Do the distal femur and the proximal tibia have narrower aspect ratios in smaller knees? : A morphological analysis of osteoarthritic knees in the Japanese population using computed tomography.

Background: Whether the distal femur and the proximal tibia have narrower aspect ratios in smaller knees has not been clarified. The purpose of this study was to confirm the dimensional characteristics of the distal femur and the proximal tibia using a novel method for consistently determining knee size.

Methods: A total of 220 Japanese osteoarthritic knees (160 female and 60 male knees) were analyzed using computed tomography. The mediolateral (ML) and the anteroposterior (AP) dimensions of the distal femur (fML, fAP) and the proximal tibia (tML, tAP) were measured. The aspect ratios (ML/AP) of the distal femur (fML/fAP) and the proximal tibia (tML/tAP) were assessed against the product of AP × ML as a consistent determination of knee size.

Results: The fML/fAP ratios positively correlated with knee size (fAP × fML) (r = 0.420, p < 0.001), only in the combined cohort, attributable to the narrower aspect ratios of female knees. No correlations were found between the tML/tAP ratios and knee size (tAP × tML) among females, males, nor all subjects (p = 0.299, 0.994, and 0.996, respectively). Aspect ratio correlations to knee size diverged between the three knee size indices, AP, ML, and AP × ML.

Conclusions: AP × ML was the meaningful option for knee size indexing in our morphological analyses. The distal femur, but not the proximal tibia, was found to have a narrower aspect ratio in female knees in the Japanese population.