Flexor Tendon Injuries
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Direct answer
Zone II of the flexor system — from the A1 pulley to the insertion of flexor digitorum superficialis — was long called "no man's land" because both tendons run together in a tight fibro-osseous tunnel where repairs adhesed; modern multi-strand repairs have made primary repair standard even here, but the label still predicts difficulty. Verdan's five zones (I distal to FDS insertion; II A1 pulley to FDS insertion; III the palm; IV inside the carpal tunnel; V distal forearm) apply to every laceration, and the examination tests each tendon alone: profundus by blocking the proximal joints and flexing the distal interphalangeal joint, superficialis by holding the other fingers extended and flexing the proximal interphalangeal joint. Jersey finger, an FDP avulsion from the distal phalanx of the forcefully extended ring finger, is graded by Leddy-Packer and needs urgent repair. Postoperative protected early motion prevents the adhesions that defeat the surgery.
What you must remember
- Zones by function: I — FDP alone (DIP flexion lost); II — FDS and FDP, the historic no man's land; III — palm; IV — carpal tunnel with the median nerve; V — distal forearm; the thumb follows its own trizonal FPL system.
- Examination logic: FDP tested with MCP and PIP blocked (flex DIP), FDS with adjacent fingers held extended (flex PIP); a finger extended in the resting cascade with a palmar wound is severed until proven intact.
- Jersey finger (Leddy-Packer): type I retracts to the palm, blood supply disrupted, repair within 7-10 days; type II retracts only to PIP; type III avulses a large bony fragment caught at the A4 pulley; the ring finger is classic.
- Repair principles: primary repair within 24 hours or delayed primary within about 2 weeks; modified Kessler core suture plus epitendinous stitch aiming for 4-6 strands; partial cuts under 60 per cent may be trimmed.
- Pulley respect: preserve A2 and A4 — their loss causes bowstringing and needs reconstruction.
- Rehabilitation protocols: Kleinert rubber-band active extension with passive flexion; Duran controlled passive motion; modern early active short-arc protocols with a dorsal blocking splint.
- Complications: adhesions (tenolysis at 3-6 months), rupture in 2-5 per cent, and quadrigia.
A worked case from injury to tenolysis
A 28-year-old machine operator slices his right small finger and palm on a metal sheet. The small finger lies extended while the others rest in normal cascade. Blocking the metacarpophalangeal and proximal joints, he cannot flex the DIP (FDP gone), and with the other fingers extended the PIP will not flex (FDS gone): a zone II injury of both tendons near the A2 pulley. Exploration under tourniquet extends the wound in Bruner zig-zag fashion and repairs both tendons with a four-strand core suture and epitendinous stitch, preserving the pulleys. The hand is splinted in the dorsal blocking position and a Duran-style passive protocol starts on day two.
At five weeks the splint comes off; at three months passive flexion is full but active flexion 60 degrees short — adhesions, the expected adversary of zone II. Tenolysis follows once the repair is strong and joints supple. The case teaches the standing principle: surgery buys a gliding surface for six weeks and rehabilitation protects it. In Indian hand-injury practice, glass and machine lacerations dominate while certified hand therapists concentrate in metros, so a printed protocol and telephonic therapy schedule matter more than in fully serviced systems.
Where students slip
The first slip is skipping tendon examination because the wound looks trivial — a 1 cm palmar cut can divide both tendons and the digital nerve, so cascade, individual testing and two-point discrimination precede closure. The second is accepting combined-finger flexion as proof of integrity; each tendon is tested with the other blocked, and the DIP test is the one that fails in zone I. The third is the jersey finger misdiagnosis — the radiograph shows a fleck or nothing, the DIP cannot flex, and the injury is called a sprain until the tendon retracts and the week-long repair window closes. Examiners like "why the ring finger" (it grips the jersey first) and quadrigia.
Frequently asked questions
Why is flexor tendon zone II called no man's land?
FDS and FDP travel together in a tight fibro-osseous sheath where repairs historically adhesed badly; multi-strand repair with early mobilisation has improved results, but it remains the most demanding zone.
How are FDP and FDS tested separately?
FDP by blocking the MCP and PIP joints and flexing the DIP; FDS by holding adjacent fingers extended and flexing the tested PIP.
What is a Leddy type I jersey finger?
Avulsion of FDP from the distal phalanx with retraction into the palm and loss of vincular supply, requiring urgent repair within 7-10 days.
Which pulleys must be preserved and why?
The A2 and A4 annular pulleys — their loss causes bowstringing across the joints, costing excursion and therefore flexion.
When is tenolysis considered after repair?
When passive far exceeds active flexion at 3-6 months with a healed repair — adhesion release followed by intensive therapy.