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arthroplasty

Painful Total Knee Arthroplasty

advanced
6 min
20 marks
6 questions
Clinical Scenario
A 65-year-old man presents with persistent anterior knee pain 18 months after primary TKA for osteoarthritis. He describes diffuse pain, worse with stairs and kneeling. He had been progressing well until 6 months ago when symptoms began. The knee has "never felt right." On examination, he walks with a limp. Range of motion is 5-95 degrees. Ligaments are stable. There is tenderness over the medial joint line and pes anserinus area.
AP, lateral, and skyline radiographs of TKA showing well-positioned components with neutral alignment. No obvious loosening, radiolucent lines, or malalignment. Joint line appears appropriate. Patella tracks centrally on skyline.
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AP, lateral, and skyline radiographs of TKA showing well-positioned components with neutral alignment. No obvious loosening, radiolucent lines, or malalignment. Joint line appears appropriate. Patella tracks centrally on skyline.

Source: Educational radiographic series of a total knee arthroplasty • OrthoVellum Medical Education Team • OrthoVellum Educational Use

Questions

Question 1 (4 marks)

What is your differential diagnosis for painful TKA?

Question 2 (4 marks)

What investigations would you perform? Include specific thresholds.

Question 3 (3 marks)

CRP is 12 mg/L. Aspiration shows WCC 1500/μL with 45% PMN, cultures negative. How do you interpret these results?

Question 4 (4 marks)

CT shows 8° internal rotation of the femoral component. What is the significance and management options?

Question 5 (3 marks)

What technical factors during primary TKA help prevent anterior knee pain?

Question 6 (2 marks)

What are the outcomes of revision TKA for unexplained pain?

Exam Day Cheat Sheet

Must Mention

  • •EXCLUDE INFECTION FIRST (aspiration, CRP, alpha-defensin)
  • •CT rotation protocol: femoral IR >3° = significant
  • •Combined rotation (femoral + tibial) >10° = problematic
  • •Revision for unexplained pain = 40-50% satisfaction ONLY
  • •Always examine hip and spine for referred pain
  • •Cannot fix rotation with poly exchange - need component revision

Common Pitfalls

  • •Revising without clear mechanical cause
  • •Missing component malrotation on plain films
  • •Not examining hip/spine
  • •Poly exchange for rotational malposition (won't work)
  • •Not considering pes anserinus/soft tissue causes