Residency · Residency · Plastic Surgery

Flexor Tendon Injuries and Repair

Overview

Flexor tendon injuries of the hand remain one of the most challenging problems in hand surgery. Outcomes depend on zone of injury, repair technique, rehabilitation protocol, and patient compliance. Advances in suture techniques and early active motion protocols have significantly improved functional results. ---

Flexor Tendon Zones

Verdan Classification (Fingers)

Thumb Zones

T1: distal to IP joint. T2: from A1 pulley to IP joint (critical zone analogous to Zone II). T3: thenar eminence.

Clinical Significance of Zones

Zone II historically had the worst outcomes ("no man's land") due to tendon adhesion within the fibro-osseous sheath. Zone I injuries involve only FDP and are technically simpler but have unique challenges (short distal stump). Zone III-V injuries generally have better outcomes due to absence of the restrictive sheath. ---

Tendon Anatomy and Biology

Structure

Collagen fibers (95% Type I) organized into fibrils, fibers, fascicles, and bundles. Epitenon: outer synovial lining that facilitates gliding. Endotenon: internal connective tissue that carries blood vessels. Mesotenon: attaches tendon to sheath wall.

Blood Supply

Vincular system: vincula longus and brevis provide segmental blood supply from digital arteries. FDS receives blood from vincula brevis superficialis and vincula longus superficialis. FDP receives blood from vincula brevis profundus and vincula longus profundus. Synovial diffusion: nutrients from synovial fluid within the sheath (accounts for 50% or more of tendon nutrition).

Healing Biology

Intrinsic healing: tenocytes within the tendon proliferate and produce collagen (preferred mechanism). Extrinsic healing: granulation tissue from the tendon sheath and surrounding tissue invades the repair site (leads to adhesions). Modern rehabilitation aims to promote intrinsic healing while minimizing extrinsic adhesion formation. Early motion stimulates intrinsic healing and produces a stronger repair. ---

Diagnosis and Evaluation

Clinical Examination

FDS test: hold all other fingers in full extension (blocks the shared FDP muscle belly), ask patient to flex the tested finger -- PIP flexion confirms FDS integrity. FDP test: stabilize the PIP joint in extension, ask patient to flex the DIP -- DIP flexion confirms FDP integrity. Tenodesis effect: passive wrist extension causes finger flexion, wrist flexion causes finger extension; absent tenodesis effect suggests complete tendon disruption. Cascade: normal resting cascade shows progressive flexion from index to small; disruption suggests tendon laceration.

Assessment Checklist

Neurovascular examination (digital nerves and arteries often injured concomitantly). Wound exploration in a controlled setting (do not probe in the emergency department). Radiographs to evaluate for fractures or foreign bodies. Document pre-repair range of motion and sensory status.

<image>Palmar view illustration of the hand showing the five flexor tendon zones (I-V) for the fingers and three zones (T1-T3) for the thumb. Each zone is color-coded and labeled with anatomical boundaries. An inset cross-section at Zone II level shows the FDP and FDS tendons within the flexor sheath surrounded by the A2 pulley, with the chiasm of Camper visible, the vincular blood supply from the digital arteries, and the digital nerves flanking the sheath.</image>

Surgical Repair Principles

Timing

Primary repair: within 12-24 hours (ideal). Delayed primary repair: up to 2-3 weeks (still acceptable results). Late reconstruction: >4 weeks; primary repair usually not possible; consider staged tendon reconstruction with Hunter rod.

Core Suture Techniques

General principle: more core suture strands = greater repair strength. Minimum 4-strand repair required for early active motion protocols.

Epitendinous Suture

Running circumferential suture along the repair site. Adds 10-50% additional strength to the repair. Smooths the repair surface to reduce gliding resistance. Commonly a simple running or running locking suture (6-0 nylon or Prolene).

Suture Material

Braided polyester (Ethibond, FiberWire) or monofilament (Prolene) -- 3-0 or 4-0 for core sutures. Higher caliber suture and braided material provide stronger repairs but increase bulk. Looped sutures (Supramid, FiberLoop) allow 4-strand repair from a single pass.

Technical Principles

Purchase >1 cm from the cut end on each side. Lock the core suture at each exit point (locking is stronger than grasping). Avoid excessive shortening (>5 mm gap increases repair failure risk). Minimize tendon handling to preserve the epitenon and vincula. Partial lacerations >60% should be repaired; <25% can be trimmed; 25-60% is judgment-based.

Pulley Management During Repair

Preserve A2 and A4 pulleys at all costs. A1, A3, and A5 can be partially or fully vented/released to allow tendon retrieval and repair. If A2 must be opened for access, it should be reconstructed. ---

Zone-Specific Considerations

Zone I (FDP Only)

Short distal stump makes core suture challenging. Options: direct repair (if sufficient stump), pullout button technique, bone anchor fixation. Advancement of FDP up to 1 cm is acceptable (>1 cm causes lumbrical plus or DIP quadriga).

Zone II (Critical Zone)

Both FDS and FDP within the sheath. Repair both tendons when possible (preserves independent PIP flexion). Some surgeons excise one slip of FDS if sheath is tight after repair of both tendons. Meticulous technique to minimize adhesions within the sheath.

Zone III (Palm)

Lumbrical origins may complicate repair. Generally easier repairs with better outcomes than Zone II. Repair associated neurovascular injuries (common digital nerves and arteries).

Zone IV (Carpal Tunnel)

Up to 9 tendons may be injured. Transverse carpal ligament should not be repaired after tendon repair (prevents carpal tunnel syndrome). Median nerve injury is common and should be repaired.

