To the Editor:
We read with great interest thr article by Cheng et
al.(1). We agree with the authors that early and asymptomatic
osteonecrosis has a possibility of spontaneous resolution and have reported spontaneous resolution in large necrotic
lesions which impinged on two-thirds or more of the weight
bearing portion of the acetabulum (2). We reported that the initial
MR abnormalities indicating oseonecrosis were seen between 2 and
4 months after the initiation of steroid therapy(2).
In the
article by Cheng, et al(1), the interval between the transplantation and the initial diagnosis of
osteonecrosis was between four and seven months. We speculate that spontaneous resolution in the authors' cases had
already begun at the time of their initial diagnosis and that the initial sizes of
the necrotic lesions might have been larger before they were detected by the authors.
Large necrotic lesions have been reported to tend to
collapse and spontaneous resolution may not develop after
collapse. Subchondral fracture in the necrotic area leads to
abnormal distribution of weight-bearing forces, and altered weight-
bearing may cause abnormal mechanical stress on the demarcated
zone and surrounding healthy bone(3).
Even if necrotic lesions
are large, they have the potential to resolve spontaneously,
so long as there is a normal mechanical distribution of
weght-bearing forces, but subchondral fractures can develop in
association with minor trauma. We think that for the prevention
of collapse, it is important to advise patients with these lesions not to do strenuous
activities.
References:
1.Edward Y. Cheng, Issada Thongtrangan, Alan Laorr, and Khaled J. Saleh
Spontaneous Resolution of Osteonecrosis of the Femoral Head
J Bone Joint Surg Am 2004; 86: 2594-2599
2. Sakamoto M, Shimizu K, Iida S, Akita T, Moriya H, Nawata Y.
Osteonecrosis of the femoral head(a prospective study with MRI). J Bone
joint Surg Br, 1997;79:213-219.
3. Iida S, Harada Y, Shimizu K, Sakamoto M, Ikenoue S, Akita T,
Kitahara H, Moriya H. Correlation between bone marrow edema and collapse
of the femoral head in steroid-induced osteonecrosis. AJR, 2000;174:735-
743.
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