Updated: 9/6/2018

TKA Aseptic Loosening

Topic
Review Topic
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Questions
1
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Evidence
1
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https://upload.orthobullets.com/topic/12754/images/apos.jpg
https://upload.orthobullets.com/topic/12754/images/latos.jpg
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https://upload.orthobullets.com/topic/12754/images/intraop.jpg
Introduction
  • Macrophage-induced inflammatory response resulting in bone loss
    • steps in the process include    
      • particulate debris formation
      • macrophage activated osteolysis 
      • prosthesis micromotion
      • particulate debris dissemination
    • see wear and osteolysis basic science for full description 
  • 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
Imaging
  • 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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Questions (1)

(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? Review Topic

QID: 6393
FIGURES:
1

Infection

1%

(1/74)

2

Aseptic loosening

23%

(17/74)

3

Osteolysis

65%

(48/74)

4

Dislodgement of polyethylene

5%

(4/74)

5

Crystalline arthropathy

1%

(1/74)

ML 2

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PREFERRED RESPONSE 3
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