Osteochondral Lesions of the Knee: Differentiating the Most Common Entities at MRI

Abstract

Several pathologic conditions may manifest as an osteochondral lesion of the knee that consists of a localized abnormality involving subchondral marrow, subchondral bone, and articular cartilage. Although understanding of these conditions has evolved substantially with the use of high-spatial-resolution MRI and histologic correlation, it is impeded by inconsistent terminology and ambiguous abbreviations. 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. Patient demographics, the clinical presentation, and the role of trauma are critical for differential diagnosis. A localized osteochondral defect can be created acutely or can develop as an end result of several chronic conditions. 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 the subchondral bone plate, and deformity of the subchondral bone plate. These findings are essential in diagnosis of acute traumatic injuries, subchondral insufficiency fracture, and its potentially irreversible form, spontaneous osteonecrosis of the knee. 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. 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. Once the diagnosis is established, it is important to report pertinent MRI findings that may guide treatment of each condition. RSNA, 2018 An earlier incorrect version of this article appeared online. This article was corrected on August 23, 2018.

Corticosteroid-induced Knee Osteonecrosis and Accompanying Femoral Head Osteonecrosis

“…A circumscribed subchondral "band-like" hypointense lesion on T1W images and "double-line sign" on T2W images were considered pathognomonic for femoral head ON (22). The "double-line sign" consists of a hypointense outer rim (represents the reactive bone) and a hyperintense inner rim (represents granulation tissue) on T2W images.…”

Edema-like marrow signal intensity: a narrative review with a pictorial essay

“…This area, representing local ischemia, is very important because if it is thicker than 4 mm or longer than 14 mm, the lesion may be irreversible and may evolve into irreparable epiphyseal collapse and articular destruction. For this reason, this area acts as the most important prognostic indicator of more rapidly progressive lesion [65,66]. Unfortunately, ELMSI does not appear to have a prognostic role in prediction of poor clinical outcome because diffuse marrow changes can be observed in the early stages of irreversible osteonecrosis and in transient lesions as well.…”

Perspective on Idiopathic Subchondral, Osteochondral, and Chondral Lesions with Emphasis on the Knee

“…Fluid-filled fracture lines or depression of the joint surface demonstrate rather advanced findings indicating structural instability of an osteochondral fragment. 50 As an earlier sign of an unfavorable outcome, a lowsignal area adjacent to the subchondral bone plate was described, representing a combination of callus formation and secondary osteonecrosis. 50 According to the study published in 1998 by Lecouvet and colleagues, 24 it is always stated that such a low-signal area indicates irreversible necrosis if it is thicker than 4 mm and longer than 14 mm (►Fig.…”

“…In contrast to traumatic osteochondral lesions, OCD initially occurs in the subchondral bone and involves the articular cartilage secondarily. 50 In the knee, OCD is usually divided into a juvenile and an adult form. The juvenile OCD occurs before the closure of the growth plates.…”