Healthy knee asymmetry is a potential risk factor for knee osteoarthritis: Data from the osteoarthritis initiative.

Objective: Commonly used grading systems in knee osteoarthritis (OA) evaluation provide an overview of the disease severity with limited prognostic ability. Recently, efforts towards automated and objective deep- and machine-learning, and computational modeling-based prediction tools have been made, but they are complex and lack interpretability. This study aimed to identify knee joint morphology measures that can be easily quantified from plain radiographs and are indicative of the risk of radiographic OA development among subjects without definite radiographic OA, focusing especially on the asymmetry of the knees. Materials and Methods: Knee joint dimensions and angles were measured from anterior-posterior weight-bearing knee radiographs at baseline and 8-year follow-up time point. The subjects were grouped based on Kellgren-Lawrence grades at the 8-year follow-up and compared with regard to the knee joint dimensions and angles and their asymmetries between the subjects' knees. Results: Absolute dimensions or angles at baseline were not associated with OA development. Instead, the asymmetry in the dimensions (relative difference between the left and right knee), was higher in subjects who developed radiographic knee OA during 8-year follow-up. The medial joint space asymmetry was associated with the development of advanced knee OA when it was over 10 % (OR = 1.87) or 15 % (OR = 3.27). Conclusions: Medial joint space asymmetry between the left and right knee of over 10 % could be a potential risk factor for developing knee OA.