Proximal tibial bone mineral density (BMD) has been shown to decrease following Total Knee Arthroplasty (TKA) by both dual-energy x-ray absorbtiometry (DEXA) and quantitative computed tomography (qCT)-assisted osteodensitometry. Little is known about changes in BMD following unicompartmental knee arthroplasty (UKA). Additionally, there are proposed differences in stress transmission between cemented metal and polyethylene (PE) components. We proposed two hypotheses. First, that proximal tibial BMD decreases following UKA. Second, that BMD loss would be greater below metal tibial components. We performed a prospective clinical trial of 50 consecutive UKAs in 49 patients performed by two surgeons at one institution. There were 25 mobile bearing Oxford and 25 fixed bearing Accuris arthroplasties, all were medial. BMD was assessed with qCT-assisted osteodensitometry scans prior to discharge and then at 1 and 2 years post surgery. Each CT slice was divided into medial and lateral halves and cortical and cancellous bone was analysed separately. The six 2mm slices immediately beneath the tibial implant were analysed using previously validated software to create a three-dimensional assessment of BMD. The lateral half was used as a control. There were a total of 30 females (60%), with an average age of 70 (49–84). One patient was lost to follow-up and another was unable to be analysed due to failure requiring revision before follow-up was complete. Preliminary results showed no significant change in BMD at either 1 or 2 years follow-up. There was no difference in BMD change between the mobile and fixed bearing prostheses, between the medial and lateral halves nor between cortical and cancellous bone. Final results will be presented at the AONZOA conference. This trial shows that UKA does not result in significant change to BMD at 2 years. The preservation of BMD may indicate that UKA is better at maintaining physiologic stress transfer than a TKA, which has been shown to be associated with a reduction in BMD.
Lumbar Total Disc Replacement (LTDR) is an alternative to fusion for the surgical management of discogenic back pain not responding to conservative therapy. Theoretical advantages include preservation of motion and possible reduction in adjacent segment degeneration. The aim is to review the early results of LTDR in an Auckland private practice. A prospective study was carried out on 32 consecutive patients treated with LTDR. Discogenic back pain was confirmed with plain radiographs, MRI and CT lumbar discogram. The Charité TDR was used in 19 patients and A-MAV in 13. Follow-up was to a minimum of two years. Patients completed Modified Roland Questionnaires (MRQ), Visual Analogue Pain Scores (VAPS) and Lower Back Outcome Scores (LBOS) pre and post-operatively. Patients’ notes and radiographs were reviewed. All outcomes measures improved significantly. Mean MRQ scores improved from 14.2 to 6.4 and 4.8 (at one and two years respectively). Mean VAPS improved from 5.3 to 2.5 and 1.7. Mean LBOS improved from 33 to 52 and 57. 84% had radiographic evidence of motion at the level of the prosthesis. There were four major complications. A retroperitoneal haematoma, an incisional hernia, a ureteric stenosis and subsidence of the prosthesis each occurred in separate patients. These all occurred in the first ten patients of the study and were related to the approach. There were no major thrombo-embolic or infective complications and no revision surgery was required. LTDR is a safe and effective surgical treatment of discogenic back pain. There is however, a steep learning curve with regard to the approach and a higher risk of complications during this time. Initial results are encouraging, but longer term follow-up needs to be performed.
