Can the volume of pelvic osteolysis be calculated without using computed tomography?

UNLABELLED: The most common method to diagnose and monitor osteolysis is the standard anteroposterior radiograph. Unfortunately, plain radiographs underestimate the incidence and extent of osteolysis. CT scans are more sensitive and accurate but also more expensive and subject patients to more radiation. To determine whether the volume of pelvic osteolysis could be accurately estimated without a CT scan, we evaluated the relationships between CT volume measurements and other variables that may be related to the size of pelvic osteolytic lesions in 78 THAs. Only the area of pelvic osteolysis measured on radiographs, heavy patient activity level, and total volume of wear were associated with the pelvic osteolysis volume measured on CT in the context of the multivariate regression analysis. Despite a strong correlation (r = 0.93, r(2) = 0.87) between these three variables and the volume of pelvic osteolysis measured on CT, estimates of pelvic osteolysis volume deviated from the actual volume measured on CT by more than 10 cm(3) among eight of the 78 THAs in this study. CT images remain our preferred modality when accurate assessments of pelvic osteolysis volume are required. LEVEL OF EVIDENCE: Level III, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence.