Coronal T1-weighted, proton-density–weighted fat-suppressed, and sagittal T2-weighted fat-suppressed MR images (left to right in each row of a, b, and c) at presentation (a) show extensive bone marrow edema (* in a), hypointense fracture lines, and areas of low signal intensity subjacent to the subchondral bone plate (arrowheads in a) associated with minimal flattening of the articular surface; images obtained 6 months later (b) show articular surface collapse (black arrow in b) associated with numerous cystlike areas (white arrow in b) and marrow edema confined to the periarticular region; images obtained at 16 months (c) show that a large saucerized articular surface defect has formed (arrows in c). 4.1 (a)–(c) Select sagittal, coronal, and axial T2 images from a 3-T MRI of the right knee without contrast. This article provides a comparative analysis of several of the most common entities that manifest as osteochondral lesions of the knee, in particular of the femoral condyles. †See text for description of specific features. Coronal T1-weighted, proton-density–weighted fat-suppressed, and sagittal T2-weighted fat-suppressed MR images (left to right in each row of a, b, and c) at presentation (a) show extensive bone marrow edema (* in a), hypointense fracture lines, and areas of low signal intensity subjacent to the subchondral bone plate (arrowheads in a) associated with minimal flattening of the articular surface; images obtained 6 months later (b) show articular surface collapse (black arrow in b) associated with numerous cystlike areas (white arrow in b) and marrow edema confined to the periarticular region; images obtained at 16 months (c) show that a large saucerized articular surface defect has formed (arrows in c). A contained grade IV lesion measuring approximately 8 mm involving the lateral femoral condyle. The bone right underneath the cartilage will also be injured. (b–d) Sagittal T2-weighted fat-suppressed MR image (b), proton-density–weighted MR image (c), and CT image (d) show a curvilinear fracture (arrow in b and c) encircling a portion of subchondral bone and overlying cartilage. Although definitive evidence is lacking, when osteonecrosis is found in OCD, it actually may be secondary to fragment detachment and loss of blood supply rather than the primary cause of its formation (41,43,45,50). A localized osteochondral defect can be created acutely or can develop as an end result of several chronic conditions. OCD in an 18-year-old man who heard a pop while getting out of bed and was unable to extend his knee. (d) MR image obtained 6 months later shows restoration of the subchondral bone plate (arrowhead). Figure 9a. In early uncomplicated AVN, the marrow signal in the infarct is preserved, representing mummified fat, and there is no surrounding bone marrow edema. Figure 17a. The most common histologic findings in bone marrow edema-like lesions include bone necrosis, fibrosis, hemorrhage, and trabecular abnormalities, while edema is infrequent (64–66). Subchondral bone plate collapse, demonstrated by the presence of a frank depression or a fluid-filled cleft, can be seen in advanced stages of both AVN and SIF, indicating irreversibility. Coronal T1-weighted, proton-density–weighted fat-suppressed, and sagittal T2-weighted fat-suppressed MR images (left to right in each row of a, b, and c) at presentation (a) show extensive bone marrow edema (* in a), hypointense fracture lines, and areas of low signal intensity subjacent to the subchondral bone plate (arrowheads in a) associated with minimal flattening of the articular surface; images obtained 6 months later (b) show articular surface collapse (black arrow in b) associated with numerous cystlike areas (white arrow in b) and marrow edema confined to the periarticular region; images obtained at 16 months (c) show that a large saucerized articular surface defect has formed (arrows in c). The overall extent of meniscal abnormality and cartilage loss in the joint and decreased knee range of motion at the time of presentation are associated with clinical progression (21). Figure 6a. Osteochondral fracture in a 32-year-old man with a hyperextension injury associated with a posterior cruciate ligament tear (not shown). The multicenter study group Research in OCD of the Knee (ROCK) recently has proposed a radiographic classification system to improve interobserver reliability (54). Classic SIF in a 64-year-old man. These criteria were revised for juvenile OCD (62) with the addition of three secondary signs that all showed 100% specificity: (a) a T2-weighted high-signal-intensity rim surrounding a juvenile OCD