Zhao Mou, male, 35 years old, was admitted to the hospital with “unexplained pain and swelling in the left hip for more than one year”. The patient was admitted to the hospital with “unexplained pain in the left hip for more than one year”. The patient had unexplained pain in the left greater trochanter one year ago, limitation of activity, no local redness and swelling, aggravated by activity, and was treated with pain medication in the local hospital to reduce the pain, and the pain was the same as usual after stopping the medication, and the pain in the anterior side of the hip joint appeared six months later with a localized lump, which was treated by plasters and painkillers with no obvious effect. Since the onset of the disease, poor sleep. Specialized examination: swelling and pain around the left hip joint, severe limitation of activity, with obvious limitation of flexion and abduction, pressure and pain around the hip joint, with obvious pressure and pain at the inner edge of the greater trochanter and acetabulum, a hard mass can be palpated at the inner edge of the acetabulum, muscle atrophy in the left lower limb, the upper edge of the kneecap at the 4-finger point is thinner than the contralateral side of the 5cm, the middle thigh is thinner than the contralateral side of the 9cm, and the left foot has normal peripheral blood circulation and sensation. X-ray: left acetabular bone destruction, including the sciatic bone and pubic bone, unclear boundary, reduced density of the medullary cavity, no obvious periosteal reaction, there is a soft tissue mass in the medial and inferior sides, in which there is a bit of flaky bone calcification in the mass below the hip (Fig. 1).CT: left acetabular bone destruction, with a large soft tissue mass, and there is a bit of flaky bone calcification in the mass (Fig. 2). Preliminary diagnosis: chondrosarcoma of the left acetabulum? Chondromyxoid fibroma? Treatment: Admission MRI examination suggested that the left ilium, situs pubis, acetabulum bone destruction combined with soft tissue mass. A malignant tumor was considered (Figure 3). Chest radiograph and CT (No. 44030) showed no obvious abnormalities in both lungs, mediastinum, heart and great vessels. Tumor puncture biopsy was performed under local anesthesia, and postoperative pathology reported cartilaginous mucinous fibroma. Finally, according to the opinion of the patient’s family, the tumor was scraped and cemented under general anesthesia. During the operation, the tumor tissue was an elliptical mass with a diameter of about 8 cm, the tip of which was connected to the pubic bone, and the peritoneum was pushed open to the medial side, so that there was an elliptical mass with a diameter of about 6 cm in the pelvis, the tip of which was connected to the pubic bone, and the ureter was adhered to the tumor tissue. The blood vessels and nerves of the foramen ovale were penetrated into the tumor tissue, and the tumor tissue outside the foramen ovale was completely resected from the outside of the peritoneum from the tip of the pubic bone. Seeing the silver-white granular nodules in the tumor peritoneum, the same method was used to resect the tumor tissue in the inner side of the closed hole, and the tumor tissue in the pubic bone was scraped thoroughly, seeing that the pubic bone was located in the part of the closed hole, i.e., the lower edge of the pubic bone and the pelvic wall of the acetabulum were infringed by the tumor, and the tumor tissue was scraped thoroughly, and the pubic bone was only residual bone cortex, and only articular cartilage was left in the inner part of the lower part of the acetabulum. Three steel pins were inserted into the bottom of the acetabulum, and the X-ray confirmed that the pins were in good position. Bone cement was applied to repair the pubic bone and acetabular defect after tumor removal. X-ray examination again showed that the bone cement fixation was reliable and adequate. After rinsing, 3 layers of abdominal muscle were sutured, inguinal ligament was repaired, abdominal muscle was sutured in the inguinal ligament, the adductor muscle was sutured back to the pubic bone attachment, and the fascia and skin were sutured. Fifteen days after the operation, the patient had left lower limb swelling, and ultrasound examination showed acute thrombosis of the femoral vein and N vein, and symptomatic treatment was given, and the swelling disappeared and the wound healed well. The postoperative pathology report was right acetabular chondroma with signs of malignancy. Postoperative X-ray showed that the tumor was scraped thoroughly and filled with bone cement. Case evaluation] The characteristics of this disease: ① patient is male, 35 years old; ② site of onset is acetabulum, sciatic bone, pubic bone; ③ disease duration is 1 year, gradually aggravated; ④ tumor range is large, local mass, muscle atrophy of the affected limb, activity is obviously limited; ⑤ beat shows that there is a calcification foci within the tumor, soft tissue mass, no periosteal reaction, preoperative puncture and postoperative pathology is not consistent. 1.Diagnosis The diagnosis of this disease was firstly identified as a tumor of cartilage origin, and the comprehensive clinical and imaging data considered chondrosarcoma and chondromucinous fibroma, and the preoperative puncture supported chondromucinous fibroma, and the postoperative pathology reported chondroma malignant transformation. We make a differential diagnosis of the three diseases in the management of this case. Chondromyxoid fibroma is a benign tumor of cartilaginous origin composed of mucoid cartilage, with an age of onset of 10-30 years. It is more common in males than females, often solitary, and is most common in metaphysis and tarsus of long bones, distal and proximal femur, proximal tibia, and distal fibula, especially in proximal tibia, and is less common in epiphysis and diaphysis. The first symptom is pain, the pain can be slow, there are also pressure and swelling, activity limitation, the course of the disease can be 1 week to several years. In children, the onset of the disease is more rapid and spontaneous fractures may occur. This disease is benign tumor, slow growth, the volume will not be very large, there is a reaction bone, most of the stage II active lesions, stage I quiescent lesions are rare, stage III invasive lesions, through the epiphyseal plate invasion of the epiphysis and the surrounding soft tissues are also rare. Imaging characteristics: ① epiphyseal onset; ② eccentric prolongation axis growth, size varies; ③ low density, cortical expansion, edge sclerosis obvious, visible coarse trabeculae; ④ although the source and cartilage, only 13% of cases appear calcification; ⑤ can break through the cortex, accompanied by periostitis, the cortex is semicircular cortical defect, as if bitten, and sometimes periosteum destruction appeared in the soft tissue mass, and the tumor is huge, should pay attention to the differentiation with malignant tumors. When the tumor is huge, it should be distinguished from malignant tumor. For the treatment of this disease, incomplete resection has recurrence in 25% of the cases, so just scraping the lesion is not the best treatment plan, and wide resection or large resection can effectively reduce the recurrence rate. If the lesion invades the soft tissue or epiphysis or shows metastatic foci, it should be regarded as a low-grade malignant chondrosarcoma.