Pakpoom Ruangsomboon, Jirayu Paugchawee, Rapeepat Narkbunnam, Keerati Chareancholvanich, Chaturong Pornrattanamaneewong

Division of Adult Reconstructive Surgery, Department of Orthopaedic Surgery, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand

Keywords: Femoral component size, Oxford Phase 3 unicompartmental knee arthroplasty, prosthetic size and height, sex distribution, Thailand.


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.

Citation: Ruangsomboon P, Paugchawee J, Narkbunnam R, Chareancholvanich K, Pornrattanamaneewong C. The factors influencing the component sizes in Oxford Phase 3 unicompartmental knee arthroplasty. Jt Dis Relat Surg 2022;33(3):505-512.

Ethics Committee Approval

The study protocol was approved by the Siriraj Institutional Review Board (SIRB) Ethics Committee (date: September 18, 2021, no: 722/2021). The study was conducted in accordance with the principles of the Declaration of Helsinki.

Author Contributions

Idea/concept, analysis and/or interpretation, literature review, writing the article, references and fundings, materials: C.P., P.R.; Design: C.P.; Control/ supervision: K.C.; Data collection and/or processing: J.P., R.N.; Critical review: K.C., R.N.

Conflict of Interest

The authors declared no conflicts of interest with respect to the authorship and/or publication of this article.

Financial Disclosure

The authors received no financial support for the research and/or authorship of this article.


The authors thank Miss Nichakorn Khomawut for her support with data collecting and statistical analysis. We also appreciate Onlak Ruangsomboon, MD, and Kevin P. Jones for their assistance in revising the initial draft.