Flexor Tendon Injuries

Courtesy: Prof Nabil Ebraheim, University of Toledo, Ohio, USA

Overview

• Flexor tendon injuries involve trauma to the flexor digitorum superficialis and flexor digitorum profundus tendons.

• These injuries are commonly caused by lacerations or blunt trauma.

• They usually result from volar-sided injuries of the hand.

• Associated neurovascular injuries are common due to close anatomical proximity.

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Tendon Healing Mechanisms

Flexor tendon healing occurs through 2 pathways:

Intrinsic Healing

• Mediated by tenocytes within the tendon.

• Produces organized collagen and better tendon gliding.

• Preferred pathway for optimal functional recovery.

Extrinsic Healing

• Stimulated by surrounding synovial fluid and inflammatory cells.

• Contributes to scar formation and adhesions.

• Excessive extrinsic healing leads to restricted tendon motion.

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Causes of Flexor Tendon Injuries

• Sharp cut injuries.

• Sports-related injuries:

  • Jersey finger

  • Mallet finger

• Rheumatoid arthritis:

  • Rupture of flexor pollicis longus is the most common flexor tendon rupture.

• Attritional rupture due to malunited fractures of the distal radius or metacarpals.

• Bite injuries:

  • Extensor tendons are more commonly involved, but flexor tendons may also be affected.

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Flexor Zones of the Hand

• Flexor tendon injuries are classified based on anatomical zones of the hand.

• Zone-based classification guides prognosis, repair technique, and rehabilitation strategy.

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Blood Supply of Flexor Tendons

Synovial Diffusion

• Occurs when tendons are located within synovial sheaths.

• Primary source of nutrition distal to the metacarpophalangeal joint.

Direct Vascular Perfusion

• Supplies tendons outside synovial sheaths.

• Provided by:

  • Vincular system

  • Osseous insertions

  • Reflected vessels from tendon sheath

  • Longitudinal vessels from the palm

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Clinical Presentation

Symptoms

• Loss of active flexion strength.

• Inability to flex the involved digit or digits.

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Physical Examination

Inspection

• Observe resting posture of the hand and digital cascade.

• Malalignment or malrotation may indicate an associated fracture.

• Inspect skin integrity to localize tendon injury.

• Look for evidence of traumatic joint penetration.

Motion Assessment

• Passive wrist flexion and extension to assess the tenodesis effect.

• Normally, wrist extension produces passive flexion of the fingers at:

  • Metacarpophalangeal joints

  • Proximal interphalangeal joints

  • Distal interphalangeal joints

• Persistence of finger extension during wrist extension suggests tendon discontinuity.

• Active flexion of proximal and distal interphalangeal joints should be tested individually.

Neurovascular Examination

• Mandatory due to close relationship between flexor tendons and digital neurovascular bundles.

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Imaging

• Radiographs:

  • To identify associated fractures.

• Ultrasonography:

  • Useful for detecting tendon lacerations and discontinuity.

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Treatment

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Nonoperative Management

• Indicated for partial tendon lacerations involving less than 60% of tendon width.

• Consists of:

  • Wound care

  • Early controlled range of motion

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Indications for Tendon Reconstruction

• Failed primary tendon repair.

• Chronic untreated flexor tendon injuries.

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Flexor Digitorum Superficialis Transfer to the Thumb

• Single-stage procedure.

• Indicated for chronic rupture of flexor pollicis longus.

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Flexor Tendon Repair

Indications

• Laceration greater than 75% of tendon width.

• Laceration between 50% and 60% with triggering.

• Partial lacerations without triggering can be treated with epitendinous repair alone.

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Principles of Flexor Tendon Repair

• Repair should be performed within 10 to 14 days of injury.

• Core suture combined with epitendinous suture is recommended.

• Optimal repair uses 4 to 6 strands.

• Strickland modification of the Kessler technique is commonly used.

• Repair sequence:

  • Dorsal epitendinous sutures

  • Core sutures

  • Volar epitendinous sutures

• Minimal gapping at the repair site is essential.

• Repair failure most commonly occurs at the knot.

