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Background: The development of three-dimensional computed tomography (CT) imaging techniques has enabled the detection, accurate measurement, and monitoring of periprosthetic osteolytic lesions. The aim of this study was to track the progression in size of osteolytic lesions and to determine those factors that are associated with the risk of progression. A secondary aim was to investigate whether progression in size of osteolytic lesions could be monitored with use of radiographs.Methods: We retrospectively determined, with use of sequential CT scans, the progression of periacetabular osteolysis over a period of as much as nine years in a cohort of twenty-six patients (thirty acetabular components) in whom the cementless acetabular component or components had been in place for longer than ten years at the time of the initial CT scan. High-resolution CT scans with metal-artifact suppression were used to determine the volume of osteolytic lesions. Progression in the size of osteolytic lesions per year was calculated as the change in the volume of osteolytic lesions between serial CT scans. Associations were determined between the progression in size of osteolytic lesions, osteolysis rate at the initial CT, patient age, sex, walking limitations, and activity level. Progression in size of osteolytic lesions as determined with use of CT was compared with that determined with use of radiographs.Results: Mean progression in the size of osteolytic lesions, as determined with use of CT, was 1.5 cm(3)/yr (range, 0 to 7.5 cm(3)/yr). The amount of osteolysis at the initial CT scan and patient activity were good predictors of osteolytic lesion progression. The strongest predictor of osteolytic lesion progression occurred when these two risk factors were combined (p = 0.0019). The value of radiographs was limited to monitoring of larger lesions identified by CT.Conclusions: This is the first study to report on the progression of osteolysis adjacent to cementless acetabular components from medium to long-term follow-up. The data suggest that the osteolysis rate at the initial CT and patient activity can be useful factors in predicting the progression in size of periacetabular osteolytic lesions. [ABSTRACT FROM AUTHOR]