Hip Pain in a 24-year-old Woman

HISTORY AND PHYSICAL EXAMINATION A 24-year-old woman was admitted complaining of pain in the right hip and limp for 3 years. Her pain was initially intermittent, dull and aching in nature, aggravated on walking and relieved by nonsteroidal antiinflammatory drugs. One month before admission, her pain became continuous, especially worse at night. She had no clear history of trauma or constitutional symptoms. There was no past history of steroid intake, chronic disease, previous surgery, or addiction. On physical examination, she had fullness and tenderness in Scarpa's triangle. She had a fixed flexion deformity of 20° and further flexion to 110° in the right hip. She had internal rotation to 0°, external rotation to 30°, abduction to 15°, and adduction to 10°. There was 7-mm shortening of the affected leg. Examination of the spine, contralateral hip, and ipsilateral knee revealed no abnormality. There was no distal neurovascular deficit. Laboratory investigations, including total and differential leukocyte counts, erythrocyte sedimentation rate, and Creactive protein, were normal. Plain radiographs of the pelvis (Fig 1), lateral radiograph of the right hip (Fig 1), magnetic resonance imaging (MRI) (Fig 2), and bone scan (Fig 3) were done. Based on the history, clinical examination, laboratory investigations, and imaging studies, what is the differential diagnosis?Fig 1A: B. (A) An anteroposterior radiograph of the hip shows mixed lytic and sclerotic lesions in the femoral head. Note collapse of the superior margin of the femoral head. (B) A lateral radiograph of hip shows cystic lesions.Fig 2A: D. (A) T1-weighted coronal and (C) T1-weighted axial images show a low signal intensity lesion in the bone marrow of the right femoral head, surrounded by a signal void rim, with surrounding joint effusion. (B) T2-weighted coronal and (D) T2-weighted axial images show a lesion with mixed low and high signal intensities surrounded by a signal void rim. Bone marrow edema and joint effusion are seen on these images.Fig 3A: D. Bone scans show increased uptake of radioisotope in the right femoral head on (A) anteroposterior and (C) lateral projections as compared to the left femoral head (B and D).IMAGING INTERPRETATION A plain anteroposterior radiograph of the pelvis showed mixed lytic and sclerotic change of the femoral head with collapse of the superior weightbearing portion of the right femoral head (Fig 1A). On the lateral view, the sphericity of the femoral head was well maintained (Fig 1B). MRI, showed a multiloculated lesion, which was low on T1-weighted images (Figs 2A, 2C) and heterogeneous on T2-weighted images with areas of signal hyperintensity (Figs 2B, 2D). A low signal intensity rim was noted on all sequences. There was collapse of the superior weightbearing portion of the femoral head on MRI. Edema in the surrounding bone marrow and joint effusion were seen on all images (Fig 2). There was no periosteal reaction on radiographs or MRI. Bone scan showed uniformly increased uptake in the right femoral head (Fig 3). DIFFERENTIAL DIAGNOSIS Osteonecrosis Chondroblastoma Giant cell tumor Enchondroma Chondromyxoid fibroma Chronic granulomatous infection Our presumptive diagnosis, based on clinical and radiographic findings, was osteonecrosis. We thought simple curettage and bone grafting might not be effective for preservation of the femoral head, particularly in the presence of collapse of the superior weightbearing portion. Therefore we planned muscle-pedicle bone grafting. The curettings were atypical for osteonecrosis, so we requested a frozen-section biopsy (Figs 4, 5). Based on the history, clinical examination, laboratory investigations, imaging studies, and histology, what is the diagnosis and how should this lesion be treated?Fig 4: A photomicrograph of the lesion shows proliferation of chondroblasts with hyperlobulated nuclei and scanty basophilic cytoplasm. Multinucleated giant cells and chondroid material are also seen (Stain, hematoxylin and eosin; original magnification, ×100).Fig 5: A magnified photomicrograph shows the cytologic characteristics of the lesion (Stain hematoxylin and eosin, magnification ×400).See page 266 for diagnosis and treatment. Continuation of ORP conference from page 264. HISTOLOGY INTERPRETATION The curetting showed soft, friable granulation tissue with grayish white cartilaginous fragments. The histopathologic examination showed sheets of compact polyhedral chondroblasts with well-defined cytoplasmic borders, scanty amounts of basophilic cytoplasm, and nuclei that were hyperlobulated with longitudinal grooves. Multinucleated giant cells and foci of chondroid matrix were also seen. These findings suggested chondroblastoma1,6 (Figs 4, 5). DIAGNOSIS Chondroblastoma of the femoral head DISCUSSION AND TREATMENT Chondroblastoma of bone is a rare benign bone tumor, arising from the secondary centers of ossifications of long bones during the second decade of life.2,12,17,20 The histopathologic description of chondroblastoma according to