Summary

There is a broad variation of functional knee phenotypes present in knees affected by lateral compartment OA, with gender-specific and age-related differences.

Abstract

Introduction

In recent years, there has been an increasing interest in understanding lower limb alignment and knee phenotypes in both non-arthritic and arthritic knees, recognizing the limitations of traditional approaches that lack sophistication by overlooking the knee joint line orientation. The primary aim of this study was to assess and describe the phenotypic variation in the coronal plane of knees affected by symptomatic isolated lateral compartment osteoarthritis (OA). The secondary aim of this study was to investigate the potential gender-specific and age-related differences in functional knee phenotypes among knees with lateral compartment OA.

Methods

The Hirschmann classification system was used to categorize 305 knees with isolated lateral compartment OA into distinct functional knee phenotypes based on their femoral mechanical angle (FMA), tibial mechanical angle (TMA) and mechanical hip-knee-ankle angle (mHKA).
The phenotypic variation of functional knee phenotypes, femoral and tibial phenotypes, and knee phenotypes (i.e., the combination of femoral- and tibial phenotypes), was assessed for the entire cohort and stratified by gender and age categories (i.e., patients <50 years, 50 to 70 years, and >70 years).

Results

Among knees with lateral compartment OA, a total of 60 distinct functional knee phenotypes were identified, with phenotype VALHKA6º NEUFMA0º VALTMA3º being the most prevalent (10.8% of knees). The coronal deformity predominantly presented as an isolated tibial valgus deformity, with 37.4% of knees exhibiting this specific deformity. Gender-specific differences were evident, with females exhibiting significantly greater valgus alignment in both mHKA and TMA values compared to males (mHKA: -6.4 vs. -5.4, respectively; p = 0.02 and TMA 94.4 vs 89.0, respectively; p = .005). Age-related variations included younger patients (i.e., <50 years) predominantly displaying femoral deformities, while older patients (i.e., >50 years) primarily manifested isolated tibial- or combined femoral and tibial deformities.

Conclusion

There is a broad variation of functional knee phenotypes present in knees affected by lateral compartment OA, with gender-specific and age-related differences. Acknowledging this inherent phenotypic variation in lateral compartment osteoarthritic knees may have important implications for enhancing preoperative planning and improving personalized alignment strategies in knee arthroplasty.