Overuse of hyaline cartilage and imaging

Traumatic injury to joints may involve articular cartilage alone or result in osteochondral fractures which may impair mechanical properties of articular cartilage. Injuries of articular cartilage alone with visible tissue disruption and osteochondral fractures are now visualized by MRI which is the only modality for direct non-invasive visualization of articular cartilage. Three-dimensional T1-weighted gradient-echo sequences with fat-suppression provide high accuracy in the detection of cartilage surface defects. Fast spin echo imaging with heavy T2-weighting demonstrates cartilage defects in the presence of joint effusion accurately too, but minimal slice thickness in 2D-imaging is limited. For correct staging of osteochondral fractures, which determines further therapy, intraarticular administration of contrast media may be necessary. Repetitive direct blunt trauma or high-energy joint loading can cause cartilage damage without visible tissue disruption. To demonstrate this early stage of chondral injury special techniques and agents are necessary. These include diffusion weighted imaging, measurements of magnetization transfer as a function of collagen concentration, proton density mapping to plot the distribution of water in hyaline cartilage and sodium imaging to visualize ions bound to proteoglycans or intraarticular application of Mangan selectively bound to proteoglycans. Although promising techniques, they are still experimental. With recent developments of repair of cartilage defects by cartilage grafts, osteochondral autografts and transplantation, MRI becomes the method of choice in the noninvasive evaluation of injured articular cartilage and follow-up studies.