[Biomechanical study of polymethyl methacrylate bone cement and allogeneic bone for strengthening sheep vertebrae].

OBJECTIVE: To investigate the feasibility and mechanical properties of polymethyl methacrylate (PMMA) bone cement and allogeneic bone mixture to strengthen sheep vertebrae with osteoporotic compression fracture.
METHODS: A total of 75 lumbar vertebrae (L 1-L 5) of adult goats was harvested to prepare the osteoporotic vertebral body model by decalcification. The volume of vertebral body and the weight and bone density before and after decalcification were measured. And the failure strength, failure displacement, and stiffness were tested by using a mechanical tester. Then the vertebral compression fracture models were prepared and divided into 3 groups ( n=25). The vertebral bodies were injected with allogeneic bone in group A, PMMA bone cement in group B, and mixture of allogeneic bone and PMMA bone cement in a ratio of 1∶1 in group C. After CT observation of the implant distribution in the vertebral body, the failure strength, failure displacement, and stiffness of the vertebral body were measured again.
RESULTS: There was no significant difference in weight, bone density, and volume of vertebral bodies before decalcification between groups ( P>0.05). After decalcification, there was no significant difference in bone density, decreasing rate, and weight between groups ( P>0.05). There were significant differences in vertebral body weight and bone mineral density between pre- and post-decalcification in 3 groups ( P<0.05). CT showed that the implants in each group were evenly distributed in the vertebral body with no leakage. Before fracture, the differences in vertebral body failure strength, failure displacement, and stiffness between groups were not significant ( P>0.05). After augmentation, the failure displacement of group A was significantly greater than that of groups B and C, and the failure strength and stiffness were less than those of groups B and C, the failure displacement of group C was greater than that of group B, and the failure strength and stiffness were less than those of group B, the differences between groups were significant ( P<0.05). Except for the failure strength of group A ( P>0.05), the differences in the failure strength, failure displacement, and stiffness before fracture and after augmentation in the other groups were significant ( P<0.05).
CONCLUSION: The mixture of allogeneic bone and PMMA bone cement in a ratio of 1∶1 can improve the strength of the vertebral body of sheep osteoporotic compression fractures and restore the initial stiffness of the vertebral body. It has good mechanical properties and can be used as one of the filling materials in percutaneous vertebroplasty.