Distribution of coronal plane alignment of the knee and functional knee phenotype classification in the Thai arthritic population and correlation with other Asian populations.

Abstract

The Coronal Plane Alignment of the Knee (CPAK) and Functional Knee Phenotype (FKP) classification system categorize knee phenotypes into subtypes. It has been proposed that maintaining constitutional knee alignment in knee arthroplasty may enhance outcomes. Therefore, this study aimed to examine the phenotypic distribution in a Thai population using the CPAK and FKP classifications and its correlation with other Asian populations. This retrospective cohort study included 509 patients who underwent knee arthroplasty. Long-leg standing weight-bearing radiographs were used to categorize patients according to the CPAK (arithmetic hip-knee-ankle angle [aHKA], joint-line obliquity [JLO]) and FKP (hip-knee-ankle angle [HKA], femoral mechanical angle [FMA], and tibial mechanical angle [TMA]) classification system. The most common CPAK distribution was type I (49.3%), followed by type II (20.6%) and type IV (11.0%). In males, CPAK Types I and II were the most common, similar to females; however, males had a significantly higher rate of Type I than females (58.8% vs. 46.5%, p = 0.049). The most frequent FKP was VAR_HKA6°VAR_FMA3°VAR_TMA3° (10%), VAR_HKA3°VAR_FMA3°NEU_TMA0° (7.7%), and NEU_HKA0°NEU_FMA0°NEU_TMA0° (7.1%). Thai arthritic knees predominantly exhibited apex distal JLO with constitutional varus alignment, consistent with findings from other Asian populations. There were no significant differences in CPAK distribution between TKA and UKA patients; however, aHKA and lateral distal femoral angle were significantly different between groups. The Thai arthritic population demonstrates a significant trend toward apex distal JLO and varus alignment, aligning with findings from other Asian populations, which aids in the personalization of knee arthroplasty approaches.