Comprehensive Study Guide for Flexor Tendon Repair and Reconstruction

Overview of Flexor Tendon Repair and Reconstruction

• Goal of Treatment: Regaining satisfactory digital function after a flexor tendon laceration remains a complex challenge in hand surgery, requiring deep histology and biomechanics knowledge to optimize outcomes.

• Historical Context:

  • Era of Neglect: Second-century physician Galen argued against repair, fearing convulsions and death. This dogma persisted until the 17th century, despite Avicenna recommending acute repair in the 10th century.

  • Era of Repair: Initiated after Haller (1752) proved repair was safe. Early writing by Bunnell (1944) highlighted the difficulty of restoring normal function due to fibrosis.

  • Era of Early Mobilization: Researchers like Viering, Bunnell, Mason, and Allen demonstrated that motion influences tendon healing and synovial membrane formation. Mason and Allen (1941) showed protected motion improved repair strength over total immobilization.

  • Era of Immediate Controlled Mobilization: This era began with Kleinert's protocol (immediate protected motion) and the Duran and Houser protocol ($3$ to $5\,mm$ of passive motion). Gelberman later proved that passive mobilization increases tensile strength and excursion within the digital sheath.

Anatomy and Biology of Flexor Tendons

• Tendon Structure: Each digit has two flexor tendons:

  • Flexor Digitorum Superficialis (FDS): Splits at the metacarpophalangeal (MCP) joint level (Chiasma of Camper) to allow the FDP to pass through.

  • Flexor Digitorum Profundus (FDP): Becomes superficial to the FDS distal to the chiasma.

• Pulley System: A fibrous sheath extending from the metacarpal neck to the distal phalanx base, containing annular ($A1$ to $A5$) and cruciate ($C1$ to $C3$) pulleys.

  • Finger Vitality: $A2$ and $A4$ pulleys (overlying proximal and middle phalanges) are the most functionally significant for preventing bowstringing.

  • Thumb Pulleys: Consist of $A1$ (MCP joint), $A2$ (IP joint), and the Oblique pulley, which is an extension of the adductor pollicis aponeurosis and critical for FPL function.

• Nutrition and Healing:

  • Vascularity: Received via intratendinous vessels and vascular networks called vincula ($Vinculum Longus$ and $Vinculum Brevis$). Repairing both FDS and FDP in Zone II preserves the vincular communication maintaining FDP nutrition.

  • Healing Mechanisms:

    • Intrinsic: Tenocytes within the tendon bridge the gap.

    • Extrinsic: Fibroblasts from surrounding tissue proliferate, often leading to adhesions.

  • Early Mobilization: Essential for promoting intrinsic over extrinsic healing, thereby reducing adhesions.

• Biomechanics: The gliding interface has a friction coefficient similar to articular cartilage. Friction increases with knots on the surface or braided sutures; monofilament is preferred.

Flexor Tendon Zones

• Zone I: Distal to FDS insertion, containing only the FDP.

  • Sub-zone IA: < 1\,cm of FDP stump; requires reattachment to bone (advancement).

  • Sub-zone IB: > 1\,cm of stump beyond A4; allows end-to-end repair.

  • Sub-zone IC: Underneath the A4 pulley.

• Zone II (No Man’s Land): Within the narrow flexor sheath from FDS insertion to the A1 pulley.

  • Sub-zone IIA: FDS insertion area.

  • Sub-zone IIB: Area between FDS insertion and A2 distal margin.

  • Sub-zone IIC: Underneath A2 pulley.

  • Sub-zone IID: Proximal margin of A2 to proximal A1.

• Zone III: From A1 to the distal edge of the flexor retinaculum; lumbricals originate here.

• Zone IV: Within the carpal tunnel under the flexor retinaculum.

• Zone V: Proximal to the flexor retinaculum, including muscle-level injuries.

  • Sub-zone VA: Tendinous portion in the forearm.

  • Sub-zone VB: Muscular part distal to nerve supply entry.

  • Sub-zone VC: Proximal muscle near nerve entry.

• Thumb Zones:

  • TI: Fingertip to proximal phalanx neck (FPL insertion).

  • TII: Proximal phalanx neck to A1 pulley.

  • TIII: A1 pulley to flexor retinaculum.

Diagnosis and Initial Evaluation

• Clinical Presentation: The injured finger loses its normal flexion cascade and remains relatively extended.

• Tenodesis Test: Passive wrist extension should cause finger flexion; lack of flexion indicates injury.

• Specific Tests:

  • FDS: Tested by blocking the FDP of other fingers (since FDP for middle, ring, and little fingers share a common muscle belly).

  • FDP: Tested via DIP joint flexion while stabilizing the PIP joint.

• Partial Injury: Indicated by pain on resisted flexion even if active flexion is possible. Injuries involving < 50\% usually require only trimming; > 50\% require repair.

