Page 93 - Imaging of Osteoarthritis and Rheumatoid Arthritis in Hand Joints

High-resolution MRI of cartilage in finger joints
Discussion
Using the high resolution MRI (hrMRI) cartilage score the readers identified more joints with cartilage damage in comparison with inter bone distance loss in the OA group, and less joints with cartilage damage in the healthy control group. Reliability of both scores were comparable.
Large variations of cartilage thickness and shape were present in both OA
patients and the controls. The shape and thickness of the healthy cartilage
layer showed considerable differences. For example, some healthy controls had considerably thinner cartilage centrally on the metacarpal head than on the
rest of the metacarpal head. These variations make it challenging to distinguish
normal vs. minor cartilage loss in cross sectional imaging studies in early hand
OA, especially without a reference for the individual patient. This also occurs
when inter bone distance scoring is used on thick slices, as thick slices have
more partial volume averaging. Scoring on these thick slices is therefore more
prone to underestimate cartilage damage in asymmetric damaged cartilage 5 layers and may overestimate narrowing in patients with normal relatively
thin cartilage layers, in comparison with direct cartilage imaging. Our results therefore suggest that direct evaluation of cartilage with hrMRI is more accurate for cartilage assessment.
The observed pattern of cartilage loss in our patients was overall diffuse loss of cartilage thickness over large areas of the joint. Small focal cartilage lesions with abrupt edges which have been observed in the knee17, 18 were not detected in our study. The lowest grade of cartilage damage in our proposed scoring system (single abrupt focal cartilage damage lesion <10% of surface area) was included in analogy to the MOAKS scoring system in the knee 13, but not scored. Our results may suggest that either the normal pattern of cartilage loss in hand OA consists of more gradual and continual cartilage loss, or we are unable to see small focal lesions, even with our hrMRI images. Future studies using this or a similar hrMRI cartilage score should therefore consider removing this grade from the score.
This study adds to the available knowledge on hrMRI of small finger joints. We used a 3T MRI machine in combination with a special MRI coil as a normal
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