Progressive periacetabular osteolysis following total hip arthroplasty may require revision surgery. The purpose of this study was to use computed tomography scans of hemipelves retrieved at autopsy from patients who had had a total hip arthroplasty, to define the radiographic characteristics that differentiate clinically important osteolytic lesions from osteoarthritic bone cysts.

We analyzed forty-four hemipelves that had been retrieved at autopsy at a mean of eight years after a total hip arthroplasty with an uncemented acetabular component. Computed tomography images were analyzed to identify the location, volume, and presence of cortical erosion and/or communication pathways with the joint space for all periacetabular bone defects. Lesions that were not present on preoperative or immediate postoperative plain radiographs were defined as new lesions. These new lesions were compared with those that were present on preoperative or immediate postoperative plain radiographs, which were defined as preexisting lesions.

Forty-six lesions were identified on computed tomography, and sixteen of them were preexisting lesions. The mean volume of the preexisting lesions was 1.5 +/- 1.5 cm(3), which was significantly smaller than the mean volume of 5.6 +/- 11.4 cm(3) of the thirty new lesions (p = 0.034). Twenty-eight of the thirty new lesions had a clear communication pathway with the joint space, while thirteen of the sixteen preexisting lesions demonstrated no communication pathway. New lesions were significantly more likely to communicate with the joint space than were preexisting lesions (p < 0.001). Cortical erosion was seen in sixteen of the thirty new lesions; none of the sixteen preexisting lesions exhibited cortical erosion (p < 0.001).

The most important difference between osteolytic lesions and preexisting bone defects was the presence of a communication pathway to the joint space. Lesions that did not have an identifiable communication to the joint space were smaller and were not associated with cortical erosion. Lesions with communication to the joint through multiple pathways or through a central dome hole were larger and more likely to be associated with cortical erosion.