Osteochondral injuries represent a spectrum of articular conditions ranging from acute cartilage injury to chronic osteochondral defects, including osteo-chondritis dissecans (OCD). In approaching osteochondral injuries, it is useful to conceive of the cartilage and subchondral bone as a functional unit, which in addition to cartilage and bone consists of the bone/cartilage interface or tidemark zone. Although there is ongoing debate regarding the pathogenesis of OCD, there is a general consensus supporting a traumatic/mechanical theory of injury to the bone/cartilage complex. As such, the imaging appearance of chon-dral/osteochondral injury differs, based on the severity and acuity of the trauma, and the reparative response of the tissue. A single episode of high-impact trauma may result in a chondral or osteochondral fracture. In certain locations, with appropriate mechanisms of injury, the forces applied to the bone/cartilage unit result in a debonding or delamination of the cartilage from the underlying bone. Acute trauma may alter the biomechanical properties of the bone/cartilage complex, leading to progressive focal loss of articular cartilage and degenerative change in the subchondral bone. In the absence of an acute traumatic insult, chronic repetitive microtrauma may produce focal microfracture, necrosis, and healing response of subchondral bone, with localized degenerative changes in the overlying cartilage resulting in OCD. These lesions have implications for the entire joint, because the presence of focal chondral and osteochondral defects has been identified as a significant risk factor for progressive articular damage leading to osteoarthritis [51,52].
The historical dependence on radiography has emphasized the osseous component of osteochondral injuries. With development of MRI, there is the ability to detect and monitor changes in the articular cartilage that occur with acute and chronic injuries. Recognizing chondral/osteochondral injuries is important, because they may be an isolated source of persistent pain following trauma, or they may be associated with a recognized pattern of soft-tissue injuries. Treatment approaches for osteochondral injury are based on determination of lesion site, age, and likelihood of progression. With the potential development of chondroprotective therapies, recognizing early signs of osteochondral injuries is likely to become even more important in the future.
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