A Study to Assess the Changes in Bone Around Cementless Knee Replacements

The intervention being studied prospectively is an Oxford cementless unicompartmental knee replacement in subjects with osteoarthritis of the knee. A DXA scanner will be used to evaluate the change in bone mineral density (BMD) around these knee implants postoperatively over a 5 year period. 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. Bone loss around the knee prosthesis is an important factor in assessing long-term implant stability and survival. Post-transplantation bone loss is generally caused by a phenomenon known as stress shielding, or loss of bone density, which leads to less dense and weaker bones. Current practise post unicompartmental knee replacements is to follow up with a protocol of clinical evaluations including outcome scores and X-rays at regular intervals. However visual analysis of these radiographs provides no means of quantifying bone loss, and is unreliable with low precision of around 30% accuracy. In the past the only accurate method of assessing the bone in this area has been with a CT scan which exposes the subject to a significant dose of radiation. The uncemented Oxford unicompartmental knee replacement has been introduced in the last 5 years, with X-rays 2 years post-operatively showing good remodelling around the implant. Historically, uncemented unicompartmentatl knee replacements have poor survival results on international Joint registries. No studies on bone density/bone remodelling around unicompartmental knee replacements have been done, which is why we are proposing using iDXA, the latest bone density machine and software, in order to record bone quality around the implants. This bone density machine exposes the subject to approximately 1/10th of the radiation of a routine knee x-ray. Our hypothesis is that evaluating the bone quality beneath the tibial components will indicate whether the bone has bonded to the implant and also whether the observed x-ray changes are actually related to the functional outcomes. We believe that if the quality of the scan is good enough it may then supersede the normal x-ray as a method of evaluating the status of a knee replacement. Use of the iDXA orthopaedic knee application is investigational and has not yet been cleared for general use, so the measurement will be done under investigator supervision and IRB approval. 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 an iDXA scan throughout the study at the following timepoints: Up to 7 days pre operatively: Hip, spine and affected knee (the hip and spine are only scanned once pre operatively to identify if osteoporosis is present, and the knee is scanned as a baseline) Post operatively: Operated knee at 6 weeks, 6 months, 12 months, 18 months, 2 years and 5 years post operatively Standard clinical assessments will be performed during the study, and will include a radiograph of the operated knee, assessment of the participants Knee Society Score, and completion of the Total Knee Replacement questionnaire by the participant. The standard clinical assessments will take place up to 7 days pre operatively and at the 6 month, 12 month, 18 month, 2 year and 5 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 iDXA scan and other activities for the 5 years postoperative visit are performed.