Tarsocrural (hock) luxation or subluxation is a high-grade ligamentous injury involving disruption of the medial and/or lateral collateral ligaments, frequently accompanied by capsular tearing and soft-tissue damage. These injuries are typically the result of shearing trauma, vehicular accidents, or significant hyperextension forces, and are biomechanically equivalent to a Grade 3 sprain with complete ligament rupture or avulsion.

The tarsocrural joint is a low-profile, high-motion hinge joint, and stability depends primarily on the pair of collateral ligaments—each composed of a long and short portion. These structures guide and limit motion throughout the entire range of flexion and extension. When disrupted, they create pronounced valgus or varus instability, often accompanied by rotational malalignment.

Surgical stabilization is indicated in all high-grade injuries, as conservative management leads to permanent instability, chronic pain, and progressive degenerative joint disease (DJD).

1. Diagnosis and Biomechanical Implications

Clinical Examination

Classic findings include:

• Valgus instability → medial collateral ligament (MCL) rupture

• Varus instability → lateral collateral ligament (LCL) rupture

• Joint effusion, swelling, and resistance to weight-bearing

The MCL is injured more frequently and is more biomechanically significant because it resists valgus forces generated during stance.

Imaging

• Stress radiography (varus/valgus stress views) confirms collateral ligament insufficiency.

• CT or MRI may be considered for complex shearing injuries to assess articular surface involvement.

Correct identification of the injured long vs. short fibers is essential, as each component stabilizes different joint positions. Without anatomical reconstruction of both, instability persists even if the joint appears aligned at rest.

2. Surgical Objectives

The primary surgical goals are:

1. Restore anatomic alignment and joint congruity

2. Reconstruct the long and short portions of the affected collateral ligament

3. Provide temporary rigid immobilization to permit soft-tissue healing

4. Prevent long-term instability and minimize the development of DJD

Ligament repair alone is insufficient; a temporary external stabilizing device is essential to protect the reconstruction.

3. Ligament Reconstruction Techniques

A. Primary Ligament Repair

Indicated when avulsed or torn fibers are repairable.

Techniques include:

• Imbrication of capsule and ligament remnants

• Suturing or reattaching avulsed fragments

• Reconstructing both long and short components independently

Suture material:

• Nonabsorbable braided polyester

• Heavy monofilament nylon

Repair should be performed with the hock held in a neutral standing angle (135–145°) to reproduce normal isometry.

B. Synthetic Ligament Augmentation

Most cases—especially shearing injuries—require augmentation or full replacement of the ligament.

Implant options:

1. Heavy braided polyester sutures (e.g., FiberTape, Ethibond)

2. Monofilament nylon leader line

3. Bone anchors, screws with washers, or tunnel techniques for bony fixation

Correct anchor placement is crucial. Synthetic ligament pathways must follow physiologic isometric points; otherwise, the reconstruction will bind or slacken during flexion, leading to joint overconstraint or persistent instability.

C. Irreparable or Severe Injuries

Chronic instability, massive shearing loss, or severe articular damage may require primary tarsocrural arthrodesis.
Indications include:

• Significant cartilage loss

• Unreconstructable ligamentous structures

• Severe bone loss or contamination

Arthrodesis is typically performed at 135–145° for functional limb position.

4. Temporary Immobilization: Essential for Success

No ligament repair—primary or synthetic—can withstand the mechanical load of the hindlimb during early healing. Protection is required for 6–8 weeks.

Preferred method: Transarticular External Skeletal Fixator (TESF)

Benefits:

• Rigid immobilization

• Adjustable alignment

• Effective protection of soft-tissue repairs

TESF must be applied with the hock positioned at physiologic extension (135–145°).

Alternative: Splint or Cast

A splint or cast alone is insufficient for Grade 3 injuries.
However, splinting can be used as adjunctive support after TESF removal or when ESF is contraindicated.

5. Postoperative Management

A. Immobilization

Maintain TESF or splint-based external support for 6–8 weeks, depending on healing progression and stability.

