MR appearance of SONK-like subchondral abnormalities in the adult knee: SONK redefined

Abstract

The abnormalities with linear components (insufficiency fractures) tended to be larger (P<0.01) and were associated with a severe amount of marrow edema (P<0.0001) consistent with an acute process. The non-linear abnormalities were more associated with cartilage defects (P=0.01) and less marrow edema consistent with osteoarthritis and a subacute to chronic process. This association of SONK-like abnormalities with osteoarthritis and insufficiency fractures casts doubt on the validity of the term "spontaneous osteonecrosis" as it is currently applied, and further investigation into the separate etiologies of these subchondral marrow lesions is needed.

Femoral condyle insufficiency fractures: associated clinical and morphological findings and impact on outcome

“…In particular, adjacent cartilage loss and cartilage WORMS score were significantly higher among the progression group, with overlying cartilage loss also showing a mild association with progression as well. The intimate ties between cartilage health and FCIF have previously been described [6]. Though our study does not establish causality in this relationship between cartilage integrity and lesion progression, it does raise the possibility that FCIF lesions may give rise to more rapid cartilage destruction, as is sometimes seen with similar lesions of the femoral head [33,34].…”

“…Location was described according to a zone system detailed by Ramnath and Kattapuram, which is outlined in Fig. 3 [6]. Involvement of the weight-bearing versus nonweight-bearing condyle surface was noted.…”

“…In 1999, Yamamoto et al described subchondral insufficiency fractures of the femoral head within lesions previously classified as osteonecrosis [4]. This discovery prompted a reevaluation of SONK at the femoral condyle [2,5,6]. A spectrum of femoral condylar pathology has since been proposed, with FCIF and osteonecrosis being recognized as distinct entities along this spectrum, and osteoporosis was implicated as a risk factor [2,[7][8][9][10].…”

MR Imaging of Epiphyseal Lesions of the Knee: Current Concepts, Challenges, and Controversies

“…The consistent observation is a low signal intensity line running almost parallel to the subchondral bone plate at a variable distance from the epiphyseal surface, representing the fracture plane, and surrounded by BME (Figs. 6 and 7) [48,52,57]. This appearance parallels that of occult posttraumatic fractures [100 -102].…”

“…Accumulation of these microfractures with failure of repair mechanisms could induce subchondral bone destruction, which may eventually lead to subchondral bone plate collapse typical for epiphyseal osteonecrosis. Clinical findings, MR imaging, and histology support this hypothesis of the role of a subchondral bone fracture as initiating lesion (Box 1) [17,49,57]. The most important clinical factors that promote this hypothesis are the abrupt onset of symptoms, the specific patient population, the absence of systemic risk factor, and the lesion location (Box 1).…”