How to define subregional osteoarthritis progression using semi-quantitative MRI osteoarthritis knee score (MOAKS)

Recently, the MRI Osteoarthritis Knee Score (MOAKS), a new semi-quantitative magnetic resonance imaging (MRI) scoring tool, was introduced by a panel of experienced researchers in osteoarthritis (OA). The MOAKS is primarily applicable to quantify OA status, since the interpretation of change in the MOAKS features was not described. In order to enable longitudinal evaluation, we propose definitions for progression and improvement of the main MOAKS features.

Clear definitions for progression and improvement of the main MOAKS features are given in this brief report. 687 baseline and 30 months follow-up MRIs of the knees of 348 overweight and obese middle-aged women, free of OA at baseline, were scored using the MOAKS. Baseline prevalence and the change of MOAKS features after 30 months follow-up, based on our definitions for progression and improvement, are presented.

The proposed definitions showed 3% to 23% progression and 0% to 11% improvement in the MOAKS features during the 30 months follow-up. Overall, progression rates were higher in the medial than in the lateral tibiofemoral (TF) joint. Progression of bone marrow lesions (BMLs) and cartilage defects was highest in the patellofemoral (PF) joint. Inter-rater reliability of the MOAKS scores was moderate to nearly perfect (PABAK 0.77-0.88), with high percentage of agreement overall (89-94%).

This brief report presents definitions for progression and improvement of the main MOAKS features for the longitudinal evaluation of knee OA features on MRI. We advocate uniform usage of the proposed definitions across studies, but welcome suggestions for optimization.