[Imaging of cartilage]

The motivation for cartilage repair is the preservation of adequate joint motion. Repairing joint surface congruity and providing balanced load bearing are crucial for this. MRI can contribute to this goal by describing number, depth, size, and distribution of cartilage lesions throughout the different joint compartments. Essential to such a contribution are adequate spatial resolution at a reasonable SNR together with good contrast between both cartilage and the subchondral bone as well as the joint space. For TSE sequences, this is achieved using TEs between 30 and 50 ms. Diagnostic accuracy is optimal when a lesion is depicted in more than one plane. Short TE, high bandwidth, and the appropriate orientation of the frequency encoding direction contribute to minimizing metal artifacts. Besides internal alterations of the cartilage's matrix, moderately T2-weighted TSE sequences sensitively depict bone marrow edema such as signal alterations and joint effusion, both contributing to highlight even subtle cartilage lesions. T1-weighted FS/WE 3D GE sequences profit from their high spatial resolution to appreciate gradual erosion of the cartilage. In OD the interface to the surrounding bone, the integrity of the overlying cartilage, and associated cysts are used to determine stability. The presence of two or more findings increases diagnostic accuracy. Prognosis is associated with the size of the affected area.