B. Activity Restriction

• Strict confinement

• Short, controlled leash-only walks for toileting

• No running, jumping, or uneven surfaces

C. Wound Monitoring

Owners should check the limb twice daily.
Alert signs include:

• Redness

• Discharge

• Foul odor

• Excessive swelling

• Self-trauma

A recovery collar is mandatory until incisions are fully healed.

D. Rehabilitation

After external support removal:

• Gradual increase in activity beginning at 10–12 weeks

• PROM exercises early to maintain mobility but avoid stressing the repair

• Hydrotherapy (underwater treadmill or swimming) for controlled strengthening with minimal load

• Avoid high-impact activities for several months

6. Prognosis and Long-Term Considerations

With appropriate reconstruction, immobilization, and rehabilitation, functional outcomes are generally good to excellent.
However:

• Some degree of DJD is expected in most cases

• Working and athletic dogs may not return to full performance

• Malalignment or improper isometric placement of synthetic ligaments leads to chronic instability

Success depends on:

• Accuracy of ligament reconstruction

• Quality of immobilization

• Early detection of complications

• Client adherence to postoperative protocols
  
  FAQ: Tarsocrural Luxation Repair (Collateral Ligament Reconstruction)

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  1. What is the most important stabilizer of the tarsocrural joint?

  The medial and lateral collateral ligaments—each with long and short components—are the primary stabilizers throughout the full range of flexion and extension.
  The medial collateral ligament (MCL) is biomechanically more critical because it resists valgus forces encountered during stance.

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  2. Why does ligament repair alone fail without temporary immobilization?

  Even perfectly reconstructed ligaments cannot withstand normal tension loads in the early healing period.
  A transarticular ESF (TESF) or rigid external support is required for 6–8 weeks to protect the repair and prevent cyclic stretching or catastrophic failure.

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  3. How do I determine which collateral ligament structures are damaged?

  Perform valgus/varus stress radiography and palpation under anesthesia.
  Remember:

  • Long component → stabilizes in extension

  • Short component → stabilizes in flexion
    Both must be reconstructed to restore stability.

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  4. When should synthetic ligament augmentation be used?

  Synthetic augmentation is indicated when:

  • Primary tissue is insufficient for repair

  • Shearing injuries create significant soft-tissue loss

  • Tissue quality is poor or frayed

  • Avulsion fragments are missing

  Materials include braided polyester (e.g., FiberTape) and monofilament nylon, anchored with screws + washers or bone anchors.

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  5. How do I locate proper isometric points for synthetic ligament placement?

  Isometric points should maintain consistent tension throughout flexion and extension.
  Misalignment results in:

  • Overconstraint (tight in extension, loose in flexion)

  • Abnormal joint biomechanics

  • Early onset DJD

  • Implant failure

  Correct positioning must mimic the orientation of native long and short components.

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  6. When is primary arthrodesis indicated?

  Arthrodesis is recommended when:

  • There is severe articular cartilage destruction

  • Soft tissue is irreparable (e.g., severe shearing injuries)

  • Bone stock is insufficient for ligament reconstruction

  • Chronic instability or failed repair is present

  Target angle: 135–145° for functional limb position.

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  7. What is the preferred method for temporary joint immobilization?

  A transarticular external skeletal fixator (TESF) is the gold standard.
  Advantages:

  • Rigid immobilization

  • Alignment control

  • Adjustability

  • Superior protection during the first 6–8 weeks of healing

  Splints or casts may be used as adjunctive support—but not as the primary stabilizer.

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  8. What complications are most common after tarsocrural luxation repair?

  • Persistent instability due to improper reconstruction

  • Stretching or failure of synthetic implants

  • DJD progression

  • Malalignment from improper TESF positioning

  • Soft-tissue complications related to shearing wounds

  • Infection, especially in open or contaminated injuries

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  9. When can rehabilitation begin?

  PROM exercises may begin early, as long as no stress is placed on the repair.
  Full rehabilitation (including hydrotherapy) begins after TESF removal, typically around 8–10 weeks.

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  10. What factors most influence prognosis?

  • Precision of ligament reconstruction

  • Correct identification of long vs. short fiber damage

  • Proper isometric placement of synthetic augmentation

  • Adequate immobilization

  • Client compliance

  Outcomes are generally good, though mild DJD is expected in most cases.