The factors influencing the component sizes in Oxford Phase 3 unicompartmental knee arthroplasty

Abstract

Objectives: This study aims to investigate the Thai population characteristics that may correlate the component sizes used in the Oxford Phase 3 unicompartmental knee arthroplasty (OUKA) and to examine common matching patterns and variables affecting matching and patient-specific factors while determining the femoral component (Fc) size for Thai patients. Patients and methods: Between June 2003 and June 2019, a total of 773 knees of 773 patients (145 males, 628 females; median age: 64.0 years; range: 44 to 86 years) who underwent OUKA using Oxford Microplasty® Instrumentation were retrospectively analyzed. The femoral and tibial components (Tc) were matched based on the patient's age, sex, height, weight, and other characteristics. The Fc sizes were compared in terms of patient characteristics. Also, the area under the receiver operating characteristic (AuROC) was calculated. Results: A total of 6.5% of the Fcs were extra small (XS), 65.7% were small (S), 20.6% were medium (M), 7.2% were large (L), and 0% were extra-large (XL). For Tc sizes, the distribution was as follows: 20.2% AA; 31.6% A; 24.3% B; 16.3% C; 6.0% D; 1.7% E; and 0% F. Females had the most common Fc and Tc sizes of S and A, while males had the most common sizes of M and C. The S-A (32.3%) and M-C (27.5%) were the most often used matching patterns among females and males, respectively. Sex, body weight (BW), height, and body mass index (BMI) were independent predictors of Fc sizes. The AuROC for BW, height, and BMI was statistically significant. Conclusion: The S and A for females and M and C for men were the most common sizes of Fc and Tc in Thai patients. Among females, the most prevalent pairing was S-A and, among men, it was M-C. The strongest determinants of Fc sizes were found to be male sex and height.