ASEPTIC LOOSENING OF THR

ASEPTIC LOOSENING OF THR

• loosening most serious complication of THR – most common cause of revision
  • septic – d/t infection
  • aseptic – d/t osteolysis

Osteolysis

• generation of wear particles – access of wear particles to periprosthetic bone – cellular response to particulate debris
• main source of particulate debris is polyethylene liner
• all periprosthetic area accessible to joint fluid (effective joint space) are vulnerable
• effective joint reduced by
  • porous coating of proximal stem
  • fewer screw holes in acetabular component

Clinical features

• may be asymptomatic
• groin pain more during initial weight bearing (start up pain)
• pain alleviated by rest – aggravated by rotation of hip

Radiographic features

• Cemented components
  • Femoral stem
    • definitive loosening
      • migration of the component
      • # or fragmentation of cement
      • # or deformation of the component
      • radiolucency at cement bone interference
    • probable loosening
      • radiolucency at cement bone interference at periphery of component >50% of circumference – at least in one radiograph
    • possible loosening
      • <50% stem circumference and less than 100% periphery of the component
  • acetabular components
    • radiolucency >2mm wide surrounding the entire component
    • migration of cup : change in version and horizontal inclination
• Uncemented components
  • radiographic signs of bone ingrowth and stable fixation
    • spot welding at distal porous coated surface
    • stress shielding of medial cortex
    • absence of radiolucent or reactive lines on lateral cortex
  • stable fibrous fixation
    • absent spot welds
    • lack of stress shielding of medial cortex
    • radiolucent line around the circumference of the component - <1mm wide
    • reactive bone formation parallel to stem
    • slight calcar hypertrophy
  • unstable fibrous fixation
    • calcar hypertrophy
    • solid distal
    • subsidence or migration of component
    • reactive zone around the stem that is divergent

Technical problems contributing to stem loosening

• failure to remove soft cancellous bone while preparing prosthesis bed
• failure to remove all trabecular bone from the canal
• inadequate quantity of cement
• inadequate pressurization of cement
• failure to centralize the stem
• presence of voids in the cement
• failure to keep the bolus of cement intact to avoid lamination
• failure to prevent stem motion while cement is hardening

Treatment

• aseptic loosening is a radiographic diagnosis
• does not constitute an indication of surgery
• loose symptomatic components can be revised if patient can tolerate another surgery
• asymptomatic cases : surgery in progressive osteolysis
  • so close follow up in such cases
  • early stages of osteolysis : lesion bone grafted along with exchange of acetabular liner and femoral head

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