Abstract: BACKGROUND: At present, the possible risk factors and pathogenesis of the recurrent vertebral fractures after injection of calcium phosphate cement in percutaneous kyphoplasty are still controversial. The main points are related to the clinical characteristics of patients and surgical related factors.
OBJECTIVE: To investigate the risk factors of the recurrent fractures in patients with osteoporotic vertebral compression fracture after injection of calcium phosphate cement in percutaneous kyphoplasty. 
METHODS: The clinical data of 162 patients (191 vertebrae) with osteoporotic vertebral compression fractures admitted to the Third Affiliated Hospital of Anhui Medical University from February 2016 to February 2018 were retrospectively analyzed. All patients, aged 51-88 years, were treated with kyphoplasty and injection of calcium phosphate cement. All patients were followed up for more than 2 years. There were 34 cases (44 vertebrae) with refracture after operation, and 128 cases (147 vertebrae) without refracture as control group. The age, sex ratio, bone cement injection volume, unilateral or bilateral puncture, symmetrical distribution of bone cement across the midline, leakage of bone cement, contact of bone cement with upper and lower endplates, number of fractured vertebral bodies before operation, distribution of fractured vertebral bodies before operation, compression degree of fracture before operation, taking anti-osteoporosis drugs after operation, bone mineral density before operation and old vertebral fractures before operation, Cobb angle change after operation and recovery rate of anterior edge height after operation were compared between the two groups. Univariate independent sample t-test and multivariate logistic regression analysis were performed.
RESULTS AND CONCLUSION: (1) There were significant differences between the two groups in age, symmetrical distribution of bone cement across the midline and distribution of bone cement on endplate (P < 0.05), but there were no significant differences in other indexes (P > 0.05). (2) Multivariate logistic regression analysis showed that age (P=0.006, OR=1.086), bone cement contact with the upper and lower endplates (P=0.025, OR=2.516) and bone cement in the vertebral body without midline symmetry (P=0.012, OR=0.344) were independent risk factors for recurrent vertebral fractures. (3) The results showed that the elderly status of patients with osteoporotic vertebral compression fractures, bone cement contacting the upper and lower endplates at the same time and not crossing the midline symmetry were independent risk factors for the new fracture after percutaneous kyphoplasty. The different distribution of bone cement in the vertebrae affected the new fracture by changing the internal stress of the vertebrae and the spinal line of force.

Key words: percutaneous kyphoplasty, calcium phosphate cement, osteoporosis, vertebral compression fracture, recurrent fractures, advanced age, bone cement distribution, stress