Updated: 6/11/2021

TKA Aseptic Loosening

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  • summary
    • TKA Aseptic Loosening is a macrophage-induced inflammatory response that results in bone loss and implant loosening in the absence of an infection.
    • Diagnosis can be made with plain radiographs of the knee.
    • Treatment is generally revision arthroplasty with exchange of all loose components.
  • Etiology
    • Steps in the process include
      • particulate debris formation
      • macrophage activated osteolysis
      • prosthesis micromotion
      • particulate debris dissemination
    • Pathophysiology
      • factors affecting wear rate of polyethylene in TKA
        • sterilization method
        • manufacturing method (conventional vs. crosslinked)
        • presence of third-body debris
        • motion between modular tibial insert and metal tray (i.e., backside wear)
        • roughness of femoral component counterface
        • alignment and stability of the TKA
          • malalignment causes asymmetric loading causes early loosening
          • more frequent with varus rather than valgus malalignment
        • demand or activity level of patient
  • Presentation
    • Symptoms
      • painless
        • early disease
      • pain
        • location
          • localized to the tissues around the loose components
        • aggrevating factors
          • weightbearing
          • often activity related
    • Physical exam
      • may have minimal pain with ROM
      • increased pain with weight bearing
    • Radiographs
      • recommended views
        • AP
          • tibial osteolysis readily visible on AP
          • femoral osteolysis may be difficult to detect on AP as lesions are typically located in posterior condyles and are obscured by the femoral component
        • lateral
        • oblique
          • often more helpful for identifying femoral osteolysis
      • findings
        • radiolucent area around implant or cement with sclerotic border
          • especially radiolucencies > 2 mm
        • change in position of the implant
          • varus or valgus subsidence of tibial component
        • progressive widening of cement-bone or bone-prosthesis interface
        • cement cracking or fragmentation
    • CT Scan & MRI
      • viable options for assessing larger osteolytic lesions to aid in preoperative planning
  • Studies
    • Serum labs
      • ESR normal
      • CRP normal
  • Differential
    • Critical to rule out periprosthetic joint infection 
  • Treatment
    • Nonoperative
      • observation
        • indications
          • stable implant with minimal symptoms
    • Operative
      • revision TKA
        • indications
          • pain due to aseptic loosening
          • pain with evidence of osteolysis
          • extensive osteolysis that would compromise revision surgery in the future
        • technique
          • bone graft
            • indicated for defects > 10 mm
            • often used in younger patients to preserve bone stock
          • prosthetic metal wedges/augments
            • indicated for defects > 10 mm
            • often used in elderly, low activity patients
          • bone cement
            • indicated for smaller defects
            • heat released can cause thermal necrosis of surrounding bone and vascular tissue which can potential lead to aseptic loosening
  • Techniques
    • Revision TKA
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(SAE08OS.31) A 67-year-old man who underwent knee arthroplasty 7 years ago now reports the recent onset of pain and swelling. He denies any recent illness or change in medical status. Examination of the knee reveals a moderate effusion, slight warmth when compared to the contralateral knee, and no tenderness. Pain is increased with weight bearing. Laboratory studies show a WBC count of 6,300/mm3 (normal 3,500-10,500/mm3), a hemoglobin level of 10.1 g/dL, an erythrocyte sedimentation rate of 25 mm/h (normal up to 20 mm/h), C-reactive protein (CRP) level of 0.3 mg/dL (normal less than 0.5 mg/dL), and a uric acid level of 6.2 mg/dL (normal 2.5-7.0 mg/dL). Postoperative and current radiographs are shown in Figures 8a and 8b. What is the most likely diagnosis?

QID: 6393
FIGURES:
1

Infection

6%

(25/451)

2

Aseptic loosening

27%

(120/451)

3

Osteolysis

60%

(272/451)

4

Dislodgement of polyethylene

4%

(18/451)

5

Crystalline arthropathy

2%

(11/451)

L 2 E

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