Tendon Injury and Tendon Reconstruction
Zone anatomy governs outcome
Flexor zones. Verdan I (FPL/FDP insertion), II (the fibro-osseous tunnel, historically 'no man's land'), III (palm), IV (carpal tunnel), V (forearm). Zone II is unforgiving because the repair must glide beneath the A2 and A4 pulleys, the critical ones to preserve.
Repair. A strong core suture (4- or 6-strand) plus a running epitendinous suture reduces gapping and adhesion formation; protected early active motion begins within days. Injured pulleys are repaired or reconstructed with graft; unrepaired A2 loss causes bowstringing.
Two-stage reconstruction. When the bed is scarred or pulleys are lost, a silicone rod (Hunter) creates a pseudosheath, followed by grafting (palmaris longus, plantaris, toe extensors) in a second stage. Tenolysis is offered only after mature scar, usually 3–6 months, and only in a cooperative patient.
Extensor zones. Zone I mallet finger: tendinous injuries are splinted; bony injuries with a large fragment or volar subluxation are pinned or screwed. Zone III central slip injury produces a boutonnière deformity, and a neglected injury leaves a PIP flexion contracture from volar migration of the lateral bands. Zone VII attrition rupture of the EPL after a distal radius fracture is a classic finding - the patient cannot extend the thumb IP joint.
Traps: expecting a jersey finger (FDP avulsion, Leddy–Pack) to resolve; ignoring the quadriga effect; and confusing mallet finger with a swan neck deformity.
Rule of thumb: 4-strand core plus epitendinous stitch, and never repair a flexor tendon under tension in a contaminated wound.