the World Health Organization is “a relatively benign tumor, characterized by highly cellular and relatively undifferentiated tissue, made up of rounded or polygonal chondroblast-like cells with distinct outlines and multinucleated giant cells of osteoclast type arranged singly or in groups. The presence of cartilaginous intercellular matrix with areas of focal calcification is typical.”4 A few large series have been reported and the common location described is the proximal femur,2,17 proximal humerus,12,20,23 and proximal tibia.15,25 In this case, it was difficult to confirm the diagnosis based on radiographic imaging alone. The earliest radiographic sign of osteonecrosis is a radiolucent crescent, which can be seen as early as 4 weeks. In its advanced stages, osteonecrosis can be readily identified radiographically by a mottled osteolytic and sclerotic subchondral lesion surrounded by a distinct sclerotic rim with or without flattening of the articular surface.10 On MRI, the subchondral necrotic defect shows different signal alterations (Classes A to D, according to Mitchell and associates7). These signal changes are surrounded by a band of low signal intensity on T1-weighted images. On T2-weighted images, a second inner rim of high signal has been observed (the double line sign), which is believed to represent fibrovascular tissue in the reparative zone. Bone scans are highly sensitive for the diagnosis of early osteonecrosis changes, but their specificity is low and the findings can reflect other conditions.11 The interruption of the blood supply, detected as a cold spot, is a nonspecific pattern and can be found in several other bone marrow processes. The repair process, seen as a hot spot, is the most common finding in osteonecrosis but is nonspecific. Only the combination of a cold spot in a hot spot represents a diagnostic pattern for osteonecrosis. In one reported series,11 a nonspecific hot spot was found in 58% of lesions and the characteristic hot in cold pattern in only 13%. Characteristic radiographic features of a benign tumor are geographic bone destruction, sclerotic margin, solid periosteal reaction or no periosteal reaction, and no soft tissue mass. Cartilaginous tumors are characterized by lobulation (endosteal scalloping) and punctate, annular, or commalike calcifications in the matrix.8 On MRI, the presence of 2- to 5-mm-diameter lobules of cartilage with or without calcification and/or ossification is relatively specific for well-differentiated cartilage matrix tumors.26 Diagnostic radiographic features of chondroblastoma include a lytic lesion surrounded by sclerotic border, usually located eccentrically in a growing bone. Scattered calcification of matrix is seen in 25% of lesions and thick solid periosteal reaction distal to the lesion is seen in 57% of them.8 Calcification is demonstrated better on computed tomography (CT) scan. MRI usually shows a larger area of involvement than that seen on radiographs; the calcification is seen as a well-defined area of low to intermediate signal intensity on T1-weighted images and a heterogeneous area of increased signal intensity in a noncalcified chondroid matrix on T2-weighted images.5 T2-weighted images also show lobular internal architecture and fine lobular margins of the lesion. Bone marrow and soft tissue edema, diaphyseal periosteal reaction, and joint effusion are also common findings.21 Giant cell tumor presents as a radiolucent lesion, almost always localized to the articular end of the bone. Calcification found on CT will essentially exclude giant cell tumor.26 Enchondroma is less common in long tubular bone and is rarely epiphyseal. It has the characteristic radiographic and MRI appearance of a benign cartilage tumor but is usually not associated with marrow edema or periosteal reaction. The upper femoral epiphyseal region is also an uncommon location for chondromyxoid fibroma, which clinically presents with local swelling and pain. The characteristic radiographic picture is that of an eccentrically located radiolucent lesion in the bone, with a sclerotic scalloped margin, often eroding or ballooning out the cortex. Calcification is not apparent radiographically, but focal microscopic calcification may be seen.8 Chronic granulomatous infection is virtually ruled out in the presence of normal laboratory findings. The characteristic radiographic findings of tuberculous infection include the triad of periarticular osteoporosis, peripherally located osseous erosions, and gradual diminution of the joint space.9 Chronic granulomatous fungal infections like coccidioidomycosis are usually characterized by well-marginated, punched out osteolytic lesions, typically unilocular with occasional periosteal reaction. Soft tissue swelling and osteoporosis are more common.9 They may sometimes be associated with bone marrow edema, but the lobular pattern of foci of low, intermediate, and high signal intensity seen within the lesion on T2-weighted images is not known to occur in chronic infections. The presentation of chondroblastoma in