Revision TKR

Causes of failure

1. Infection
2. Instability
3. Failure of ingrowth in cemented components
4. Patella problems
5. Wear
6. Loosening

Deterioration of tibial baseplate locking mechanisms

• The stability of polyethylene liners on their tibial trays decreases with time
• micromotion occurs which can generate wear particles from the undersurface of the liner as well as the intended joint surface
• this is an example of Mode 2 wear, between one intended bearing surface and one unintended bearing surface

Insufficient plastic

• The plastic thickness should be at least 8mm.  

Malalignment

• Varus malalignment of the tibia of more than 5 degrees leads to premature tibial component loosening and failure.

Principles of treatment

• Establish a specific diagnosis.  Some of the modes of failure include:
  1. Progression of arthritis in a unicompartmental replacement
  2. Aseptic loosening
  3. Sepsis
  4. Instability
  5. Malrotation, poor patellar tracking
  6. Extensor rupture
  7. Stiffness
  8. Breakage
  9. Periprosthetic fracture
  10. Undiagnosed pain

History

• Pain profile
  • was the arthroplasty was painful from the start or became so?
    1. Same pain persists
       • Consider referred pain from hip or spine
       • Pre-existing sepsis
       • Over-stuffed arthroplasty
       • Failed bone ingrowth
       • RSD
    2. New and different pain
       • Rule out infection
       • Overstuffing
       • Malrotation
       • Failed bone ingrowth
       • RSD
    3. Different pain with stiffness
       • Overstuffing
       • RSD
    4. Initial pain relief
       • Aseptic loosening
       • Implant breakage
       • Infection (particularly if present at rest)
• Instabilty
  • Anatomic causes of giving way:
    1. Extensor mechanism pain
    2. Quadriceps weakness
    3. Quadriceps tendon rupture
    4. Patella fracture
    5. Patella subluxation/dislocation
    6. Patella tendon rupture
    7. Effusion
    8. Flexion contracture

Examination

General

1. Examine the spine and hip as possible sites for referred pain
2. Check inguinal nodes for regional lymphadenopathy
3. Check dentition, feet, sinuses as sources of sepsis
4. Examine gait

Knee

• integrity of the collaterals
• extensor mechanism
• Look
  • scarring, synovitis, effusion, oedema
• Feel
  • hypersensitivity of RSD,
  • increased warmth,
  • specific areas of tenderness,
  • pulses.
• Move
  • Quantify active and passive ROM. 
  • Extensor lag
    • Causes
      • quadriceps weakness,
      • pain inhibition
      • due to mechanical problems with the extensor mechanism.
  • Instability. 
    • Dislocation occurring in the AP plane
      • occurs most commonly with the knee in flexion
      • assessed with anterior and posterior drawer and posterior sag signs.
    • Varus/valgus stability
      • crucial;
      • if there is no functioning MCL a constrained implant will be necessary.
• Special Tests

Investigations

Joint aspiration

• Aspiration of more than 25 000 leukocytes/mL indicates sepsis. 
• Preoperative aspiration to be 75% sensitive and highly specific (96%) for detecting infection.

Radiology

• Long leg weight bearing films
• weight bearing AP and latera
• lateral in full flexion.
• Tips
  • If it seems impossible to get true AP films this implies mal-rotation of one of the components. 
  • Loosening
    • implied by a complete radiolucent line of 2mm or more around the prosthesis at the bone cement interface. 
    • Incomplete radiolucencies of <2mm are common and haven’t been shown to be correlated with poor clinical outcomes in cemented TKR

CT scans

• CT scanning can be used to assess for malrotation of the components.

Nuclear medicine

• Technetium bone scans are highly sensitive but unspecific for assessing painful TKRs.
• Increased uptake is present for a year after uncemented components are inserted.

Indications for revision

1. Infected prostheses
2. Loose prostheses
3. Stiffness with obvious mechanical impediment to motion
4. Patella tracking problems

• blind exploration of a painful TKR without a preoperative diagnosis lead to good outcomes in only 4%.

Treatment of infection

• Present gold standard is two stage re-implantation with antibiotic laden cement spacers, including a spacer in the supra-patellar pouch to preserve the tissue planes.

Treatment of instability

• AP instability
  • usually is due to posterior dislocation due to failure to balance the flexion and extension gaps. 
  • The knee usually needs to be made tighter in flexion, through insertion of a larger femoral component.
  • If there is persistent instability after the flexion gap has been adequately balanced a rotating hinged knee prosthesis will be necessary. 
• Valgus varus instability
  • is most commonly valgus instability due to stretching or incompetence of the MCL. 
  • This may need to be addressed by constrained prostheses or ligament reconstruction using allograft. 
  • Patients with an attenuated MCL can use a constrained condylar prosthesis. 
  • If the MCL is completely incompetent a rotating hinge constrained knee is required, however it is rare that a rotating hinged prosthesis will be necessary for varus valgus instability alone.
  • Options for treatment of the medial collateral ligament
    • tibial advancement,
    • proximal femoral advancement with a bone plug,
    • imbrication of the midportion of the ligament.

Treatment of malrotation

• Usually due to excessive femoral internal rotation, which results in patellar mal-tracking.

Treatment of extensor tendon rupture

• Workup
  • establish what caused the rupture
    • e.g. oversized femoral component, malrotation, excessively thick patella.
• Options
  • Primary repair
    • is not effective.
  • Tendon transfer
    • Semitendinosis transfer is effective
  • Allograft
    • extensor tendon allografts may also be used. 
      • They will need to be protected with cerclage wires through the patella.

Treatment of massive bone loss

• Options
  • structural allograft. 
    • If an allograft is used the prosthesis is usually cemented into it, and the allograft is attached to the remaining bone with a step cut and cables.
  • tumour prosthesis

Surgical steps

1. Incision
   • Use most lateral scar
   • Cross transverse scars at a right angle
   • Consider plastic surgery input
   • Can use staged incisions or soft tissue expanders
2. Exposure
   • Quadriceps snip
   • V-Y quadriceps plasty. 
     • Need to protect against active extension for 6 weeks if this is done. 
     • Long term strength can return to near normal (Windsor and Insall)
   • Tibial tubercle osteotomy. 
     • Excellent choice if need to elevate patella or if a long stemmed tibial component needs to be explanted. 
     • If a tibial tubercle osteotomy is to be used a stem that extends past the osteotomy site is necessary.
   • Femoral peel. 
     • All the soft tissues are peeled off the distal femur, including the collateral ligaments. 
     • When these are replaced at the end of the procedure there is often adequate stability without added constraint.
3. Implant removal
4. Frozen section
5. Reestablish height of joint line (height of tibial articular surface)
   • use fibular heights and meniscal scar. 
   • The joint line is generally 1.5-2cm a above the fibular head.
6. Address bony defects
   • Constrained
     • bone graft or if less than 1cm can cement
   • Unconstrained
     • augments
7. Stability and balancing of flexion and extension gaps.
8. Assessment of patella tracking.

Use of stems

• Action
  • act as a load sharing device. 
• Indication
  • significant loss of metaphyseal support. 
  • if augments have been required.
  • in constrained designs to dissipate the increased forces on the prosthesis
  • to extend past the site of a tibial tubercle osteotomy.

Results

• The infection rate is higher
  • 5.6%
  • If a reoperation is required after revision, the infection rate is higher still, at around 20%.
• 22% reoperation rate at 10 years