lesion indicates instability only if it has the same signal intensity as that of joint fluid, (b) a second outer rim of T2-weighted low signal intensity, or (c) multiple breaks in the subchondral bone plate on T2-weighted MR images (Fig 18). Cysts surrounding a juvenile OCD lesion indicate instability only if they are multiple or larger than 5 mm (62). Osteonecrosis of the knee can be encountered in epiphyseal or subarticular bone, where it is referred to as an AVN, and in the metadiaphysis, where the term bone infarction is often applied. Figure 19a. Two misconceptions contributed to a long evolution of the understanding of this disorder: (a) a pre–MRI-era hypothesis that attributed it to a primary AVN, resulting in the misnomer, and (b) an effort to distinguish it fundamentally from SIF, largely impelled by differences in prognosis. The advent of new procedures for repairing cartilage in knee and ankle joints has increased the need for accurate noninvasive methods to objectively evaluate the success of repair. They typically are associated with a history of trauma; however, nontraumatic etiologies have been described. Full-thickness cartilage loss is present (arrowheads), accompanied by subchondral sclerosis (immediately under the tissue near the arrowhead in a). These are essential findings to acknowledge in patients with acute traumatic injuries and SIF. Note the macerated and extruded medial meniscus (black arrow in b). Figure 5b. Subchondral bone plate collapse, demonstrated by the presence of a depression or a fluid-filled cleft, can be seen in advanced stages of both avascular necrosis and subchondral insufficiency fracture, indicating irreversibility. Common entities include acute traumatic osteochondral injuries, subchondral insufficiency fracture, so-called spontaneous osteonecrosis of the knee, avascular necrosis, osteochondritis dissecans, and localized osteochondral abnormalities in osteoarthritis. (b) Coronal MRimage in the same patient obtained 2 years earlier shows the normal appearance of the subchondral bone plate (arrow). Radiographs of the right knee demonstrate open growth plates and a well circumscribed 1x1cm area of sclerotic subchondral bone with a radiolucent halo separating this area from his femoral epiphysis. Note articular surface collapse of the medial femoral condyle (arrowhead in b and c), with depression of the subchondral bone plate (c) and loss of subchondral fatty signal intensity (b). The clinical scenario and histologic findings are typical of secondary osteonecrosis. Osteochondral lesions of the talus are common and difficult problems to treat. MRI features that aid in diagnosis include the location and extent of bone marrow edema, the presence of a fracture line, a hypointense area immediately subjacent to a subchondral bone plate, and a subtle or gross deformity of the bone plate. These osseous injuries are the result of impaction of the lateral femoral condyle against the posterolateral tibial plateau during internal rotation and anterior translation of the tibia accompanying an anterior cruciate ligament rupture (arrow in d). Cartilage is a connective tissue that covers the bones between joints. (c) Radiograph obtained 6 months later shows the progression of normal ossification (arrow). (b, c) Coronal T1-weighted (b) and proton-density–weighted fat-suppressed (c) MR images show a progeny (P) fragment separated from the parent bone, with signal intensity equal to that of fluid (white arrow in c) and an additional outer rim of sclerosis (black arrow in c). The risk of collapse in the femoral condyle seems to be related directly to the size and location of the infarct: Lesions involving more than one-third of the condyle on midcoronal MR images or the middle and posterior one-third of the condyle on midsagittal MR images are at higher risk of collapse (34). The cartilage can be torn, crushed or damaged and, in rare cases, a … This is essential in determining management. Inflammation: Your knee is inflamed. Based on Barrie and Laor et al (43,46). http://drroberlaprademd.com/ Colorado complex knee specialist Robert LaPrade MD, PhD. As demonstrated in studies of osteonecrosis of the femoral head (35), bone marrow edema distal to the infarct constitutes an indirect sign of articular collapse. MRI features of this lesion also have been shown to be profoundly different from those of primary AVN (17,18). Healing juvenile OCD in a 13-year-old boy. The laminar configuration of the signal intensity in the fragment reflects the presence of calcifications in its deep zone (arrow in b). 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