We investigated early osteonecrosis using in vivo magnetic 1 resonance imag
ing in a nontraumatic rabbit model of serum-sickness osteonecrosis in which
osteonecrosis was induced after two intravenous injections of horse serum
with a 3-week interval. One week (group A, 17 rabbits) and 3 weeks (group B
, 13 rabbits) after the second serum injection, coronal magnetic resonance
images of the femur were obtained and it was removed for histological study
. Some of the necrotic lesions in the diaphysis were detected on T1-weighte
d, T2-weighted, or fat-suppression T1-weighted images (six of 24 necrotic l
esions in group A and 16 of 18 in group B), and all of the necrotic lesions
in the epiphysis, metaphysis, and diaphysis were detected on T1-weighted o
r fat-suppression T1-weighted images enhanced with gadolinium-diethylene tr
iamine pentaacetic acid. All focal homogeneous enhanced areas on T1-weighte
d or fat suppression T1-weighted images corresponded to necrotic lesions (2
2 of 24 necrotic lesions in group A and 18 of 18 in group B); the contours
of the enhanced areas were displayed more clearly on the fat-suppression T1
-weighted than on the T1-weighted images. The fat-suppression T1-weighted i
mage enhanced with gadolinium-diethylene triamine pentaacetic acid was thus
the most sensitive and specific of five kinds of magnetic resonance images
for the detection of early necrotic lesions. The results suggest that this
image may be useful for early diagnosis of clinical osteonecrosis and for
obtaining information about the pathomechanism of osteonecrosis.