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Radiographs obtained 2 weeks after the onset of right hip pain. There were no significant findings on either the (A) anteroposterior view or the (B) frog lateral view.
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A plain radiograph of the right hip joint showed no signs in particular (Fig. 1), but there was a thick, very-low-signal-intensity band at the medial part of the femoral neck on T1-weighted and T2-weighted magnetic resonance images.
Coronal T1-weighted (A) and T2-weighted (B) magnetic resonance images show a thick low-signal-intensity band at the medial part of the femoral neck (white arrows). Furthermore, the irregular, serpentine, low-signal-intensity lesion extended and descended to the intertrochanteric area on T1-weighted images (black arrowheads). A coronal short tau inversion recovery sequence (C) shows an edema pattern in the bone marrow of the right femoral neck. A coronal gadolinium-enhanced T1-weighted magnetic resonance image (D) shows no contrast enhancement in the proximal segment from the distal low-intensity band. The proximal low-intensity band is not contrast-enhanced, but the distal low-intensity band is partially contrast-enhanced (white arrows).
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T1-weighted images (Fig. 2). The radiologist diagnosed occult fracture of the right femoral neck and osteonecrosis of the left femoral head on the basis of findings on plain radiographs and magnetic resonance images. ONFH caused the occult fracture (Fig. 2). On the basis of findings on all images, our diagnosis was occult fracture associated with extensive ONFH.
Bone scintigraphy images show increased radionuclide uptake in the medial part of the right femoral neck and decreased uptake in both femoral heads.
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Because the femoral head showed a cold uptake, bone scintigraphy raised the question of bilateral ONFH (Fig. 3).
Tomosynthesis (A) and computed tomography (B) images show a sclerotic lesion in the medial subcapital area (black arrows) that corresponds to the thick, low-signal intensity on T1-weighted and T2-weighted magnetic resonance images.
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Tomosynthesis and computed tomography were also performed on the right hip joint, and images from both processes showed a sclerotic linear lesion in the medial subcapital area (Fig. 4).
Photographs of the mid-coronal plane of the resected femoral head and neck, and the whole mounted histologic specimen (A). Microscopically, the trabecular bone and marrow in the femoral head are extensively necrotic (asterisk, area surrounded by black dotted line) (B). Red line and black arrows indicate the fracture line. A histopathologic image of the necrotic region shows accumulation of bone marrow cell debris, along with bone trabeculae with empty lacunae beneath the fracture line (C). The reactive zone is composed of vascular granulation tissue (solid arrowhead) and trabeculae thickened by the formation of appositional new bone (black arrows). The dotted line indicates the fracture line; the open arrowheads indicate necrotic trabeculae (D).
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Necrosis was extensive, as we expected, so the choice of bipolar hemiarthroplasty rather than osteosynthesis was correct (Fig. 5).