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American Association for Hand Surgery

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Effects of Complete A4 Pulley Release on Bowstringing of FDP Tendons in a Cadaveric Model
Michael C Holmboe, D.O.1, Shayne Kelly, DO1, Daniel Lara, MD1, Brenden Cutter, DO1, Eric Huish, D.O.1 and Marc Trzeciak, DO2, (1)Valley Orthopedic Surgery Residency, Modesto, CA, (2)Orthopedic Surgery, Valley Orthopedic Surgery Residency, Modesto, CA

Abstract:
Purpose: The A4 pulley aids in proper flexor tendon mechanics. Although its importance in preventing bowstringing has been well established, partial or complete release of the A4 pulley has gained attention in the setting of flexor tendon repair recently. If done properly, releasing these pulleys can improve functional recovery and is unlikely to cause clinical problems. The purpose of this study was to review the effect of complete A4 pulley release on FDP bowstringing in a cadaveric model and propose it as an alternative window to the accepted standard of C1, A3, C2 pulley releases.
Methods: The index, long, ring and small finger flexor digitorum profundus (FDP) tendons were studied on five cadaveric hands. The FDP tendon was exposed on each of the digits from the MCP to DIP joints through a midline volar incision. Manual traction was applied to the FDP tendon in order to form a composite fist. Measurements of pulp to palm distance and flexor tendon bowstringing were measured with intact pulley and with subsequent release of the A4 pulley, followed by the release of the C1, A3, and C2 pulleys as a unit. Bowstringing was measured using the distance from the middle phalanx to the dorsal aspect of the FDP tendon, using digital calipers.
Results: The measurement of bowstringing followed a normal distribution for the A4 released digits (p=0.097) and the C1-A4 released digits (p=0.071). ANOVA showed no difference in bowstringing between finger types with A4 released (p=0.119) or with C1-A4 released (p=0.467). The mean (± SD) bowstringing present as measured by the widest gap between the tendon and bone was 1.55 (± 1.00) mm in the A4 released group vs. 3.54 (± 1.30) mm in the C1-A4 released group. This difference was statistically significant (p=0.0002).
Conclusions: Our results support the evidence that the loss of the A4 pulley alone may be mechanically well-tolerated. However complete transection of A4-C1 results in significant anatomical bowstringing. Clinically, it is important for the surgeon to decide which window to work in. They can use either C1, A3, C2 window or A4 window but not both.


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