Because of the proven microtraumatic origin of SONK and the histopathologic and MRI features that unite it with SIF, it is currently accepted that a SONK is a SIF that has progressed into collapse, with secondary necrosis found in the collapsed specimens. Although the articular surface and subchondral bone plate are intact, the presence of bone marrow edema surrounding the AVN (white *) suggests an impending articular collapse. OCD is a focal idiopathic alteration of subchondral bone with a risk for instability and disruption of adjacent articular cartilage that may result in premature osteoarthritis (39,40). A fluid-filled break in the articular surface (arrowhead) is present, and there is fluid at the anterior interface of the fragment (arrow). 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). Figure 17b. Classic SIF in a 64-year-old man. See osteochondritis dissecans article for a general discussion. Diagram of image from a fluid-sensitive sequence (a), coronal T1-weighted MR image (b), and proton-density–weighted fat-suppressed MR image (c) show multiple regions of AVN in the femur and tibia. Figure 13. Several factors are responsible for development of a collapse that signifies failure of the subchondral bone plate: (a) the cumulative effect of fatigue microfractures in the necrotic zone, (b) osteoclastic activity that causes weakening of the trabeculae in the reparative front, and (c) focal concentration of mechanical stress on thickened bone trabeculae of the reparative zone along the AVN margins that act as “stress risers” (31–33). Focal discontinuity of the subchondral bone plate is seen (arrowhead). In early uncomplicated AVN, the marrow signal in the infarct is preserved, representing mummified fat, and there is no surrounding bone marrow edema. More important are the localized abnormalities in the subchondral region, best shown on T2-weighted and proton-density–weighted MR images. A bone contusion (* in b) is visible at the posterior aspect of the lateral tibial plateau. Histologic core biopsy specimens obtained in juvenile OCD lesions showed that osteonecrosis is either absent (47,50) or infrequent (48,51). Osteochondral injury is commonly associated with immediate effusion that represents hemarthrosis or lipohemarthrosis. Anterior femoral condylar fracture and bone contusion at the anterior aspect of the tibia (* in b) are the results of an internal force that occurred during hyperextension as the femur and tibia collide. what's wrong with my knee? A bone contusion (* in b) is visible at the posterior aspect of the lateral tibial plateau. Focal discontinuity of the subchondral bone plate is seen (arrowhead). Figure 5c. The distal femoral growth plate is open (* in a and b). Figure 17a. AVN of the medial femoral condyle in a 29-year-old woman with lupus. Figure 11a. Diagram (a), coronal proton-density–weighted fat-suppressed MR image (b), and sagittal T2-weighted fat-suppressed image (c) show a bone marrow edema pattern “painting” the entire medial femoral condyle (* in b). The highly organized collagen network in the cartilage displays T2 anisotropy, and the regional variations in cartilage signal intensity are affected by the “magic angle” effect (3) (Fig 2). Figure 5a. Figure 11b. (a) Diagram shows a fracture that is creating an osteochondral fragment. OCD is a focal idiopathic alteration of subchondral bone with a risk for instability and disruption of adjacent articular cartilage that may result in premature osteoarthritis (39,40). It can manifest clinically with vague pain, or there may be no symptoms until development of subchondral bone plate fracture, (ie, collapse). The laminar configuration of the signal intensity in the fragment reflects the presence of calcifications in its deep zone (arrow in b). Note the lack of edema in the necrotic segment. An osteochondral lesion is a defect in the cartilage of a joint and the bone underneath. The distal femoral physis is closed (*). Enter your email address below and we will send you the reset instructions. Figure 10c. 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. Osteochondral fracture with a subchondral bone plate depression in an 18-year-old man. (d) MR image obtained 6 months later shows restoration of the subchondral bone plate (arrowhead). Figure 18b. MRI appearance of the osteochondral junction. 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). OCD in the extended classic location in a 19-year-old man, with features of instability applicable to both juvenile and adult OCD. (a) Initially, a large area of necrosis shows normal marrow signal intensity that represents mummified fat (black *) outlined with a sclerotic rim (arrows) that is convex to the articular surface. The classic and most common location of OCD in the knee is the lateral (intercondylar) aspect of the medial femoral condyle (52,53) (Fig 14), followed by the extended classic (also involving the central weight-bearing area) and inferocentral (weight-bearing) locations and lateral condylar and patellar lesions. Coronal proton-density–weighted fat-suppressed MR image (a) sagittal proton-density–weighted MR image (b), and T2-weighted fat-suppressed MR image (c) show an OCD lesion in a classic location at the lateral aspect of the medial femoral condyle with cysts (curved arrow in a and c) and a high-signal-intensity rim (straight arrow in b) at the interface between the fragment and parent bone associated with breaks in the subchondral bone plate and articular cartilage along the periphery of the lesion (arrowhead in b and c). An osteochondral defect can be created acutely or, more often, develops as a common final pathway of several chronic conditions. Healing juvenile OCD in a 13-year-old boy. They typically are associated with a history of trauma; however, nontraumatic etiologies have been described. Such lesions are a tear or fracture in the cartilage covering one of the bones in a joint. When analyzing osteochondral lesions on MR images of the knee, the radiologist must first consider patient demographics, clinical presentation, and history of trauma. SIF in a 64-year-old woman with a complex tear in the medial meniscus with peripheral extrusion (arrow in a). Note the peripheral extrusion of the medial meniscus (black arrow in b) from a posterior horn tear (not shown). Unlike the appearance in primary osteonecrosis, the line is incomplete, and edema appears on both sides of the line. It may be less conspicuous on T2-weighted images when it is hyperintense and surrounded by bone marrow edema, unless there is a component of trabecular impaction that renders the fracture hypointense on both T1- and T2-weighted MR images, similar to the appearance of stress fractures. The deepest calcified cartilage layer is located at the interface with the subchondral bone plate, a layer of compact cortical bone that overlies the cancellous marrow-containing trabecular bone. (c) Radiograph obtained 6 months later shows the progression of normal ossification (arrow). This is essential in determining management. Material and Methods: We retrospectively evaluated MR imaging findings of all knee MRI exams performed at our institution over the past five years. Figure 18b. Subchondral fracture in a 32-year-old man with an acute medial collateral ligament tear (arrow in d) and an anterior cruciate ligament rupture (not shown). Figure 9b. ance of the lesion over 4 years (Fig. T1 Figure 17c. Figure 18a. Figure 10a. Figure 19b. AVN of the knee in a 59-year-old woman who was undergoing long-term corticosteroid treatment. (b) Coronal proton-density–weighted fat-suppressed MR image shows an OCD lesion surrounded by a rim of increased signal intensity (thick arrow) that is not as intense as the joint fluid (thin arrow). Instead, they are fluid-filled lesions surrounded by bone. Figure 8a. The unique feature of this condition is that separation and detachment of the osteochondral fragment culminate the process that originally starts deep underneath the articular surface (43) and subsequently involves the articular cartilage at the peripheral border of the lesion: an “inside-out” mechanism. The MRI appearance of individual layers depends on both anatomic and technical factors. Typical patient demographics and clinical presentation, the etiologic role of trauma, and classic MRI features that help to guide appropriate treatment are described for each entity (Table). SIF in a 51-year-old woman with atraumatic sudden onset of knee pain and swelling. The suffix “-like” is used because of a large spectrum of histologic changes responsible for these patterns of signal intensity alteration on MR images. An unstable fragment may be unsalvageable when it consists of cartilage only (no bone on the deep surface), is composed of multiple pieces, or contains damaged or absent articular cartilage (58). 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). The cartilage can be torn, crushed or damaged and, in rare cases, a … Figure 10a. A bone contusion (* in b) at the lateral tibial plateau can be distinguished from a fracture because of the absence of a contour deformity or fracture line. Diagram shows the classic four signs of instability in an OCD lesion: 1, high signal intensity rim at the interface between the fragment and the adjacent bone on T2-weighted MR images; 2, fluid-filled cysts beneath the lesion; 3, a high-signal-intensity line extending through the articular cartilage overlying the lesion; and 4, a focal osteochondral defect filled with joint fluid. Coronal proton-density–weighted fat-suppressed (a) and sagittal T2-weighted (b) MR images show articular surface collapse with a depression of the subchondral bone plate (arrowhead in a) and a fluid-filled fracture cleft underlying the subchondral bone plate (arrow). (b) Subsequently, a frank articular collapse (arrowheads) has developed, followed by loss of fatty signal intensity in the necrotic area (arrows). Figure 11c. SIFs are associated with meniscal tears in the same compartment in 76%–94% of patients (18,20,21). Diagram of the fluid-sensitive MR image (a) and sagittal T2-weighted fat-suppressed (b), coronal T1-weighted (c), and proton-density–weighted fat-suppressed (d) MR images show a subchondral fracture (arrow in b and c) as a curvilinear