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.