A Study to Assess Bone Density and Quality Around the Uncemented Acetabular Socket of a Hip Replacement Pre operatively and over 2 years Following Surgery

The intervention being studied prospectively is an uncemented total hip arthroplasty in subjects with hip osteoarthritis. A DXA scanner will be used to evaluate the change in bone mineral density (BMD) around 3 types of uncemented acetabular components used in total hip arthroplasty. The 3 types of acetabular components are as follows, in order of increasing stiffness: 1) The RM Pressfit cup (Mathys) - a monoblock implant made of ultra high molecular weight polyethylene coated with titanium particles. It has a modulus of elasticity very similar to bone. 2) The Trabecular Metal Modular Acetabular cup (Zimmer) - consists of a shell made from Trabecular Metal and can accept a variety of liners. It resembles bone and has a porous structure, facilitating rapid bony ingrowth. 3) The Pinnacle Acetabular Cup (DePuy) - a 180 degree titanium shell, designed to accept a variety of liners. A DXA scanner is a diagnostic machine that measures bone density and body composition. DXA stands for dual-energy x-ray absorptiometry, and is a well-validated and widely used technique that provides an accurate and precise quantitative assessment of BMD. The rationale behind using a DXA scanner pre and post operatively in this study is as follows. Of all hip arthroplasties performed worldwide each year, a small but significant rate of failure persists in the form of aseptic loosening, predominantly of the acetabular component. There is also the known phenomenon of stress sheilding, or loss of bone density, around uncemented acetabular components, although the long-term effects of this remain unclear. This loss of BMD around orthopaedic implants only becomes apparent on X-ray when significant (about 70%) bone density is lost. Periprosthetic bone loss is an important factor in assessing long-term implant stability and survival. DXA is a proven method of detecting bone loss before it becomes apparent on X-ray. Additionally, recent studies using 3D quantitative computed tomography (qCT) technology have demonstrated periacetabular BMD loss but exposes the subject to a significant radiation dose of 2.5-3.0 milliSiverts (mSv), whereas DXA exposes the subject to approximately 0.009mSv, which is around 1/30th of the radiation of a routine hip X-ray. The hypothesis is that using the DXA scanner to evaluate the bone quality around the acetabular component will indicate whether osteo-integration has occurred before changes are observed on X-ray changes or are demonstrated clinically, and thus may even supercede the the normal X-ray as a method of evaluating the status of a hip replacement. The staff performing the DXA scan come from a Registered Nurse background, have completed the Australia, New Zealand Bone Mineral Society (ANZBMS) Clinical Bone Densitometry Training Course, and each have a minimum of 4 years experience in using the DXA BMD scanner. Before the participants enter the study they will be provided with a Participant Information Sheet and Consent Form that explains what their participation in the study will involve including study procedures, potential risks and benefits, who is responsible for costs, compensation for injury during the study, and how the study information will be stored and used. The participants will undergo a DXA scan throughout the study at the following timepoints: Pre operatively: Both hips, and spine (contralateral hip and spine are only scanned this once to identify and exclude those with pre-existing osteoarthritis). Post operatively: Operated hip at 6 weeks, 6 months, 1 year and 2 years post operatively. At the 6 week visit, an additional 2 DXA scans will be performed in order to determine the precision of the DXA scan. Standard clinical assessments will be performed during the study, and will include a radiograph of the operated hip, and completion of the following questionnaires: Oxford hip, HAAS, WOMAC, and the UCLA activity scale (see secondary outcomes for acronym explanations). These will all take place pre operatively and at the 6 month, 12 month, 1 year and 2 year timepoints (ie. this excludes the 6 week timepoint). Participants will have individualised appointment dates for the above activities, which will be performed at the local hospital where both the DXA scanner and X-ray departments are located. The participant will be routinely assessed by the surgeon in their rooms located in the same hospital. Once the DXA technician has completed the scan, they will have the participant complete the questionnaires, and report any changes in medications and any adverse events that have occurred since their last visit. Each of these visits should take 20-30 minutes to complete plus the extra time needed for the routine X-ray and surgeon followup assessment. Each participants involvement in the study will end once the final DXA scan has been completed at the two year timepoint.