The reliability of a new scoring system for knee osteoarthritis MRI and the validity of bone marrow lesion assessment: BLOKS (Boston Leeds Osteoarthritis Knee Score).

AIM

MRI provides unparalleled visualisation of all the anatomical structures involved in the osteoarthritis (OA) process. There is a need for reliable methods of quantifying abnormalities of these structures. The aim of this work was to assess the reliability of a novel MRI scoring system for evaluating OA of the knee and explore the validity of the bone marrow lesion (BML) scoring component of this new tool.

METHODS

After review of the relevant literature, a collaborative group of rheumatologists and radiologists from centres in the UK and USA established preliminary anatomical divisions, items (necessarily broadly inclusive) and scaling for a novel semi-quantitative knee score. A series of iterative reliability exercises were performed to reduce the initial items, and the reliability of the resultant Boston-Leeds Osteoarthritis Knee Score (BLOKS) was examined. A further sample had both the BLOKS and WORMS (Whole Organ MRI Score) bone marrow lesion (BML) score performed to assess the construct validity (relation to knee pain) and longitudinal validity (prediction of cartilage loss) of each scoring method.

RESULTS

The BLOKS scoring method assesses nine intra-articular regions and contains eight items, including features of bone marrow lesions, cartilage, osteophytes, synovitis, effusions and ligaments. The scaling for each feature ranges from 0-3. The inter-reader reliability for the final BLOKS items ranged from 0.51 for meniscal extrusion up to 0.79 for meniscal tear. The reliability for other key features was 0.72 for BML grade, 0.72 for cartilage morphology, and 0.62 for synovitis. Maximal BML size on the BLOKS scale had a positive linear relation with visual analogue scale (VAS) pain, however the WORMS scale did not. Baseline BML was associated with cartilage loss on both BLOKS and WORMS scale. This association was stronger for BLOKS than WORMS.

CONCLUSION

We have designed a novel scoring system for MRI OA knee, BLOKS, that demonstrates good reliability. Preliminary inspection of the validity of one of the components of this new tool supports the validity of the BLOKS BML scoring method over an existing instrument. Further iterative development will include validation for use in both clinical trials and epidemiological studies.