Although total hip replacement (THR) is amongst the most successful and beneficial medical procedures to date, long-term outcomes continue to suffer from aseptic loosening secondary to peri-prosthetic osteolysis. Extensive research over the last two decades has elucidated a central mechanism for osteolysis in which wear debris generated from the implant stimulates inflammatory cells to promote osteoclastogenesis and bone resorption. The cytokine tumor necrosis factor alpha (TNFalpha) has been demonstrated to be central to this process and is considered to be a leading target for intervention. Unfortunately, even though FDA approved TNF antagonists are available (etanercept), currently there are no reliable outcome measures that can be used to evaluate the efficacy of a drug to prevent peri-prosthetic osteolysis. To the end of developing an effective outcome measure, we evaluated the progression of lesion size in 20 patients with established peri-acetabular osteolysis (mean=29.99 cm(3), range=2.9-92.7 cm(3)) of an uncemented primary THR over 1-year, using a novel volumetric computer tomography (3D-CT) technique. We also evaluated polyethylene wear, urine N-telopeptides and functional assessments (WOMAC, SF-36 and Harris Hip Score) for comparison. At the time of entry into the study baseline CT scans were obtained and the patients were randomized to etanercept (25 mg s.q., twice/week) and placebo in a double-blinded fashion. CT scans, urine and functional assessments were also obtained at 6 and 12 months. No serious adverse drug related events were reported, but one patient had to have revision surgery before completion of the study due to aseptic loosening. No remarkable differences between the groups were observed. However, the study was not powered to see significant drug effects. 3D-CT data from the 19 patients was used to determine the mean increase in lesion size over 48 weeks, which was 3.19 cm(3) (p<0.0013). Analysis of the urine N-telopeptides and functional assessment data failed to identify a significant correlation with wear or osteolysis. In conclusion, volumetric CT was able to measure progression of osteolysis over the course of a year, thus providing a technology that could be used in therapeutic trials. Using the data from this pilot we provide a model power calculation for such a trial.