Zone V (Forearm)

Multiple structures at risk: flexor tendons, median nerve, ulnar nerve, radial and ulnar arteries. "Spaghetti wrist": 10+ structure injuries at the wrist level. Systematic identification and repair of all structures. ---

Rehabilitation Protocols

Duran Passive Motion Protocol

Passive flexion and active extension within a dorsal blocking splint. Wrist in 20 degrees flexion, MCP in 50 degrees flexion. Allows 3-5 mm of tendon excursion to prevent adhesions. Used for 2-strand repairs or less reliable patients.

Kleinert Protocol

Dynamic traction with rubber band from fingernail to wrist. Passive flexion via rubber band, active extension against the band. Risk of PIP flexion contracture from constant traction.

Early Active Motion (Place-and-Hold)

Active flexion within a controlled range (composite fist). Requires minimum 4-strand repair (preferably 6-strand). Produces stronger repairs with fewer adhesions. Gold standard protocol at most centers.

True Active Motion (Indiana Protocol)

Full active flexion against light resistance beginning day 3-5. Requires strong 6-8 strand repair. Best results in compliant patients with experienced hand therapists. Higher re-rupture rate if repair is inadequate.

General Rehabilitation Timeline

0-4 weeks: protected motion within dorsal blocking splint. 4-6 weeks: gradual weaning from splint, active motion exercises. 6-8 weeks: progressive resistive exercises. 8-12 weeks: full unrestricted activity. ---

Complications

Adhesion Formation

Most common complication, especially in Zone II. Presents as loss of differential gliding between FDS and FDP. Management: intensive hand therapy; tenolysis if therapy fails after 3-6 months. Tenolysis should not be performed until passive ROM exceeds active ROM significantly and the wound is supple.

Repair Rupture

Incidence: 4-10% (higher with early active motion and weak repairs). Most common in the first 10-14 days. Re-rupture usually requires re-exploration and repair or staged reconstruction.

Stiffness

Joint contracture (especially PIP flexion contracture). Prevention: early motion and proper splinting. Treatment: serial casting, dynamic splinting, capsulotomy if refractory.

Triggering

Can occur at pulley sites after repair. Usually due to bulk of the repair catching at A2 or A4. ---

Staged Tendon Reconstruction

Indications

Failed primary repair with extensive scarring. Delayed presentation (>4-6 weeks) with retracted tendon and scarred sheath. Severely damaged sheath and pulleys requiring reconstruction.

Stage 1

Insert a silicone Hunter rod through the reconstructed pulley system. Rod creates a pseudosheath (synovial-like lining) around itself over 2-3 months. Pulley reconstruction performed simultaneously.

Stage 2 (3-4 Months Later)

Remove the Hunter rod. Thread a free tendon graft (palmaris longus, plantaris, or toe extensor) through the pseudosheath. Attach distally to the distal phalanx and proximally by Pulvertaft weave to the motor tendon. Begin rehabilitation protocol.

<image>Two-panel medical illustration of staged flexor tendon reconstruction. Panel 1 (Stage 1): lateral view of a finger showing a silicone Hunter rod placed within the reconstructed flexor sheath, with reconstructed A2 and A4 pulleys, the rod attached distally to the distal phalanx. Panel 2 (Stage 2, 3 months later): the Hunter rod removed and replaced with a palmaris longus tendon graft threaded through the mature pseudosheath, with the graft secured distally to bone and proximally by Pulvertaft weave to the FDP motor in the forearm.</image>

Clinical Pearls

Zone II remains the most challenging zone for flexor tendon repair -- meticulous technique, strong core suture (minimum 4-strand), and early active motion are essential for good outcomes. The strength of a flexor tendon repair is directly proportional to the number of core suture strands crossing the repair site -- 4 strands minimum for early active motion, 6 strands preferred. Always examine digital nerve and artery function before repair -- concomitant neurovascular injury is common, especially in sharp lacerations. Avoid advancing the FDP more than 1 cm in Zone I -- excessive advancement causes the quadriga effect (limits excursion of adjacent FDP tendons) or the lumbrical-plus phenomenon.

The epitendinous suture is not optional -- it adds significant strength, smooths the repair, and reduces gap formation. Hand therapy is as important as the surgical repair -- outcomes depend on a compliant patient working with an experienced certified hand therapist. Tenolysis should only be performed after the wound is mature and supple (6+ months) and when passive ROM significantly exceeds active ROM. For staged reconstruction, the pseudosheath formed around the Hunter rod is biologically analogous to a native tendon sheath and must be handled gently. ---.

References

• Strickland JW. Development of flexor tendon surgery: twenty-five years of progress. J Hand Surg Am. 2000;25(2):214-235.
• Tang JB. Indications, methods, postoperative motion and outcome evaluation of primary flexor tendon repairs in Zone 2. J Hand Surg Eur Vol. 2007;32(2):118-129.
• Winters SC, Gelberman RH, Woo SL, et al. The effects of multiple-strand suture methods on the strength and excursion of repaired intrasynovial flexor tendons. J Hand Surg Am. 1998;23(1):97-104.
• Kleinert HE, Kutz JE, Atasoy E, Stormo A. Primary repair of flexor tendons. Orthop Clin North Am. 1973;4(4):865-876.
• Hunter JM, Salisbury RE. Flexor-tendon reconstruction in severely damaged hands. J Bone Joint Surg Am. 1971;53(5):829-858.
• Peck FH, Bucher CA, Watson JS, Roe A. A comparative study of two methods of controlled mobilization of flexor tendon repairs in Zone 2. J Hand Surg Br. 1998;23(1):41-45.

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