case_images: PMC7724397_01
case_images: Pre-operative image: (a) anteroposterior view of the right hip joint showing a center
  edge angle of 30 , but no developmental dysplasia of the right hip. (b) Dunn view,
  showing a prominent bony bump (thick arrow) on the right femoral neck and findings of
  bone transparency (thin arrow) in the posterior areas of the femoral head. (c) CT scan,
  showing a tumor-like lesion (2.0 cm x 1.5 cm in size) located in the posterior area of
  the femoral head. The axial image shows a lesion with small central foci of mineralized
  matrix, without sclerotic margins and accompanied by cortical erosion and periosteal
  reaction.
case_images: 10.1177_2050313X20978022-fig1.jpg
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case_images: Plain radiographs revealed a radiolucent lesion in the posterior femoral head and cam morphology, with an increased alpha angle (64 ) (Figure 1(a) and (b)). Computed tomography (CT) showed a tumor located in the posterior region of the femoral head (Figure 1(c)).
case_images: Pre-operative multiple echo recombined gradient echo (MERGE) MRI showing an anterior
  labral tear injury (thick arrow) and a bone tumor (thin arrow) behind the femoral
  head.
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case_images: Magnetic resonance imaging (MRI) revealed an apparently non-malignant tumor on the posterior femoral head, as well as a labrum injury (Figure 2).
case_images: Hip arthroscopic findings. (a) Synovial hyperplasia was observed in the joint. The
  labrum was inflamed and thickened, with a complete tear (according to the Mahorn
  classification). (b) Repair of the labrum with two anchors by a round loop suture. (c)
  Exposure of cancellous bone around the cam lesion from the femoral neck to the head,
  followed by resection under computer-navigated guidance. (d), (e), and (f) Planned
  resection range (red areas). Cam resection was performed under computer-navigated
  assistance.
case_images: 10.1177_2050313X20978022-fig3.jpg
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case_images: The tracker device was set on the distal femur using two pins and fluoroscopic-guided point registration was performed; this revealed a labral tear accompanied by severe synovitis and synovial hyperplasia in the hip joint (Figure 3). During osteochondroplasty, the area and depth of the resected section were monitored and evaluated in real time by the computer (Figure 3(d)-(f)).
case_images: The tumor was resected with an en block specimen by posterior approach.
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case_images: After arthroscopic surgery, the tumor was resected using a posterior approach (Figure 4).
case_images: Pathological findings. (a) Low-power view, showing that the tumor consisted of
  reticular woven bone mixed with osteoid. The lesion was surrounded by sclerotic bone.
  (b) High-power view, showing that the reticular woven bone and osteoid were surrounded
  by osteoblasts without nuclear atypia. Osteoclast-like giant cells were also
  observed.
case_images: 10.1177_2050313X20978022-fig5.jpg
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case_images: The osteoid was surrounded by plasmacytoid or epithelioid osteoblasts composed of irregular trabecular bone (Figure 5).
case_images: Post-operative (a) plain X-ray and (b) CT images, confirming that the cam lesion on the
  anterior femoral neck and the tumor on the posterior femoral head had been resected
  completely.
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case_images: Removal of the cam lesion and bone tumor was confirmed by post-operative radiography and CT scanning (Figure 6).