Residency · Residency · Orthopedic Surgery

Flexor Tendon Injuries: Zones, Repair, and Rehabilitation

Overview

Flexor tendon injuries are among the most technically demanding hand surgery procedures. The goal is to restore smooth gliding of the tendon within the fibro-osseous sheath while achieving sufficient repair strength to allow early motion. Understanding zone anatomy, repair biomechanics, and rehabilitation protocols is essential for optimal outcomes.

Anatomy

Flexor Tendons of the Hand

The flexor digitorum superficialis (FDS) inserts on the middle phalanx via the Camper chiasm and flexes the PIP joint. The flexor digitorum profundus (FDP) passes through the FDS decussation, inserts on the distal phalanx, and flexes the DIP joint. The flexor pollicis longus (FPL) is the sole flexor of the thumb IP joint.

Fibro-Osseous Sheath and Pulley System

The annular pulleys are designated A1 (MCP), A2 (proximal phalanx), A3 (PIP), A4 (middle phalanx), and A5 (DIP). The cruciate pulleys (C1, C2, C3) sit between the annular pulleys and allow flexion. The A2 and A4 pulleys are critical and must be preserved or reconstructed to prevent bowstringing. The pulley system converts linear tendon excursion to angular joint motion.

Tendon Nutrition

Tendons receive a dual blood supply from the vincular system (vincula longa and brevia) and synovial fluid diffusion. In "no man's land" (Zone II), tendon nutrition is most tenuous, demanding the highest technical precision during repair.

Verdan Zone Classification

Zone I extends distal to the FDS insertion (FDP only). Zone II spans from the A1 pulley to the FDS insertion ("no man's land"), where both the FDS and FDP coexist in the sheath. Zone III is the palm (lumbrical origin to distal carpal tunnel). Zone IV is the carpal tunnel. Zone V is the forearm proximal to the carpal tunnel. Thumb zones are designated T1 (distal to IP), T2 (A1 pulley to IP), and T3 (thenar eminence).

<image>Verdan zone classification of flexor tendon injuries with pulley system anatomy</image>

Clinical Evaluation

History

Key history includes the mechanism (laceration from glass or knife, closed avulsion as in jersey finger), hand dominance, occupation, hobbies, prior hand injuries, and timing of injury since primary repair is ideally performed within 2 weeks.

Physical Examination

The FDP test holds the PIP in extension and asks the patient to flex the DIP. The FDS test holds all other fingers in extension (neutralizing the FDP via the quadriga effect) and asks the patient to flex the PIP. Loss of the normal resting cascade suggests tendon discontinuity. The digital Allen test assesses vascular status, and two-point discrimination evaluates for digital nerve injury, which is commonly associated.

Jersey Finger (FDP Avulsion)

The Leddy and Packer classification describes Type I where the tendon retracts into the palm (vincular disruption) requiring repair within 7-10 days, Type II where the tendon retracts to the PIP level (vincula intact) allowing repair within weeks, Type III with a large bony avulsion at the DIP that does not retract significantly and may be repaired later, and Type IV (Smith modification) with a bony fragment plus tendon avulsion from the bone fragment.

Repair Techniques

Core Suture Principles

Repair strength is proportional to the number of strands crossing the repair site: a 2-strand repair achieves approximately 20-30 N, a 4-strand repair 40-50 N, and a 6-strand repair 60-70 N. A minimum 4-strand repair is recommended for early active motion protocols. Suture caliber is typically 3-0 or 4-0 braided polyester or polyfilament. Core purchase should be at least 7-10 mm from the cut edge, and locking loops are stronger than grasping loops.

Common Core Suture Techniques

The modified Kessler is a 2-strand locking technique. The cruciate (cross-stitch) provides 4 strands. The Savage (6-strand) is stronger but technically demanding. The Adelaide (Lim-Tsai) may be configured as 4-strand or 6-strand.

Epitendinous Suture

A running simple or locking horizontal mattress suture (6-0 nylon) adds 10-50% to repair strength, smooths the repair surface to reduce friction and improve gliding, and is an essential component that should never be omitted.

Zone-Specific Considerations

In Zone I, FDP advancement and repair to bone uses a pull-out suture or suture anchor; advancement is limited to less than 1 cm to avoid the quadriga effect. Zone II is the most technically challenging with both tendons within the sheath. The FDP is repaired; historically the FDS was excised, but current practice favors repairing at least one slip of FDS when possible to improve PIP flexion strength. The A2 and A4 pulleys must be preserved, though one pulley (A3 or A4) may be vented for access. Zones III-V generally have a better prognosis because there is more room for repair and tendon nutrition is superior; associated nerve and vessel injuries may need to be addressed.