• Imaging: Ultrasound is used to localize retracted tendon ends or verify repair integrity.

Surgical Management and Suturing

• Objectives: Strength for early mobilization without gap formation. Forces during active mobilization can reach $\approx 120\,N$.

• Suture Techniques:

  • Core Suture: Provides primary strength. Modern protocols require a minimum of $4$ to $6$ strands crossing the repair site to support active motion.

  • Circumferential (Epitendinous) Suture: Smoothens the surface and adds strength. Techniques include simple running or crisscross locking sutures.

• Suture Properties:

  • Caliber: Core sutures typically $3-0$ or $4-0$; peripheral are $5-0$ or $6-0$. $3-0$ is significantly stronger.

  • Purchase: Minimum length from the cut end is $7\,mm$; $10\,mm$ is optimal. Loops should have a $2\,mm$ bite.

  • Material: Non-absorbable synthetic options like Prolene, Ethibond, or high-strength FiberWire.

  • Tension: Tang recommends $10\%$ extra tensioning to resist gapping (> 3\,mm gap results in low strength).

• Incision: Brunner’s zigzag or midlateral exposure. Midlateral prevents scar/tendon overlap.

• Pulley Management: Efforts to preserve A2 and A4 are critical. Partial venting is allowed: up to $25\%$ of A2 and $75\%$ of A4.

Timing of Repair

• Primary Repair: Within $24$ hours.

• Delayed Primary: $24$ hours to $10$ days. Outcomes up to $5$ days are identical to primary repair.

• Secondary Repair: Between $10$ days and $4$ weeks.

• Late Secondary: After $4$ weeks.

Postoperative Rehabilitation Protocols

• Immobilization: Reserved for children or non-compliant patients ($3$ to $4$ weeks).

• Early Passive Mobilization:

  • Kleinert’s Protocol: Posterior splint with dynamic rubber band traction; active extension with passive flexion.

  • Duran-Houser Protocol: Manual passive movement of DIP and PIP joints twice daily ($3$ to $5\,mm$ excursion).

  • Washington Protocol: Uses two sources of traction and a palmar pulley.

• Early Active Mobilization: Required for repairs with $4$ or more strands (e.g., Strickland’s or Gratton’s protocols). Higher risk of rupture but superior motion outcomes.

• Outcome Assessment: Strickland’s Method uses total active range of motion at interphalangeal joints:

  • Excellent: > 150^{\circ}

  • Good: $125^{\circ}$ to $149^{\circ}$

  • Fair: $90^{\circ}$ to $124^{\circ}$

  • Poor: < 90^{\circ}

Complications

• Rupture: Most common in the first $2$ weeks ($6$ to $12$ days). Detection via loss of flexion power or tone. Re-exploration and repair required.

• Adhesions: Characterized by limited active but full passive movement. If therapy fails, Tenolysis is indicated after $3$ to $6$ months.

• Quadriga Effect: Inability to flex uninjured fingers due to excessive tension in a repaired FDP tendon (common muscle belly issue).

• Lumbrical Plus Deformity: Paradoxical IP extension during flexion attempts; caused by a too-loose FDP graft.

• Joint Contractures: Preventable with proper split positioning and IP joint stretching.

Secondary Reconstruction and Closed Injuries

• Two-Stage Reconstruction:

  • Stage 1: Silicone rod placement to create a pseudosheath and pulley reconstruction.

  • Stage 2: Replacing the rod with a tendon graft (Palmaris longus, Plantaris, or FDS) $3$ to $6$ months later.

• Pulley Reconstruction: Treated via encircling grafts if the fibrous rim is absent, or suturing to remnants if present.

• Jersey Finger (Closed FDP Rupture): Common in the ring finger from forceful extension against active flexion.

  • Leddy and Packer Classification:

    • Type I: Retracted to palm.

    • Type II: Retracted to PIP joint.

    • Type III: Avulsed bony fragment at A4.

    • Type IV: Retracted to palm with avulsed bone at A4.

    • Type V: Bony fragment at A4 with concomitant distal phalanx fracture.

  • Management: Reinsertion via bone tunnels and buttons or suture anchors. Type I must be treated within $10$ days to avoid myostatic contracture.

Questions & Discussion

• Q: Should both FDS and FDP be repaired in Zone II?

  • A: Modern expert consensus favors repairing both in clean injuries to improve vascularity (vincula) and independent flexion, provided the surgeon is skilled enough to avoid excess volume in the sheath.

• Q: What is the benefit of Wide-Awake Local Anesthesia No Tourniquet (WALANT)?

  • A: It allows the surgeon to assess the gliding of the repair site through the pulleys in real-time, ensuring no gapping or triggering occurs before closing the wound.