Abstract: BACKGROUND: Previous reports have shown that percutaneous tripod acetabular support surgery can quickly improve the pain of pelvic metastases and restore the function of hip joint.  
OBJECTIVE: To further explore the clinical efficacy and biomechanical mechanism of percutaneous tripod acetabular support surgery.
METHODS: This study retrospectively included four patients with five acetabular metastases from the First Affiliated Hospital of Guangzhou University of Chinese Medicine, and used Eastern Cooperative Oncology Group (ECOG) and visual analogue scale scores to evaluate the efficacy. Three-dimensional finite element model of pelvis-proximal femur was constructed using three-dimensional finite element technology. The normal group was set as the normal acetabulum; the model group as the affected side acetabulum; and the treatment group as postoperative acetabulum on the affected side. The stress areas of the three groups were observed to analyze the biomechanical principles and mechanisms of percutaneous tripod acetabular support surgery.  
RESULTS AND CONCLUSION: (1) Data analysis: Postoperative ECOG and visual analogue scale pain scores were significantly improved (P < 0.05) in four patients. Among the four patients, one case could walk freely; two cases changed from bed rest to walking with crutches and walkers, and one case still used walkers to walk. (2) Finite element analysis: Compared with the blank group, the local stress of the acetabulum in the two-legged standing position in the model group increased (P < 0.05) , indicating that the stability of the affected acetabulum was poor; the stress concentration was obvious, and the bearing stress effect was not good after the bone in the tumor area was destroyed. Compared with the model group, the stress in the acetabulum in the two-foot standing position in the treatment group decreased (P < 0.05), indicating that the tripod in the affected area of the acetabulum could bear the stress and relieve the stress concentration in the acetabulum and tumor area. Comparing the blank group and the treatment group, it could be seen that the stress concentration of the acetabulum was relieved after operation, and the support brought by the tripod structure was able to achieve the support stress effect of normal bone (P > 0.05). (3) It is concluded that tripod surgery is a new technique for providing safe and effective pain relief for acetabular metastases. This technique provides stable mechanical support for the acetabulum, but its long-term clinical efficacy still needs long-term follow-up evaluation.

Key words: acetabular metastases, percutaneous tripod acetabular support surgery, minimally invasive surgery, three-dimensional finite element analysis, screw, pelvis, biomechanics, pain