<image>Four-strand cruciate core suture technique for flexor tendon repair with epitendinous suture</image>

Rehabilitation Protocols

Principles

Rehabilitation must balance protecting the repair against preventing adhesion formation. Tendon repairs are weakest at 5-12 days post-repair before biologic healing contributes. Controlled motion promotes intrinsic tendon healing and reduces adhesions.

Protocol Options

Passive Motion (Duran/Modified Kleinert)

A dorsal blocking splint with the wrist in approximately 20 degrees of flexion and MCP joints at 50-70 degrees of flexion is used. Rubber band traction (Kleinert) or therapist-directed passive flexion/extension protects the repair while preventing adhesions. This protocol has a lower re-rupture rate but higher adhesion rate compared to active protocols.

Early Active Motion (Place-and-Hold / Active Flexion)

This protocol requires a strong repair (minimum 4-strand core suture). The patient actively extends fingers within the dorsal blocking splint, then passively flexes and holds with active muscle contraction. A synergistic wrist motion protocol couples wrist extension with finger flexion and wrist flexion with finger extension. This approach produces better outcomes (ROM, grip strength) than pure passive protocols but requires a compliant patient and experienced hand therapist.

True Active Motion (Immediate Active Flexion)

The most aggressive protocol requires a 6-strand repair with epitendinous suture. It is reserved for centers with strong hand therapy programs and produces the lowest adhesion rates but carries the highest re-rupture risk if the repair or patient compliance is suboptimal.

General Timeline

Weeks 0-4 involve protected motion (passive or early active within the splint). Weeks 4-6 allow gradual splint weaning and gentle active flexion/extension. Weeks 6-8 introduce progressive strengthening. Weeks 8-12 permit unrestricted activity.

<image>Dorsal blocking splint positioning for flexor tendon rehabilitation with early active motion protocol</image>

Complications

Adhesion Formation

Adhesion formation is the most common complication. Risk factors include Zone II injuries, crush mechanisms, associated fractures, delayed repair, and prolonged immobilization. Treatment begins with hand therapy; tenolysis is considered if progress plateaus after 3-6 months. Tenolysis requires a minimum of 3 months after repair, full passive ROM before surgery, and is performed under local or wide-awake anesthesia so the patient can actively demonstrate tendon excursion.

Rupture

The incidence of rupture is 3-10% with modern techniques and protocols, occurring most commonly in the first 2 weeks. Risk factors include fewer core strands, overly aggressive rehabilitation, and noncompliant patients. Early ruptures may be re-repaired; late failures require staged reconstruction with a silicone rod followed by tendon graft.

Staged Tendon Reconstruction (Hunter Rod)

For failed primary repair, chronic injuries, or severely scarred tendon beds, a two-stage reconstruction is performed. In Stage 1, a silicone rod is placed through the sheath to create a pseudosheath, with pulley reconstruction if needed. In Stage 2 (3-6 months later), the rod is removed and a free tendon graft (palmaris longus, plantaris, or long toe extensor) is threaded through the pseudosheath.

Clinical Pearls

Wide-awake local anesthesia no tourniquet (WALANT) allows intraoperative assessment of repair gliding and active motion and is increasingly popular for flexor tendon repair. Associated digital nerve injury is found in 30-50% of flexor tendon lacerations and must always be evaluated. Partial tendon lacerations involving more than 60% of tendon width should be repaired (core suture plus epitendinous); less than 25% can be trimmed; 25-60% is surgeon preference. FDP should not be advanced more than 1 cm to avoid the quadriga effect (limited excursion of adjacent fingers due to the shared FDP muscle belly). The lumbrical-plus finger occurs when the FDP is lacerated and the FDS is intact; attempted DIP flexion paradoxically extends the PIP via the lumbrical, which can be clinically confusing. Documentation should always record the exact zone, which tendons are injured, and any associated neurovascular injury.

References

• Verdan CE. Primary repair of flexor tendons. JBJS Am. 1960;42(4):647-657.
• Strickland JW. Development of flexor tendon surgery. J Hand Surg Am. 2000;25(2):214-235.
• Leddy JP, Packer JW. Avulsion of the profundus tendon insertion in athletes. J Hand Surg Am. 1977;2(1):66-69.
• Tang JB. Recent developments in flexor tendon repair. J Hand Surg Am. 2018;43(11):991-999.
• Starr HM, Snoddy M, Hammond KE, Seiler JG. Flexor tendon repair rehabilitation protocols: a systematic review. J Hand Surg Am. 2013;38(9):1712-1717.

Read this lecture as Markdown