Oxford Phase 3 Unicompartmental Knee Arthroplasty in Thailand: Distribution of Prosthetic Size and Height Based on Gender Distribution of Femoral Component Size

Abstract Introduction: Survivorship of Oxford phase 3 unicompartmental knee arthroplasty (OUKA) is strongly influenced by the size of the femoral component (Fc) and the tibial component (Tc) that are selected. The distribution of prosthetic size, and guidelines to determine the ideal Fc size have been mainly studied in Western population. The aim of this study was to determine the distribution of OUKA prosthetic size, and to investigate the factors that significantly influence the selection of Fc size in Thai patients.Methods: This retrospective study included 773 OUKA that were performed using Oxford Microplasty® Instrumentation during 2003-2019. Patient age, gender, side, body weight (BW), height, body mass index (BMI), size of femoral and tibial components, and the matching between components were recorded. The distribution of implant size and their matching was analyzed. Patient characteristics were compared among the Fc sizes. Area under the receiver operating characteristic (AuROC) curve was calculated to measure the performance of significant continuous variables for determining Fc size.Results: The distribution of Fc size was extra-small (XS) 6.5%, small (S) 65.7%, medium (M) 20.6%, large (L) 7.2%, and extra-large (XL) 0%. The distribution of Tc size included AA 20.2%, A 31.6%, B 24.3%, C 16.3%, D 6.0%, E 1.7%, and F 0%. The most common Fc and Tc sizes in females was S and A, respectively, and in males M and C, respectively. The most common matching pattern used in females and males was S-A (32.3%) and M-C (27.6%), respectively. Concerning factors that influence Fc prediction, we found significant differences in gender, BW, height, and BMI among the Fc sizes. After calculating the AuROC for BW, height, and BMI, we found height to have the highest AuROC with statistical significance. Height based on gender distribution was also analyzed.Conclusion: In Thai patients, the predominant size of Fc was S for females, and M for males. The predominant size of Tc was A for females, and C for males. The most common matching pattern was S-A for females, and M-C for males. Gender and height were identified as the factors that most strongly influence the prediction of Fc size.