Capturing deep partial-thickness cartilage loss with semiquantitative scoring: A supplemented MRI Osteoarthritis Knee Score (sMOAKS)

Objective

We propose a supplement to MOAKS (MRI Osteoarthritis Knee Score) for capturing >50 % partial thickness cartilage loss on knee MRI and measure reader agreement.

Design

MOAKS scores 2 severity levels of cartilage damage (any loss, full-thickness loss) within knee subregions with lesional area graded 0–3. We propose supplemented MOAKS (sMOAKS) by adding a similarly graded third level assessment for deep cartilage loss (DCL), >50 % thickness, in addition to traditional MOAKS for improved granularity of partial thickness cartilage loss. Using sMOAKS, two radiologists independently graded cartilage subscores for 40 knees and rescored 20 knees. Consolidated inter-reader and intra-reader agreement was calculated with kappa values for the DCL level supplement. To measure agreement for one example of a more granular combined sMOAKS outcome, coverage probability reader agreement was calculated for a scaled cartilage damage score (CDS), a summed normalized score (0–100) with equal weighting to articular surfaces combining subregion scores.

Results

DCL represented 27.8 % (63/227) of partial but not full-thickness cartilage loss subregion interpretations. Pooled subregion DCL involving >10 % surface area demonstrated 97.7 % (ĸ = 0.71) inter-reader agreement and 98.8 % (ĸ = 0.78) intra-reader agreement. For greatest subregion DCL size, weighted ĸ agreement was 0.73/0.82 (inter-reader/intra-reader) for articular surfaces and 0.75/0.83 for joint compartments. At 90 % CDS intra-reader agreement coverage, inter-reader CDS agreement values were 83 %, 82 %, and 78 % for surfaces, compartments, and whole joints, respectively.

Conclusions

There is substantial agreement for deep cartilage loss detection using sMOAKS across varied analysis methods. Further assessment will determine when the added granularity of sMOAKS is beneficial.