The flexor tendons of each finger (FDS and FDP) run through a fibro-osseous tunnel from the carpal tunnel to the distal phalanx, guided by five annular (A1-A5) and three cruciate pulleys that maintain the tendons close to the phalanges to maximise mechanical efficiency. The A2 pulley (over the proximal phalanx) and A4 pulley (over the middle phalanx) are the most critical biomechanically and must be preserved during flexor tendon surgery. Zone II in the digital sheath is the most challenging zone for repair because both FDS and FDP must be managed in the confined sheath.
Finger flexion through the A1-A5 pulley system of each finger; grip force transmission
Zone II flexor tendon repairs require meticulous multi-strand core suture technique and immediate controlled active mobilisation protocols to prevent adhesion formation in the tendon sheath. The Strickland criteria assess outcomes by measuring the total active motion of the PIP and DIP joints post-repair. Trigger finger (stenosing tenosynovitis at the A1 pulley) produces a clicking or locking finger from the FDS and FDP tendons catching on the thickened A1 pulley annulus — managed with A1 pulley corticosteroid injection or surgical release.
FDS and FDP division in the digital sheath requiring primary repair with controlled active mobilisation to prevent adhesions in the critical no man's land zone.
A1 pulley stenosing tenosynovitis producing finger clicking and locking managed with corticosteroid injection or surgical pulley release.
