Revision Total Knee Replacement

Most Important Factor:

  • Accurate diagnosis of the cause of failure and a clear strategy for revision.

Causes of Failure:

  1. Osteolysis
  2. Aseptic Loosening
  3. Catastrophic Polyethylene (PE) Failure
  4. Patella Pain
  5. Instability
  6. Fracture
  7. Infection
  8. Stiffness
  9. Undiagnosed (Mystery Knee)

Osteolysis

  • Less common in TKR.
  • Wear mode in TKR: subsurface delamination.
  • Delamination produces larger particles compared to abrasive wear, which are more biologically active.
  • When osteolysis occurs in TKR, it tends to be expansile.

Aseptic Loosening

  • Less common cause than wear.
  • Tibia is more commonly affected than the femur.
  • Uncemented designs are prone to early loosening but become equal thereafter.
  • May be related to osteolysis but not always.
  • Malalignment (especially varus) predisposes to loosening.
  • Diagnosis:
    • New onset pain (e.g., start-up, weight-bearing, knee motion).
    • Subsidence of tibia.
    • Changes in tibial position or rotation.
    • Radiolucent lines that progress in size or are continuous.
    • Stiffness.

Stiffness

  • Can be global (failure to extend or flex).
  • Arthrofibrosis (scarring, especially in medial and lateral recesses) causes global stiffness.
  • Loss of extension: Often due to hamstring overactivity or overstuffing of the extension gap.
  • Loss of flexion: Due to quadriceps contracture or overstuffing of the flexion gap.
  • Manipulation under anesthesia (MUA) should be performed within 6 weeks; overstuffing requires revision.

Instability

  • Types: Mediolateral, patella, and flexion instability.
    • Mediolateral Instability: Caused by collateral ligament injury, intra- or post-operatively.
    • Flexion Instability: Typically, the knee sits backward due to absence of ACL. Worse with tight or strong hamstrings.
      • Paradoxical anterior femoral translation instead of rollback.
    • Patella Instability: Usually due to component malrotation.

Evaluating the Painful Knee

  • History, imaging, and blood tests are essential.
  • Three broad causes:
    1. Infection/inflammation
    2. Neurogenic
    3. Mechanical
  • Mechanical Causes:
    • Patella: Clunk syndrome (scar tissue impinging against the polyethylene post in a PS knee).
    • Flexion Instability: Associated with anterior translation of femur in CR knees.
    • Malalignment: Varus causes loosening; valgus causes instability.

Assessment of Bone Loss

  • Pre-operative imaging may underestimate bone loss.
  • CT scan and intra-operative assessment are better.
  • Factors: Size, location, contained or uncontained defects, and potential blood supply to the bone.
  • Surgical Principles: Diagnosis, exposure, bone loss, instability, joint line height.

Approach & Exposure

  • In multiply operated knees, use the most lateral incision to avoid anterior skin necrosis.
  • Medial Parapatellar approach is commonly used.
  • Extensile measures: Rectus snip, tibial tubercle osteotomy (avoided if possible).

Bone Loss Management

  • Small defects: Fill with cement.
  • Larger defects: Use particulate bone graft.
  • Big defects: Use metallic augments, allografts, or endoprostheses.
  • Uncontained defects: Likely require metallic augments.
  • Stem use: Stems help dissipate stress at the bone-implant interface, preventing rapid loosening.
    • Indicated for instability, protecting bone graft, and dubious metaphyseal fixation.

Levels of Constraint

  • Unconstrained CR or PS: Rare for TKR revision.
  • Semi-Constrained PS: Wider, taller post, effective for medio-lateral instability but risks post wear.
  • Fully Constrained Fixed or Rotating Hinge: Used for very unstable knees with no collateral competence.
    • Requires more bone resection.
    • Prevents hyperextension.

Implant Constraints

  • Increased constraint is counteracted by:
    • Rotating platform or rotating hinge.
    • Stemmed implants to dissipate stresses.
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