The Role of the A0 Pulley and the Flexor Tendons in Trigger Finger
Robin Wu, BS; Jack Kanouzi, MD; Cyril Gary, BA; Brandon Sumpio, BA; J. Grant Thomson, MD
Yale University School of Medicine, New Haven, CT
Background:The A0 pulley, just proximal to the A1, has been implicated a posteriori, by our group, in trigger finger, while no other studies have defined the role of the A0 in this pathology. The aims of this study were to (1) compare trigger finger with A1 or A0 pulley constriction and (2) to expound the role of differential grips, by way of differential FDS/FDP tension, in trigger finger.
Methods: A tensiometer (Instron High Precision Soft Tissue Testing System) was used to measure FDP work of flexion in four digits (index, middle, ring, and small) of two human cadaveric hand. The A1 and A0 pulleys were incrementally constricted in order to induce triggering. The FDS was either not tensioned or held at a constant tension of 5N (crimp grip) or 10N (slope grip) for every incremental constriction. Work of flexion was analyzed with the BlueHill2 software for differences among trial conditions. The tension normalized by circumference (TNC) was calculated as a standardized unit of pulley constriction on the tendon. The TNC at which the finger triggered (mTNC) was compared between conditions.
Results: Triggering was successfully induced with constriction of both the A1 and A0 pulley in the ring and small digits in hand 1 and the index and middle digit in hand 2. The mTNC was lower with constriction of the A0 in both the ring and small finger (ring 0.001, small 0.089) of hand 1 than the A1 (ring 0.063, small 0.106). The mTNC was lower with constriction of the A1 in both the index and middle finger (index 0.086, middle 0.076) of hand 2 than the A0 (index 0.204, middle 0.117). The magnitude of triggering increased significantly with increasing FDS tension in the small A0 and ring A0 and decreased significantly in the middle A1 and index A1. Increased tension applied to the FDS elicited triggering in the ring A0 and the small A0 and abolished triggering in the middle A1.
Conclusion: This is the first time the A0 pulley has been implicated in a cadaveric model of trigger finger. Thus, future surgical release of the A0 pulley may be necessary for comprehensive treatment of trigger finger in a subset of patients. Different grips, with distinct FDS/FDP involvement, alter the course of A0 and A1 trigger finger presentation in a predictable manner.
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