Chondral lesions of the patella evaluated with computed tomography, magnetic resonance imaging, and arthroscopy.

In a small series of cadaver knees, experimentally created lesions of the patellar cartilage were compared using contrast computed tomography (CT) and magnetic resonance (MR) imaging. Contrast CT was able to recognize only 50% of the lesions smaller than 3-mm diameter at the first attempt, and none of the lesions of 0.8 mm. MR imaging detected all the lesions, even those as small as 0.8 mm, without use of contrast material. Simultaneously, a prospective clinical study comparing MR diagnoses of chondral lesions with arthroscopic findings was initiated in a series of 54 knees. This clinical study revealed that, concerning patellar chondral lesions, the accuracy of MR imaging compared with arthroscopy (the gold standard) was 81.5%. The sensitivity was 100%, but the specificity only 50% due to the false positives. Reexamination of the MR records enabled us to refine the MR diagnosis and to propose a staging of the chondral lesions. The high rate of false-positive results in our series can be explained by the hypothesis that MR imaging can possibly detect very early lesions, which appear as abnormalities in the deep cartilage layers.