hypointensity surrounded by bone marrow edema, without associated contour deformity. (b) Coronal proton-density–weighted fat-suppressed MR image shows an OCD lesion surrounded by a rim of increased signal intensity (thick arrow) that is not as intense as the joint fluid (thin arrow). The actual defect may or may not be present on MR images, depending on the stage of the process. With regard to true primary osteonecrosis of the knee, general imaging principles of primary osteonecrosis can be applied, and some features established in studies of AVN of the hip can be extrapolated (19,29). If the lesion consists of a subchondral region demarcated from the surrounding bone, the demarcation should be examined for completeness and the presence of a “double-line sign” that is seen in avascular necrosis or findings of instability, which are important for proper evaluation of osteochondritis dissecans. The diagnosis was a collapsed SIF with secondary osteonecrosis (SONK). (a) Diagram shows a fracture that is creating an osteochondral fragment. The compact subchondral bone and calcified cartilage are collectively termed the subchondral plate (4,5). Osteoarthritis in a 50-year-old woman. These findings are essential in diagnosis of acute traumatic injuries, subchondral insufficiency fracture, and its potentially irreversible form, spontaneous osteonecrosis of the knee. Healing juvenile OCD in a 13-year-old boy. ■ Contrast and compare common entities that manifest as osteochondral lesions of the knee: acute traumatic osteochondral injuries, AVN, SIF of the knee, OCD, bone marrow edema-like lesions, and subchondral cystlike lesions in osteoarthritis. For this journal-based SA-CME activity, the authors, editor, and reviewers have disclosed no relevant relationships. Figure 17c. (d) Sagittal T2-weighted fat-saturated MR image shows disruption of the subchondral bone plate (arrowhead). Edema is present in the bed of the defect (asterisk). While osteonecrosis can be idiopathic, common causes of osteonecrosis include trauma, use of corticosteroids, sickle cell anemia, collagen vascular disease, and alcoholism (28). In addition to osteoarthritis, subchondral cystlike lesions may be prominent in rheumatoid arthritis and calcium pyrophosphate deposition disease (67). This pattern of bone injury should prompt a search for additional findings of hyperextension with a varus or valgus component. Sagittal proton-density–weighted (a) and T2-weighted fat-suppressed (b) MR images of the medial femoral condyle show subchondral cystlike lesions (arrow) and bone marrow edema-like lesions (* in b). Osteochondral fracture with a subchondral bone plate depression in an 18-year-old man. Figure 1. 3, © 2020 Radiological Society of North America, Evaluation and management of osteochondral lesions of the talus, Acute and stress-related injuries of bone and cartilage: pertinent anatomy, basic biomechanics, and imaging perspective, In vitro MR imaging of hyaline cartilage: correlation with scanning electron microscopy, The tibial subchondral plate. Diagram (a), coronal proton-density–weighted fat-suppressed MR image (b), and sagittal T2-weighted fat-suppressed image (c) show a bone marrow edema pattern “painting” the entire medial femoral condyle (* in b). Subchondral fracture in a 32-year-old man with an acute medial collateral ligament tear (arrow in d) and an anterior cruciate ligament rupture (not shown). AVN of the knee in a 59-year-old woman who was undergoing long-term corticosteroid treatment. OCD in the extended classic location in a 19-year-old man, with features of instability applicable to both juvenile and adult OCD. These two patterns may coexist. However, the bone marrow edema-like pattern is typically localized in osteoarthritis and extensive in SIF; articular cartilage may be preserved in early SIF, while significant cartilage loss typically accompanies eburnation in osteoarthritis. The laminar configuration of the signal intensity in the fragment reflects the presence of calcifications in its deep zone (arrow in b). Figure 14a. Figure 16a. MRI features of this lesion also have been shown to be profoundly different from those of primary AVN (17,18). A study by Yamamoto and Bullough (15), which was supported by results of a later study (16), showed that the primary event is a SIF, followed by secondary necrosis limited to the area between the fracture line and the subchondral bone plate. We have recog-nized the appearance of such lesions in the hip and report on their MR imaging appearance and occurrence in elite athletes. Advanced SIF in a 69-year-old woman with several months of unrelenting knee pain after walking down stairs. An earlier incorrect version of this article appeared online. Osteochondritis dissecans (OCD) most commonly affects the knee. (c) Radiograph obtained 6 months later shows the progression of normal ossification (arrow). Figure 16b. Art. Osteochondral fracture in a 32-year-old man with a hyperextension injury associated with a posterior cruciate ligament tear (not shown). †See text for description of specific features. 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