this case is atypical in several ways. First, chondroblastoma typically occurs in the second decade of life and is more common in men. Our patient was a 24- year-old woman. Second, she presented with pain in the right hip of relatively long duration. Symptoms of chondroblastoma are nonspecific but are usually present for a few months.2 Osteonecrosis usually exhibits substantial progression over 3 years, but some cases may continue to have mild to moderate pain, without major disability, for a relatively longer period of time. Third, the flattening of the femoral head and loss of contour noted on radiograph in this case is due to the subchondral fracture, which is characteristic of osteonecrosis. Fourth, MRI and scintigraphy findings were inconclusive for both conditions. As described earlier, the MRI picture of osteonecrosis varies widely and is particularly difficult to differentiate from other lesions in late stages, when the characteristic double line sign may not be seen. However, the presence of heterogeneity with bone marrow edema pointed toward chondroblastoma. In our literature review, we found two cases of osteonecrosis of the femoral head simulating chondroblastoma.6 The following differentiating features between these two conditions were described in that report: (1) chondroblastoma is round or oval shape and its borders are not always completely well defined, whereas osteonecrosis does not show any particular shape; and (2) chondroblastoma frequently reaches the subchondral plate without destroying the articular margins, whereas osteonecrosis, when it reaches the subchondral plate, is associated with a subchondral rim and fragmentation or depression of the plate. The characteristic histologic details of conventional chondroblastoma were well seen in this case.3 The designation of a tumor as chondroblastoma depends on the foci, typically rounded, of chondroid matrix. Dystrophic calcification in this cartilaginous island is common. The calcific deposits in the matrix ordinarily outline empty lacunae, producing the typical “chicken-wire calcification.” Ossification of the cartilaginous islands or focal areas of ossification apart from such islands may cause confusion with primary osteoblastic tumors including osteosarcoma. Radiographic and clinical evidence of aggressiveness may help distinguish chondrosarcoma with cellular foci that resemble those of chondroblastoma. Osteosarcoma with a prominent cartilaginous component can be differentiated by the presence of cytologic atypia and substantial mitotic activity.2 There is no accepted standard treatment of chondroblastoma. Curettage alone or combined with packing of the cavity with bone grafting or polymethylmethacrylate or with associated cryosurgery are described.15,23 Marginal resection16 and radiofrequency heat ablation3 are other options. The rate of recurrence after treatment with curettage alone or associated with other procedures is between 10% to 35%.6 The highest recurrence rate was reported in lesions around the hip (five of seven recurrences) in one series.15 Use of an arthroscope, for complete visualization of cavity, has been described.22,24 Several authors report encouraging results with autogenous fibula graft for treating benign lesions of the proximal femur.13,14,18,19 We have used gluteus medius muscle-pedicle bone grafting, particularly in young patients with osteonecrosis of the femoral head, when we believe salvage of the femoral head is important. We similarly treated this patient with musclepedicle bone grafting (Fig 6A). We recommended nonweightbearing crutch walking for 3 months after surgery; by which time the radiographs suggested graft incorporation. We have annually followed the patient. At last followup, 6 years after surgery, she was asymptomatic except for a terminal restriction of internal rotation. There is good remodeling of the femoral head (Fig 6B), but we believe her at risk for developing secondary osteoarthritis.Fig 6A: B. (A) Immediate postoperative anteroposterior radiograph of the hip shows subchondral placement of the bone graft; the size of the lesion is well visualized. (B) An anteroposterior radiograph obtained 6 years after surgery shows complete incorporation of the bone graft without any sign of tumor recurrence. The joint space is well maintained despite flattening of the femoral head margin.Although initially misdiagnosed, the intraoperative diagnosis of chondroblastoma led us to perform an aggressive curettage of the lesion. The vascularized gluteus medius grafting, after elevation of the flattened articular surface, incorporated well and provided good structural support to prevent any further collapse. This ultimately helped to salvage the head without recurrence. Although recurrence usually occurs within the first 3 years after curettage, it has been reported after much longer periods of time and therefore patients should be followed for an extended time.10,20 Acknowledgments The authors thank Ms. Sung Hwa Park and Young Hoon Park, MD, for assistance with followup and data retrieval.