Reconstruction of the A4 Pulley with a Lateral SLIP of Flexor Digitorum Superficialis

Injuries at the A4 pulley have a significant negative effect in flexor tendon mechanism function¹. We aimed to develop an animal model to perform biomechanical tests and compare the biomechanics of A4 flexor tendon² pulley reconstruction with an oblique vector technique (OVT) described by the authors with a currently used transverse vector technique (TVT)³.

Materials and Methods: The effect of A4 pulley transection in DIP joint flexion strength and angles was determined in 10 chicken feet⁴. Thirty-two long toe’s A4 flexor pulleys were transected and reconstructed with either OVT, using one slip of the flexor digitorum superficialis (n: 16), or TVT using tendon loops (n: 16). We measured DIP joint flexion degree and strength with the intact, transected and reconstructed pulleys using a device specifically designed for this study.

Results: Intact pulley feet were found to achieve a mean flexion of 96.5° at the DIP joint, with an increase in the angle (decrease in flexion) of 19.8% after A4 pulley section (96.5° to 115.6°; p< 0.001). DIP flexion strength decreased by 15.2% after A4 flexor pulley transection (from 8.16 psi to 6.92 psi; p < 0.001). In the 32 intervened chicken feet, differences in flexion angle of 1.23° (p= 0.03) and flexion strength of 0,026 psi (p= 0.6) in favor of OVT were found. Conclusions: Given the critical role the A4 pulley plays in their flexor function, chicken feet are an appropriate model to evaluate such pulley. The oblique vector reconstruction technique described provides biomechanical properties that are equivalent to those obtained with loop technique with a transverse vector

Conclusions: The A4 pulleys in chickens, like in humans, plays a fundamental role in the adequate functioning of flexor system specifically for the DIP flexion, making this animal model appropriate to perform biomechanical studies. The biomechanical behavior of the reconstructed A4 pulley with the OVT is equivalent to the TVT 

References

1. Arora R, Fritz D, Zimmermann R, Lutz M, Kamelger F, Klauser A, Gabl M. Reconstruction of the digital flexor pulley system: a retrospective comparison of two methods of treatment. The Journal of Hand Surgery. February 2007;32e(1)
2. Amirouchea F, Gonzalez M, Koldoffb J, Tiococ J, Hamc K. A biomechanical study of the finger pulley system during repair. Technology and Health Care 10 2002; pp. 23-31
3. Bunnell S, Böhler J. Die chirurgie der hand. Wein, Wilhlem Maudrich Verlag, 1958; 1:533-643
4. Farkas LG, Thomson HG, Martin R. Some practical notes on the  anatomy of the chicken toe for surgeon investigators. Plast Reconstr Surg 1974;54:452-458