Application of shear forces to the cartilage/bone interface can injure the tide-mark zone and disrupt collagen fibers that bind the cartilage to the subchondral bone. In addition to shear force applied directly to the articular surface, high shear strain at the bone cartilage interface develops with axial compression . Disruption of the collagen fibers leads to delamination or debonding of cartilage from the underlying bone. Cartilage delamination may not be readily apparent at arthroscopy because the articular surface is often intact . In addition to biomechanical factors, recent evidence demonstrates that genetic factors influence the risk of cartilage delamination .
As illustrated in Fig. 7, MRI findings of cartilage delamination consist of linear T2 elevation at the bone cartilage interface . This is likely caused by focal elevation in water content, as well as loss of collagen fiber aniosotropy in the radial zone that occurs when cartilage is cleaved from bone . These injuries are best seen on T2- or PD-weighted images with fat saturation. Recently MR arthrography has been used to assess acetabular cartilage delamina-tion in the hip. With this technique, cartilage delamination was indicated by the presence of high signal on T1-weighted, fat suppressed images between bone and cartilage . This technique has not been explored in the knee or ankle. In the knee, delamination injuries may be seen in the femoral condyle, frequently in cartilage adjacent to the posterior horn of the meniscus. In the setting of patellar dislocation, shearing injury can lead to delamination injuries of the median patellar ridge, and may be associated with full-thickness cartilage
fissures or flap tears. Delamination injuries are also frequently observed in the femoral trochlea following blunt anterior knee trauma, often in association with patellar cartilage injury (Fig. 8).
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