Page 77 - Imaging of Osteoarthritis and Rheumatoid Arthritis in Hand Joints
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 Accuracy of cartilage MRI of CMC1; comparison with histology
Previous studies have shown that the SPGR sequence is an accurate sequence to image knee joint cartilage.19, 20 While it has been shown that SPGR may overestimate cartilage damage in early OA due to magnetic field inhomogeneity artefacts, a considerable underestimation of cartilage damage has not been reported. In previous studies assessing the accuracy of detection of cartilage defects and/or cartilage volume in the knee using MRI, the patient group either consisted of patients with relatively little damage,19, 21-23 or the areas with severe cartilage damage were not analyzed.14, 24 In the studies of patients with knee OA and relatively little cartilage damage, SPGR MRI had high sensitivity and specificity for detecting cartilage lesions in comparison with arthroscopy19, 23 and very good correlation with cartilage thickness on histology.22
The underestimation of full cartilage loss with MRI was caused by thin layers of 4 high signal on the articular surface that were visible on SPGR MRI, which were interpreted as thin layers of damaged cartilage. On retrospective comparison
of the acquired SPGR and PD images and histology, the thin layers of high
signal intensity on SPGR images were not identifiable on the PD images, and histological examination showed bare bone at the corresponding locations. These thin lines of high signal intensity adjacent to subchondral bone have previously received little attention in knee OA, as the line is very thin compared to the thicker knee cartilage, and has been counted as full-thickness cartilage loss in MRI knee OA studies.25 The same kind of thin lines were previously described by Yoshioka et al.26 in healthy volunteers on the posterior region of the femoral condyle within normal cartilage. The origin of this line is unclear. In our study it may have been caused by an artefact, but we cannot exclude the possibility that it represents a real anatomical substrate such as a loose-lying layer of thin soft tissue, which may be lost during histological preparation.
We recognize that our study has limitations. First, the study design required patients to be scheduled for trapeziectomy, limiting the spectrum of disease severity. However, this is the only feasible method for acquiring in vivo histological specimens of cartilage from the small joints of the hand. To maximize the variation in cartilage status between our subjects, we included all patients undergoing trapeziectomy for treatment of pain and functional impairment, irrelevant of the severity of radiographical osteoarthritis. While we expected to also include some patients with mild cartilage damage, all our patients had severe cartilage damage on histology. Patients with milder OA or pre-clinical OA
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