Imaging of osteochondral injuries

Detecting articular cartilage defects in the knee is important because the signs and symptoms associated with such defects can be confused clinically with meniscal tears, synovial problems, and extensor mechanism dysfunction.(19) Unfortunately, cartilage is not visualized on conventional radiodraphs. Therefore, purely chondral lesions require standard arthrography, computed arthrotomography, magnetic resonance (MR) arthrography, or arthroscopy for accurate diagnosis. Unless there is a large free fragment, standard arthrography and computed arthrotomography are often nondiagnostic. MR imaging has been used to evaluate articular cartilage, although adequate imaging of articular cartilage remains difficult owing to the nonuniform composition of its structural architecture. In the past, many MR imaging techniques have been applied to the assessment of articular cartilage. A standard spin-echo MR imaging technique alone is generally inadequate to evaluate articular cartilage. Standard spin-echo technique combined with fat suppression has the added advantage of improving contrast between cartilage and fluid; however, it too is inadequate. Most simple gradient echo sequences do not allow detection of superficial or minor lesions of articular cartilage. A more advanced gradient echo technique has been developed, which has been advocated as the optimal technique for evaluation of cartilage; it is a spoiled gradient echo sequence using fat suppression and three-dimensional (3D) acquisition (SPGR) (Fig. 1). With this sequence, spatial resolution is high owing to the ability to obtain thin contiguous slices; the images can be reformatted in multiple planes; and there are high contrast-to-noise ratios between cartilage and fluid and between cartilage and bone(17) (Fig.2). Using SPCR MR imaging, the trilaminar appearance of the articular cartilage can be seen. The technique can be used to evaluate cartilage degeneration, demonstrating loss of signal in a superficial bright layer and varying degrees of loss of signal in intermediate and deep layers within the cartilage. Other MR imaging techniques used for cartilage analysis are subtraction magnetization-transfer contrast in-caging, short echo time projec-evidence of cartilage abnormality on MR images relates to the identification of fluid at the interface between the fragment and the parent bone. The MR imaging technique influences dramatically whether such fluid is identified. MR arthrography employing the intra-articular injection of gadolinium compounds can be advantageous in the delineation of the chondral surface and in the detection of intraarticular bodies. Optimally, MR imaging would allow direct analysis of the cartilage surface, and specific imaging sequences that are most suited to this analysis are still evolving.