summary THA 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 hip. Treatment is generally revision arthroplasty with exchange of all loose components. Etiology Steps in the process prosthesis micromotion particulate debris formation macrophage activated osteolysis See wear and osteolysis basic science for full description Presentation Symptoms pain location groin pain thigh pain knee pain aggrevating factors often activity related Physical exam may have minimal pain with ROM increased pain with weight bearing Radiographs recommended views AP lateral findings (xrays are not sensitive for osteolysis and typically underestimate extent of involvement) lucency > 2 mm at cement-bone or metal-bone interface component motion with stress views femoral component subsidence > 1 cm fracture of cement mantle change in peg-neck angle can also represent femoral head necrosis/collapse, femoral neck fracture decreased distance from tip of peg to lateral femoral cortex can also represent femoral head necrosis/collapse narrowing of femoral neck after 3 years or > 10% can also represent impingement acetabular component migration or change in position/inclination wearing of polyethylene liner leads to asymmetric superior location of femoral head within acetabular cup Studies Serum labs ESR will be normal CRP will be normal Treatment Nonoperative observation indications stable implant with minimal symptoms Operative revision THA Indications pain due to aseptic loosening pain with evidence of osteolysis extensive osteolysis that would compromise revision surgery in the future.