There are two widely used scoring systems for knee magnetic resonance imaging (MRI) in osteoarthritis (OA) and the strengths and weaknesses of each system in terms of ease of use and association with known risk factors and outcomes are unknown.
To compare Whole Organ Magnetic Resonance Imaging Score (WORMS) and Boston Leeds Osteoarthritis Knee Score (BLOKS) scales using longitudinal MRI and X-ray data.
In the Osteoarthritis Initiative (OAI), knee radiographs, long limb films for alignment and MRI's were acquired in the interval from 0 to 24 months follow-up. OAI MRI's from baseline and 24 months were read separately using BLOKS and WORMS scales. X-rays were scored semiquantitatively for joint space loss and long limb films were measured for alignment angle. We evaluated which of the WORMS or BLOKS cartilage loss scores best correlated with joint space loss on the X-ray and which was best predicted by varus malalignment on long limb film. To examine the validity of bone marrow lesion (BML) and meniscal scales, we tested which of WORMS or BLOKS baseline scores for BML or meniscus best predicted cartilage loss from baseline to 24 months. We critically evaluated strengths and weaknesses of each scoring system also.
Of 113 knees read longitudinally, 33 showed any cartilage loss using BLOKS and 30 using WORMS with high agreement between the scales. In the medial compartment, both BLOKS and WORMS picked up only 42% of the knees with X-ray joint space loss with similar specificity (88 vs 86%). Varus knees were more likely to be a risk factor for medial cartilage loss in BLOKS [adj odds ratio (OR) 5.9 (95% confidence intervals (CIs) 1.5, 24.0)] than in WORMS [adj OR 2.1 (95% CI 0.7, 6.3)]. WORMS BML scores predicted cartilage loss more strongly than any BLOKS BML variables and some BLOKS BML measures did not affect risk of cartilage loss at all. However, across the range of scores, meniscal tear scores in BLOKS predicted cartilage loss better for each abnormality than did WORMS meniscal tear scores and the meniscal signal abnormality scored in BLOKS but not in WORMS, predicted cartilage loss. BLOKS took longer and was more difficult to score longitudinally especially for BML scores.
In a comparison of instruments limited by small numbers of knees compared, BLOKS meniscal score was preferable to WORMS meniscal scale in predicting cartilage loss most likely because it includes potentially important pathology missed by WORMS. On the other hand, BML scoring in WORMS was preferable in that it better predicted later cartilage loss, was easier to score and did not include potentially extraneous measures. Neither method was definitively better for cartilage scoring.