The A4 pulley overlies the middle phalanx, providing the critical anchoring point for the FDP tendon as it generates DIP joint flexion. Its preservation is essential in flexor tendon reconstruction — sacrifice allows the FDP to bowstring across the middle phalanx, reducing DIP flexion efficiency. A4 is released only as a last resort in flexor tendon surgery.
Critical for DIP joint flexion by FDP; prevents FDP tendon bowstringing over the middle phalanx; the second most important pulley after A2.
A4 pulley preservation is mandatory in all FDP tendon surgeries — repair, reconstruction, and transfer. Zone 1 flexor tendon injuries (distal to A4) are relatively straightforward to repair because the A4 pulley protects the repair site from excessive force during rehabilitation. A4 rupture in rock climbers is less common than A2 but produces significant DIP flexion loss.
A4 pulley disruption producing FDP bowstringing over the middle phalanx and loss of efficient DIP flexion, managed by pulley reconstruction with a tendon graft looped around the middle phalanx in a figure-of-8 configuration.
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