Femoral Component Sizing in Oxford Unicompartmental Knee Replacement: Existing Guidelines Do Not Work for Indian Patients

Oxford unicompartmental knee replacement (OUKR) has shown excellent long-term clinical outcomes as well as implant survival when used for correct indications with optimal surgical technique. Anteromedial osteoarthritis is highly prevalent in Indian patients, and OUKR is the ideal treatment option in such cases. Uncertainty prevails about the best method to determine femoral component size in OUKR. Preoperative templating has been shown to be inaccurate, while height- and gender-based guidelines based on European population might not apply to the Indian patients. Microplasty instrumentation introduced in 2012 introduced the sizing spoon, which has the dual function of femoral component sizing and determining the level of tibia cut. We aimed to check the accuracy of sizing spoon and also to determine whether the present guidelines are appropriate for use in the Indian patients. A total of 130 consecutive Oxford mobile bearing medial cemented UKR performed using the Microplasty instrumentation were included. The ideal femoral component size for each knee was recorded by looking for overhang and underhang in post-operative lateral knee radiograph. The accuracy of previous guidelines was determined by applying them to our study population. Previously published guidelines (which were based on Western population) proved to be accurate in only 37% of cases. Hence, based on the demographics of our study population, we formulated modified height- and genderbased guidelines, which would better suit the Indian population. Accuracy of modified guidelines was estimated to be 74%. The overall accuracy of sizing spoon (75%), when used as an intraoperative guide, was similar to that of modified guidelines. Existing guidelines for femoral component sizing do not work in Indian patients. Modified guidelines and use of intraoperative spoon should be used to choose the optimal implant size while performing OUKR in Indian patients.