Anomalies of ossification in the posterolateral femoral condyle: assessment by MRI.
BACKGROUND
Anomalies of ossification in the lower femoral epiphysis are often radiographically indistinguishable from juvenile osteochondritis dissecans.


OBJECTIVE
To clarify the MRI characteristics of the anomalies of ossification in the posterolateral femoral condyle that distinguish it from juvenile osteochondritis dissecans.


METHODS
We retrospectively examined the medical records, plain radiographs (n = 4), MRI (n = 4) and follow-up MRI (n = 2) of four boys (age 8-11 years) with anomalies of ossification in the posterolateral femoral condyle.


RESULTS
Plain radiography showed symmetrical marginal irregularity of the posterolateral femoral condyles of both knees. These lesions were asymptomatic, and the areas of irregular radiographic appearances reduced in size or disappeared without treatment within a mean observation period of 3.5 months. MRI showed a clearly demarcated low-intensity islet with the same signal intensity as subchondral bone (which was considered to be an accessory ossification nucleus) in a high-signal area in which the signal intensity was equal to that of normal articular cartilage. The areas observed as radiolucent zones on plain radiography were visualised at the same signal intensity as articular cartilage, and were continuous with articular cartilage on MRI; thus they were regarded as uncalcified cartilage. These MR findings are different from MR images of osteochondritis dissecans.


CONCLUSIONS
MRI is considered to be the most effective non-invasive diagnostic method for these two conditions.
Nawata
K
K
Department of Orthopaedic Surgery, Faculty of Medicine, Tottori University, 36-1 Nishimachi, Yonago 683-8504, Japan.
Teshima
R
R
Morio
Y
Y
Hagino
H
H
D002648:Child; D003937:Diagnosis, Differential; D004838:Epiphyses / Q000000981:diagnostic imaging / Q000473:pathology; D005269:Femur / Q000000981:diagnostic imaging / Q000473:pathology*; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000473:pathology*; D008279:Magnetic Resonance Imaging; D008297:Male; D009999:Ossification, Heterotopic / Q000175:diagnosis*; D010008:Osteochondritis Dissecans / Q000175:diagnosis*; D011859:Radiography; D012189:Retrospective Studies