Review Question - QID 210222

Osteolysis is caused by particulate debris activation of macrophages with subsequent bone resorption seen as expansile lytic lesions on radiographs.

Supra-acetabular osteolysis can occur secondary to particular debris most commonly generated from ultra-high molecular weight polyethyelne (UHMWPE) debris. Prior to the development of highly cross-linked polyethylene liners eccentric wear or backside wear of polyethylene liners lead to the production of high volumes of polyethylene particle debris. Particulate debris led to macrophage activation and the production of osteolytic lesions behind acetabular cups or around acetabular screws. This process often occurs more than 10 years out from the index surgery and can go on to cause fracture or loosening of components due to loss of prior bone ingrowth. Osteolysis rates have significantly decreased since the introduction of highly cross-linked polyethylene liners which have much lower wear rates.

Clohisy et al. in 2004 retrospectively reviewed 439 patients to investigate the reason for revision hip surgery. They found 55% of revisions were for aseptic loosening, 14% for instability, and 13% for osteolysis around a well-fixed implant. They concluded aseptic loosening was the most common reason for revisions surgery and osteolysis around a well-fixed component was a common reason for late revisions. (Of note this study was performed in 2004, reviewing outcomes of the older generation UHMWPE.)

Schmalzried et al. review wear in total hip and knee arthroplasty. They state osteolysis around uncemented acetabular components tends to migrate away from the implant interface into the cancellous bone of the pelvis. These expansile lytic lesions may be asymptomatic until pelvis fracture occurs. If noted, they recommend at least annual radiographic examination to monitor the progression of osteolysis.

Figures A and B show an AP and iliac oblique view, respectively, of supra-acetabular osteolysis characterized by a lytic lesion behind the acetabular cup and eccentric wear of the polyethylene liner.

Incorrect Answers:
Answer 1: Metal-on-metal implants can lead to an aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL) with surrounding soft tissue damage or pseudotumor.
Answer 3: Trunnionsis or wear of the femoral head-neck interface can lead to failure of total hip arthroplasty due to metal ion related complications or due to gross trunnion failure.
Answer 4: Osteoporosis is characterized by a global age-related bone mass secondary to an imbalance between osteoblast and osteoclast activity.
Answer 5: Stress shielding can be seen when implants alter the typical forces seen by bone leading to local loss of bone density.