MR appearance of SONK-like subchondral abnormalities in the adult knee: SONK redefined.
OBJECTIVE
To investigate the MR characteristics of SONK-like (spontaneous osteonecrosis of the knee) subchondral abnormalities in the adult atraumatic knee and to recategorize these patients into two subgroups: a subacute to chronic process associated with osteoarthritis and an acute process associated with insufficiency fractures.


METHODS
We retrospectively examined the knee MRIs of 39 patients with non-specific interpretations of osteochondral abnormalities.


METHODS
There were a total of 52 subchondral lesions without any known traumatic event and no prior surgery. All lesions evaluated had MR features previously ascribed to SONK. Several MR characteristics were then assessed: presence or absence of a line, size, zonal location, T1 and T2 signal, associated marrow edema, associated ipsilateral meniscal tear, and associated ipsilateral cartilage defects.


CONCLUSIONS
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.
Ramnath
R Richard
RR
Massachusetts General Hospital, Harvard Medical School, 55 Fruit Street, ACC 515, Boston, MA 02114, USA.
Kattapuram
Susan V
SV
D000208:Acute Disease; D000328:Adult; D000368:Aged; D001855:Bone Marrow Diseases / Q000473:pathology; D002357:Cartilage Diseases / Q000473:pathology; D002908:Chronic Disease; D004487:Edema / Q000473:pathology; D005260:Female; D005598:Fractures, Spontaneous / Q000473:pathology; D006801:Humans; D007718:Knee Injuries / Q000473:pathology; D007719:Knee Joint / Q000473:pathology*; D008279:Magnetic Resonance Imaging; D008297:Male; D008592:Menisci, Tibial / Q000473:pathology; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000473:pathology; D010020:Osteonecrosis / Q000473:pathology*; D012189:Retrospective Studies; D012422:Rupture, Spontaneous