Abstract: BACKGROUND: The authors found that when the bilateral percutaneous vertebral augmentation is used to treat osteoporotic vertebral compression fractures with a total bone cement injection of 4 mL or more, different distribution patterns were usually presented on the X-rays; however, there were few reports addressing the effects of these patterns of bone cement distribution on the biomechanical properties of fractural vertebrae.
Objective: To further explore the biomechanical effects of different bone cement filling doses and distribution patterns on biomechanics of the fractural vertebrae using the finite element method.
Methods: The L1-L3 finite element models of osteoporosis were established, and the vertebral compression fractures were simulated in L2. Four distribution patterns bilateral partial fusion (FH type), full fusion (FO type), symmetrical separation (SA type), and asymmetric segregation (SN type) were simulated in 4 and 6 mL injections in the osteoporotic vertebral compression fracture models, respectively, and a total of nine sets of models were obtained. These models were solved under the same boundary conditions and compared with the stress and displacement of the L2 fractural vertebra.
Results and conclusion: (1) The maximum stresses of the nine groups of models were concentrated in the L2 fractural area, and the maximum stress and maximum displacement of each filling model were lower than in the osteoporotic vertebral compression fracture model, indicating the effectiveness of bone cement filling in the treatment of osteoporotic vertebral compression fracture. (2) Compared with 4 mL bone cement filling, 6 mL bone cement filling could significantly reduce the stress of fractured vertebrae and enhance the strength of fractured vertebrae while improving the stability of fractured vertebrae. (3) In the same state of movement, the FH type stress was the least, followed by the SA type, both of which were close. FO type stress was the largest, especially in the lateral bend, which might be associated with its cluster shape resulting in the concentration of lateral stress. In the aspect of displacement, FH type was the least and FO type was the largest. (4) The results show that increased dose of bone cement injection reduces fractural vertebral stress and improves stability, but increases the risk of leakage. Bilateral symmetrical dispersed bone cement (FH type, SA type) is superior in restoring vertebral strength and stability than full fusion (FO type), asymmetric separated (SN type) bone cement. Therefore, when clinically performing bilateral percutaneous vertebral augmentation treatment of osteoporotic vertebral compression fractures, the bilateral symmetric dispersions of the distribution are first guaranteed; priority is recommended for FH type distribution, for appropriate stress stimulation and best stability.

Key words: bone cement, osteoporosis, vertebral compression fractures, percutaneous vertebral augmentation, finite element analysis