• Circumferential epitendinous sutures:

  • Increase repair strength by up to 50%

  • Reduce gap formation

• Larger suture diameter increases repair strength:

  • Nonabsorbable sutures of size 3 or 4 are preferred.

• Locking suture techniques do not significantly improve repair strength.

• Wide Awake Local Anesthesia No Tourniquet technique allows real-time assessment of repair integrity.

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Timing of Repair

• Ideal timing is within 2 weeks of injury.

• Repair should not be delayed beyond 3 weeks.

• Delayed repair leads to tendon retraction and increased technical difficulty.

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Surgical Approach

• Skin incisions should cross flexion creases transversely or obliquely.

• Longitudinal incisions should be avoided to prevent contractures.

• Atraumatic tendon handling is essential to minimize adhesion formation.

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Repair Techniques

• Core tendon sutures.

• Circumferential epitendinous sutures.

• Tendon sheath repair when possible.

• Pulley preservation or reconstruction.

• Repair of flexor digitorum superficialis when indicated.

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Flexor Tendon Reconstruction

Prerequisites

• Supple skin.

• Sensate digit.

• Adequate vascularity.

• Full passive range of motion of adjacent joints.

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Reconstruction Techniques

Single-Stage Reconstruction

• Indicated when the flexor sheath is intact and digit has full range of motion.

Two-Stage Reconstruction

Hunter–Salisbury Technique

• Stage 1:

  • Placement of silicone rod to create a pseudosheath.

• Stage 2 (after 3 to 4 months):

  • Removal of silicone rod.

  • Placement of tendon graft through pseudosheath.

  • Pulvertaft weave proximally.

  • End-to-end tendon repair distally.

Paneva–Holevich Technique

• Stage 1:

  • Silicone rod placement.

  • Pulley reconstruction if required.

  • Creation of loop between proximal flexor digitorum superficialis and flexor digitorum profundus stumps in the palm.

• Stage 2:

  • Removal of silicone rod.

  • Proximal flexor digitorum superficialis is divided and advanced distally.

  • Tendon is attached to distal flexor digitorum profundus stump or secured using a button.

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Graft Selection

• Palmaris longus tendon (absent in approximately 15% of population).

• Plantaris tendon (absent in approximately 19%).

• Extensor digitorum longus to second to fourth toes.

• Extensor indicis proprius.

• Flexor digitorum longus to second toe.

• Flexor digitorum superficialis tendon.

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Pulley Reconstruction

• At least one pulley should be reconstructed proximal and distal to each joint.

• Pulley reconstruction should be performed before tendon graft placement when reconstruction is planned.

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Postoperative Rehabilitation

• Controlled mobilization is the most important factor in improving outcomes after flexor tendon repair.

• Especially critical for zone 2 injuries.

• Benefits include:

  • Improved tendon healing biology

  • Reduced adhesion formation

  • Increased tendon excursion

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Rehabilitation Protocols

Immobilization

• Indicated for children and noncompliant patients.

• Casts or splints position:

  • Wrist and metacarpophalangeal joints in flexion

  • Interphalangeal joints in extension

Early Passive Motion

Duran Protocol

• Low force and low excursion.

• Active finger extension with patient-assisted passive flexion using static splint.

Kleinert Protocol

• Low force and low excursion.

• Active finger extension with dynamic splint-assisted passive flexion.

Mayo Synergistic Splint

• Low force and high tendon excursion.

• Incorporates active wrist motion to maximize tendon excursion.

Early Active Motion

• Moderate force with potentially high excursion.

• Uses dorsal blocking splint.

• Includes “place-and-hold” finger exercises.

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Complications

• Tendon adhesions:

  • Most common complication.

  • Higher incidence in zone 2 injuries.

  • Managed with therapy or tenolysis after 4 to 6 months if motion remains restricted.

• Tendon rerupture:

  • Reported rate of 15% to 25%.

• Joint contractures:

  • Occur in up to 17% of cases.

• Swan-neck deformity.

• Trigger finger.

• Lumbrical plus finger.

• Quadrigia effect.