What is the recommended treatment approach for a patient requiring a patella implant?

Patella Implant Treatment Approach

For patients requiring a patella implant, surgical intervention with a porous tantalum implant is recommended as the primary treatment approach, particularly for cases with severe patellar bone loss during revision total knee arthroplasty. 1

Diagnostic Evaluation

• Radiographic Assessment:

  • Standard radiographs (anteroposterior, lateral, and axial views) are the first-line imaging modality for evaluating patellar complications 2
  • Weight-bearing axial radiographs are particularly valuable for assessing patellofemoral kinematics 2

• Advanced Imaging:

  • CT scan with metal artifact reduction techniques is the preferred modality for measuring axial malrotation of knee prosthesis components 2
  • CT scanning is superior for evaluating patellar alignment and can help predict outcomes after surgical intervention 3

Indications for Patella Implant

• Severe patellar bone loss during revision total knee arthroplasty
• Failed previous patellar component
• Patellar component loosening or wear
• Patellar fractures with significant comminution that cannot be reconstructed
• Patellofemoral instability with structural defects

Surgical Considerations

• Component Selection:

  • Porous tantalum implants show excellent results for revision and salvage patellar arthroplasty with substantial improvement in function and pain reduction 1
  • Metal-polyethylene components have historically shown higher failure rates compared to newer materials 2

• Technical Factors:

  • Proper rotational alignment of femoral and tibial components is critical to prevent patellofemoral complications 2
  • Excessive combined internal rotation of tibial and femoral components is directly proportional to the severity of patellofemoral complications 2

Post-Surgical Management

• Rehabilitation Protocol:

  • Land-based exercise (both cardiovascular and resistance) is strongly recommended 2
  • Aquatic exercise can be beneficial, especially for deconditioned patients 2
  • Weight loss is strongly recommended for overweight patients 2

• Pain Management:

  • Acetaminophen (up to 4,000 mg/day) with appropriate counseling to avoid other acetaminophen-containing products 2
  • Oral or topical NSAIDs if acetaminophen is insufficient 2
  • Intraarticular corticosteroid injections for persistent pain 2

• Supportive Measures:

  • Medially directed patellar taping is conditionally recommended 2
  • Appropriate wedged insoles based on compartment involvement 2
  • Thermal agents and walking aids as needed 2

Complications to Monitor

1. Mechanical Issues:

   • Subluxation or dislocation (occurs in 1-12% of cases) 2
   • Component loosening or wear 2
   • Impingement 2

2. Structural Problems:

   • Patellar fractures (occur in up to 5.2% of patients, usually within first few postoperative years) 2
   • Osteonecrosis 2

3. Functional Limitations:

   • Patellofemoral instability (often due to internal malrotation of components) 2
   • Reduced range of motion
   • Persistent pain

Follow-up Protocol

• Regular radiographic assessment to monitor implant position and integration
• Evaluation of pain, function, and range of motion
• Assessment for complications such as component loosening or wear

Clinical Outcomes

Patients with porous tantalum implants for revision patellar arthroplasty have shown significant improvements:

• Average knee function scores improved from 24 to 69
• Average pain scores improved from 20 to 53
• Average range of motion increased from 62° to 103° 1

Pitfalls and Caveats

• Failure to properly assess patellar alignment with CT scanning may lead to poor surgical outcomes 3
• Metal-on-metal contact can occur with patellar component failure and may lead to global joint failure 2
• Patellar remodeling can occur in non-resurfaced patellae, potentially resulting in anterior knee pain or fracture 2