Total Hip Arthroplasty: Aseptic Loosening

Despite the success of total hip arthroplasty (THA), aseptic loosening is still one of the most common complications. While cemented THAs are fixed using cement, cementless ones achieve fixation by bony ingrowth, called osseointegration. Aseptic loosening refers to the failure of joint prostheses without the presence of other mechanical causes or infections. In the current chapter, our objective was to discuss pathophysiology, diagnosis, risk factors, preventive measures, and management of aseptic loosening after THA. It is a complex and likely multifactorial event that is generally described as a macrophage-induced inflammatory response that results in bone loss and implant loosening in the absence of an infection. This complication is diagnosed based on clinical and radiographic evaluation. Clinical symptoms suggestive of aseptic loosening include pain on weight-bearing, which may be present in the thigh or groin. There is no standard manner of radiographic assessment when suspecting the loosening of the implant. The single most important rule in the evaluation of radiographs is “>2 mm rule.” This rule states that if osteolysis, radiolucent lines, cup migration, or stem subsidence exceeds 2 mm within time frame of 2 years after primary THA, there is likely need for revision surgery in almost half of the cases. Patient-related risk factors are as follows: proximal femoral bone geometry, large non-tapering femoral canal shape (stove pipe), posttraumatic arthritis and osteonecrosis, developmental dysplasia of the hip, age <65 years, increased activity level, particularly high-impact and competitive sports, and male gender. Surgical risk factors mostly described for cemented THAs are as follows: cement mantle with inadequate thickness, lesser cement intrusion due to removal of all trabecular bone or inadequate cement pressurization, undersized components, femoral and cup malpositioning, etc. Preventive strategies include the advent of ultramolecular weight polyethylene and modern cementless implant design ensuring proper biologic fixation. Appropriate sizing and positioning of the components are also paramount. The management of aseptic loosening depends on the degree of bone loss around femoral and acetabular components. Depending on the bone stock in femoral metaphysis or diaphysis, only proximal to fully coated stems to fluted tapered stems, and in severe cases, megaprosthesis or impaction grafting techniques might be indicated. Similarly, while in the setting of minor bone loss in acetabulum, a standard acetabular component can be used, when the acetabular rim is not supportive, acetabular augments, jumbo cups, or cup-cage implants may be necessary.