PMC4066577_01
A supine anteroposterior radiograph obtained 1 month after the onset of pain in the right hip shows acetabular dysplasia, the lytic area in the superolateral portion of the femoral head and slight joint-space narrowing.
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Initial radiographs obtained 1 month after pain onset revealed mild acetabular dysplasia [center-edge angle, 15 ; inclination angle of the weight-bearing portion of the acetabulum, 13 ] and joint-space narrowing in the weight-bearing area (Fig. 1).
Images obtained 2 months after the onset of hip pain: (A) radiograph showing no remarkable changes in the joint space. (B) Computed tomography multiplanar reconstruction showing a lytic lesion with a well-defined sclerotic margin in the superolateral portion of the femoral head. (C) Coronal T1-weighted magnetic resonance image showing diffuse low signal intensity in the superolateral portion of the femoral head and acetabular rim. (D) Corresponding area of high signal intensity on the short tau inversion recovery (STIR) sequence. On the femoral side, there is a very high signal intensity area on the STIR sequence as well. A well-delineated round, low-intensity band is also visible on the T1-weighted image and the STIR sequence.
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At 2 months after the onset of hip pain, radiographs showed no significant changes since the initial radiographs (Fig. 2A). Computed tomography (CT) showed a cystlike formation in the superolateral portion of the femoral head, facing the acetabular rim (Fig. 2B). T1-weight images and a very high signal intensity on the short tau inversion recovery (STIR) sequence of the superolateral portion of the femoral head, which was surrounded by a pattern of edema in the bone marrow. The edema pattern was found not only in the femoral head but also in the acetabulum facing the cystic lesion on the femoral head (Fig. 2C, D).
Images obtained 3 months after the onset of hip pain. (A) Radiograph showing that the joint space had been maintained. Magnetic resonance images (B, T1-weighted; C, short tau inversion recovery sequence) showing that the marrow edema pattern in the bone marrow had slightly lessened.
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Interestingly, although radiographs obtained just before surgery showed no remarkable changes (Fig. 3A), MRI performed at the same time showed that the edema pattern had been slightly alleviated compared with 1 month earlier (Fig. 3B, C).
A supine anteroposterior radiograph obtained immediately after total hip arthroplasty.
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Three months after the onset of hip pain, we performed a total hip arthroplasty for the patient because of her persistent pain (Fig. 4).
(A) During surgery, the anterosuperior labrum was found to be inverted into the articular space (arrowheads). (B) After resection of the inverted labrum (asterisk) and (C) resection of the femoral head, it was apparent that only the area of the articular cartilage in contact with the inverted labrum was damaged (arrows). (D) Illustration indicating how the inverted labrum affect articular cartilage and subchondral bone.
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During surgery, we found an inverted labrum (Fig. 5A) with degenerative changes in the acetabular cartilage just beneath it (Fig. 5B). Similarly, there were degenerative changes of the femoral head cartilage on the superolateral portion, which corresponded to the area of the inverted labrum (Fig. 5C).
(A) A midcoronal cross-section of the resected femoral head shows a whitish round area (arrowheads) beneath the articular cartilage. (B, C) Photomicrographs obtained from the subchondral area shown in Fig. A outlined by black arrowheads demonstrates a fracture callus and granulation tissue (hematoxylin and eosin staining). (D) A photograph of the resected inverted labrum and (E) its photomicrograph show that the free end of the inverted labrum is severely fibrillated because of abrasion, but detritic changes are not remarkable.
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A midcoronal cross-section showed a round, whitish gray mass of tissue under the cartilage (Fig. 6A). Microscopically, the whitish gray region consisted of fracture callus and granulation tissue (Fig. 6B), which corresponded to the round, low-intensity area on T1-weighted magnetic resonance images. SIF. Surprisingly, subchondral bone just beneath the articular cartilage was intact despite the breakage of slightly distal trabeculae (Fig. 6B).