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Diagnosis of Cartilage Lesions

Much effort has been directed at the development of imaging techniques that effectively diagnose cartilage lesions in the shoulder. The thrust of the research has employed a variety of magnetic resonance imaging techniques to delineate not only the actual lesions, but also something about their physiology.

It is well established that cartilage functions as the load-bearing surface in the joints of the musculoskeletal system. Major macromolecules in cartilage are collagen Type II and proteoglycans. Although proteoglycans provide much of the compressive stiffness through electrostatic repulsion, collagen provides tensile and shear strength. Several studies have shown that the earliest stages of cartilage degeneration are primarily associated with loss of proteoglycan and minor changes in collagen structure.

In one study, bovine articular cartilage was analyzed with a variety of MR parameters including T2 relaxation rates and spine-lattice relaxation times in the rotating frame (T1ρ) mapping method. The findings included a significant correlation between the changes seen on T1ρ mapping and the sequential depletion of proteoglycan. Studies like these have served to expand the base of knowledge with regards to grading of articular lesions.

Although arthroscopy is the so-called gold standard at this point for final determination of the management of these lesions, it would be ideal to have a noninvasive modality that fully assesses the lesions.

In the clinical setting, it is important to be able to delineate the presence of cartilage lesions with some certainty. There are several studies available in the literature that give some guidance. In one study, a double blind prospective study of 15 patients with anterior shoulder instability were analyzed with respect to the efficacy of MRI versus arthroscopy in the evaluation of chondral or osteochondral lesions of the humeral head .

MR produced 6 true positives, 5 true negatives, and 4 false negatives for an accuracy and sensitivity of 60% and 87%, respectively. Arthroscopy gave 8 true positives, 5 true negatives, and 2 false negatives, with a sensitivity of 80% and an accuracy of 87%. All lesions diagnosed with either method were regarded as positive by definition, with the result that the specificity was always 100%.

The differences in diagnosis sprang from the false negatives. As a result of the variable ability to identify the cartilage lesions prospectively, it was advised that both of these methods should be employed to ensure the correct diagnosis, and hence the correct choice of treatment.

Another study has described the MRI findings of focal articular cartilage lesion of the superior humeral head in seven patients. This was a retrospective study to evaluate the location and incidence of these lesions. The lesions occurred along the superior surface of the posterior humeral head (medial to the expected location of a Hill-Sachs lesion), were caused by trauma, and did not seem to have a specific mechanism of injury. It was felt that they may cause clinical symptoms and may be easily overlooked on MRI because they were missed on six out of seven of those encountered.

In the largest available study, Guntern et al. It determined the prevalence of articular cartilage lesions in a group of patients. Arthrographic images obtained in 52 consecutive patients with a mean age of 45.8 years were retrospectively evaluated for glenohumeral cartilage lesions. Two experienced musculoskeletal radiologists who were blinded to the arthroscopy report independently analyzed the articular cartilage. Humeral and glenoidal cartilage were assessed separately and arthroscopic findings were used as the standard of reference.

At arthroscopy, humeral cartilage lesions were found in 15 patients (frequency, 29%). Four lesions were subtle, and 11 were marked. Cartilage lesions of the glenoid were less frequent (eight patients; frequency, 15%): Three were subtle, and five were marked. For reader 1 and reader 2, respectively, sensitivity of MR arthrography for humeral cartilage lesions was 53% and 100%, specificity was 87% and 51%, and accuracy was 77% and 65%; sensitivity for glenoidal cartilage lesions was 75% and 75%, specificity was 66% and 63%, and accuracy was 67% and 65%.

Interobserver agreement for the grading of cartilage lesions with MR arthrography was fair (humeral lesions, kappa = 0.20; glenoidal lesions, kappa = 0.27). Based on the study, it was felt that the performance of MR arthrography in the detection of glenohumeral cartilage lesions is moderate with a high degree of variability associated with the interpretation of the images.

As can be discerned by this analysis, much work needs to be done in the delineation of cartilage lesions on a prospective basis. While the use of gadolinium-enhanced arthrograms has clearly improved the ability to find these lesions, a significant proportion is not identified prospectively.

Also, the biological parameters that are discernible with the use of MRI technology are important to consider. The ideal study that addresses not only the presence of a cartilage lesion, but also something about its biology or reparative capability is clearly within the grasp of modern imaging. Its implementation and refinement, however, await further studies.

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