Etiology of Pain in Early Osteonecrosis of the Femoral Head
Abstract & Commentary
Synopsis: Serial MR images were used to correlate the course of marrow edema in the femoral head with hip pain prior to collapse. Edema correlated with pain; core decompression relieved pain through decreased marrow edema, and pain improvement generally paralleled resolution of edema.
Source: Koo KH, et al. Bone marrow edema and associated pain in early stage osteonecrosis of the femoral head: Prospective study with serial MR images. Radiology 1999; 213:715-722.
The subjects were patients participating in a trial for effectiveness of core decompression for early osteonecrosis of the femoral head. Thirty-three patients had MR imaging performed in the contralateral hips of patients with findings of osteonecrosis in one hip by radiograph, the hips of patients with hip symptoms without osteonecrosis seen radiographically, and osteonecrotic hips by radiography that did not show collapse. The femoral heads were studied by radiography, MR images, clinical evaluation, and bone scintigraphy. Patients were randomized after diagnosis to early core decompression or conservative treatment. The patients were followed at three-month intervals and evaluated for marrow edema around focal necrosis and joint effusion. Bone marrow pressure measurements and histopathologic findings were obtained in patients undergoing core decompression. Follow-up evaluation was continued until collapse of the femoral head was defined.
MR findings for marrow edema were signal abnormalities of low intensity on T1-weighted images and isointense or hyperintense on T2-weighted images involving the femoral head and neck beyond the necrotic zone and extending to the trochanteric area.
Seven (50%) of 14 symptomatic hips showed characteristic findings of marrow edema around focal osteonecrosis on MR images and one (4%) of 23 asymptomatic hips showed edema. Of seven hips that were moderately to severely painful, six (86%) were associated with surrounding edema. Only two (7%) of 30 hips with mild or no pain were associated with edema. Of these seven symptomatic femoral heads associated with edema, core decompression was performed in a randomly selected four. All showed relief of pain and edema within one week of surgery, while the remaining three remained symptomatic for months, then improved gradually.
Comment by Beverly P. Wood, MD
Pain is an important early symptom of osteonecrosis of the femoral head. Koo and colleagues have correlated pain with edema, but it is unlikely that edema is the cause of ischemia. Increased blood flow and capillary permeability are thought to produce the edema and are the result of the tissue ischemia. While core decompression results in rapid symptomatic improvement, there is no indication that this procedure alters the ultimate changes of osteonecrosis. The pain is transient and will resolve over time.
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