Arthroplasty iSAWE 9

Question

A 63 year old woman has persistent medial knee pain a year after total knee arthroplasty.

Arthroplasty iSAWE 9, AP radiograph of a total knee arthroplasty
AP radiograph of a total knee arthroplasty. Image by Manjunath Ramappa and Andrew Port, Wikimedia Commons, CC BY 2.0.
  1. What does the radiograph show?
  2. How do you investigate the painful TKA?
  3. What causes of pain relate to component position?

Answer

Radiograph

  • Tibial component overhang medially (arrow)
  • Overhang over 3 mm increases the risk of pain
  • Irritates the MCL and pes anserinus

Investigation

  • Exclude infection first, CRP, ESR and aspiration
  • Exclude referred pain from the hip and spine
  • Long leg alignment films
  • CT for component rotation
  • Bone scan or SPECT CT for loosening
  • Diagnostic local anaesthetic injection for focal soft tissue pain

Component related causes

  • Internal rotation of the tibial or femoral component, causes patellar maltracking and pain
  • Overhang of the tibial or femoral component
  • Oversized femur overstuffs the patellofemoral joint
  • Instability (flexion, mid flexion or extension gap)
  • Aseptic loosening
  • Malalignment
  • Revision without a defined cause has poor results

Related pages

Author Contributions

Orthofracs team

Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 10 October 2026.