Figure 1 Anteroposterior X ray images of recurrent left proximal femoral BCA before and after treatment. A is X ray image of left femur before treatment， showing BCA recurrence after curettage and intramedullary nail fixation， with osteolytic destruction of the left proximal femur； B is X ray image of bilateral hips after two years of subcutaneous injection of denosumab， showing the lesions disappearing

Figure 2 Images of typical case one with recurrent BC of the proximal femur before and after treatment. A is the anteroposterior X-ray image of bilateral hips before surgery， showing proximal pathological fracture of the left femur； B is the anteroposterior X-ray image of bilateral hips after surgery， showing internal fixation with cannulated crews； C is the HE staining of the tumor tissue of the left hip joint （×50），showing cyst wall formed by surrounding fibroblasts and fibrous tissue proliferation， a small amount of inflammatory cells and osteoclaseslike giant cells infiltration， and peripheral bone tissue proliferation； D is the anteroposterior X-ray image of bilateral hips three years after surgery， showing pathological fracture of left femoral neck and recurrence of bone cyst； E is the anteroposterior X-ray image of bilateral hips after left hip replacement

Figure 3 Anteroposterior radiographs of the left shoulder of typical case two with recurrent BC of proximal humerus before and after treatment. A is the image of left proximal humerus after curetage and bone grafting； B is the image two years after the primary surgery， showing varus deformity of the left upper limb； C is the image three years after the primary surgery， showing lateral epiphyseal block of the left humerus

Figure 4 Images of typical case three before and after treatment of postoperative recurrence of BCA in the right proximal femur. A is HE staining of the tumor tissue of the right hip joint （×200）， showing more inflammatory granulation tissue and a small number of multinucleated giant cells in the lesion； B is the full-length anteroposterior X-ray image of both lower limbs， showing the right proximal femur after curettage， bone grafting and plate fixation for osteolytic destruction； C is anteroposterior X-ray image of bilateral hips one year after the plate fixation， showing osteolytic destruction at the original bone graft site； D is anteroposterior X-ray image of bilateral hips three years after the plate fixation， showing elastic nail internal fixation at the right proximal femur with plate removed； E is anteroposterior X-ray image of the right hip one year after the nail fixation， showing the lesions disappeared and the bone cortex thickened