is of little importance. This study elucidates the ro le of individual parts of the sheath around the PIP joint in maintaining te ndon function and may guide decisions regarding the area and length of the sheath feasible for surgical release or requiring repair in the treatment o f tendon lacerations. Copyright (C) 2001 by the American Society for Surger y of the Hand.