Strength of Tendon Repair Decreases in the Presence of an Intact A2 Pulley: Biomechanical Study in a Chicken Model

Abstract

Pulleys have an important role in digital flexion, but little is known about how the strength of a tendon repair is affected by a major pulley. We evaluated the difference in strengths of flexor tendon repairs in the pulley area when the pulley was intact or divided in a chicken tendon injury model. In each of 100 long toes of 50 Leghorn chickens, a complete, transverse laceration of the flexor digitorum profundus tendon was made in the region of the A2 pulley and was repaired surgically. The A2 pulley was preserved or was completely divided longitudinally. The toes were harvested by disarticulating through the knee joint, and placed at full extension, at 20 degrees , 40 degrees , or 60 degrees of distal interphalangeal (DIP) joint flexion, and at 40 degrees , 80 degrees , or 120 degrees of combined DIP and proximal interphangeal (PIP) joint flexion, and tendon repairs were loaded to failure in a materials testing machine. The force required for ultimate failure was statistically compared for each group. Ultimate tendon repair strength was significantly lower in toes with the A2 pulley intact than in those with the pulley vented when the toes were placed at full extension and at all tested degrees of DIP and PIP joint flexion, except at the most marked flexion. After A2 pulley division, tendon repair strength was 30% to 60% higher than flexed toes with the pulley intact. With an intact pulley, the tendon repair strength in the flexed toes was significantly lower than that in the fully extended toes, but after A2 pulley division, the strength was similar at all toe positions except at the most marked flexion. Chicken tendon repairs are substantially weaker when the A2 pulley is intact than when the pulley is completely divided. Loading of the tendon repair against an intact major pulley adversely affects repair strength. These findings suggest that tendon repair is less likely to fail when the A2 pulley is divided than when the pulley is intact; pulley venting may decrease the likelihood of repair ruptures.