Specific functional knee phenotypes are associated with increased osteoarthritis progression: A ≥10-year longitudinal study.

PURPOSE: To evaluate osteoarthritis (OA) progression across functional knee phenotypes (FKPs) over a follow-up period of ≥10 years. METHODS: This retrospective longitudinal study included 388 patients (764 knees) with healthy knees or early OA (Kellgren-Lawrence grade ≤1) at baseline and a minimum follow-up of 10 years. FKPs were classified based on the hip-knee-ankle angle (HKA), femoral mechanical angle (FMA) and tibial mechanical angle (TMA) obtained from orthoradiographs. A total of 72 FKP groups were identified, of which 15 groups with a sample size ≥20 (511 knees) were finally selected for analysis. OA progression was defined as an increase in at least one Kellgren-Lawrence grade during follow-up. The OA progression rates for each FKP group were compared with those of the neutral reference group (NEUHKA0° NEUFMA0° NEUTMA0°) as exploratory analyses. Finally, multivariate generalized estimating equation logistic regression analysis was performed to identify factors associated with OA progression. RESULTS: Over a follow-up period of ≥10 years, the neutral reference group showed an OA progression rate of 52.4% (44/84). Three phenotypes showed significantly higher OA progression rates compared with the reference phenotype: VARHKA3°VARFMA3° NEUTMA0° (88.9% [32/36]; odds ratio [OR], 7.27; 95% confidence interval [CI], 2.36-22.38; p < 0.001), VALHKA3° NEUFMA0°VALTMA3° (84.6% [22/26]; OR, 5.00; 95% CI, 1.59-15.76; p = 0.005) and NEUHKA0°VARFMA3°VALTMA3° (75.0% [24/32]; OR, 2.73; 95% CI, 1.10-6.76; p = 0.035). In the multivariate analysis, the three FKP categories were also significantly associated with increased risk of OA progression (VARHKA3°VARFMA3° NEUTMA0° (adjusted odds ratio [aOR], 6.54; 95% CI, 2.20-19.41; p < 0.001), VALHKA3° NEUFMA0°VALTMA3° (aOR, 7.50; 95% CI, 1.82-30.95; p = 0.005) and NEUHKA0°VARFMA3°VALTMA3° (aOR, 3.10; 95% CI, 1.17-8.20; p = 0.023). CONCLUSIONS: Specific FKPs are associated with a significantly increased risk of OA progression compared with the neutral phenotype. OA progression appears to be influenced not only by overall limb alignment but also by combined femoral and tibial alignment patterns. LEVEL OF EVIDENCE: Level III.