Femoral varus deformity predominates in male Chinese osteoarthritis patients with geographic variability in functional knee phenotypes.

PURPOSE: The aims of this study were to generalise the distribution and sex differences in functional knee phenotypes in a Chinese osteoarthritis (OA) population and to compare the distributions of functional knee phenotypes across geographic regions.

METHODS

Knee phenotypes were evaluated according to Hirschmann's classification in 908 knees with OA, and the correlations among the hip-knee-ankle angle (HKA), femoral mechanical angle (FMA) and tibial mechanical angle (TMA) and their differences between the sexes were described. Studies reporting the distributions of functional knee phenotypes for arthritic knees were included to compare the variability in geographic distribution.

RESULTS

The average values (males, females) of the HKA (173.1 ± 5.4°, 174.0 ± 6.9°), FMA (90.5 ± 2.9°, 91.6 ± 3.5°), and TMA (85.7 ± 3.1°, 85.7 ± 3.6°) demonstrated that the Chinese OA population tended towards femoral and tibial varus deformities in both males and females. A total of 145 functional knee phenotypes were identified in all 908 knees, comprising 68 types in males and 136 types in females. The most common phenotypes were VARHKA6° + VARFMA3° + NEUTMA0° (5.7%) for all knees, VARHKA3° + NEUFMA0° + NEUTMA0° (7.4%) for males and VARHKA6° + VARFMA3° + NEUTMA0° (5.4%) for females. The incidence of femoral varus deformity was greater than that of tibial varus deformity in 48.4% of males and 36.5% of females, and the incidence of tibial varus deformity was greater than that of femoral varus deformity in 24.7% of males and 35.2% of females. Seven studies including 16,395 knees were identified. The main femoral and tibial phenotypes in different geographic regions were VARFMA3° and NEUTMA0°, but their proportional distributions differed significantly.

CONCLUSIONS

Sex differences in the functional knee phenotypes of OA patients in China were identified. Femoral varus deformity was more common than tibial varus deformity in males, whereas the difference was minimal in females. Moreover, functional knee phenotypes varied significantly across geographic regions.

LEVEL OF EVIDENCE: Level IV.