The postoperative radiological evaluation of the Oxford Microplasty® unicompartmental knee replacement instrumentation
Introduction. Recently, new model of Oxford mobile-bearing unicompartmental knee arthroplasty (UKA, Oxford Microplasty®, Zimmer Biomet, IN, USA) was launched to improve previous version (Oxford Phase 3, Biomet, IN, USA). Still, there are few reports demonstrating the results of this noble UKA prosthesis in the literature. Thus, the aim of this study is to report and assess the postoperative radiological outcomes of the Oxford Microplasty <sup>®</sup> instrument. Materials and methods. From March 2013 to October 2013, twenty-one patients (23 knees) underwent mobile UKA for medial compartment osteoarthritis using this noble instrument. Postoperative radiological outcomes were measured for operated lower limb alignment and implant position, and they were compared with those of 64 UKAs using the Oxford Phase 3 which had been performed from January 2010 to August 2012. Pre-and post-operative deformity of the knee in the coronal plane, the location of the mechanical axis with respect to the center of the tibial surface, positioning of the tibial and femoral components and varus and valgus alignment for the tibial and femoral components were evaluated. Results. In the Microplasty® patients, preoperative HKA angle was 172.8±2.5° and postoperative HKA angle increased to 177.7±2.8° (p<0.001). There were no significant differences in postoperative HKA angle between Oxford Phase 3 and Microplasty group (178.4° vs. 177.7°, p>0.05). There were no significant differences in postoperative limb alignment and component position between the Microplasty group and Oxford Phase 3 group except femoral component flexion (11.9±2.1° vs. 2.6±4.1°, p<0.001). In addition, there were not any outliers in measurements of the components in the Microplasty group. Conclusion. UKA using Oxford Microplasty® includes noble tools including femoral sizing spoon, G-clamp, longer IM rod, two-peg femoral component, and IM link system to help with ease of use, precision, efficiency, and reproducibility. Increased flexion of femoral component and increased total arc of femoral component will be more suitable especially for Asian patients who perform more flexion such as squatting and sitting on the floor in daily living activities.