Research Of Injectable Calcium Phosphate Cement And Polymethylmethacrylate During Vertebroplasty

OBJECTIVE:1. To investigate the microcosmic constitute changes and biomechanical changes of calcium phosphate cement　(CPC) and polymethylmethacrylate (PMMA) in implanting vertebral body during vertebroplasty, and to compare the interfaces, difference between CPC and PMMA. 2. To investigate the Hemodynamic and blood gas alterations as well as fat embolism during vertebroplasty.METHODS: 1.(calcium phosphate cement　CPC) and (polymethylmethacrylate, PMMA) was implanted into vertebral body, the microcosmic constitute changes of the interfaces between impanted materials and vertebral body were observed by scanning electron microscope,X-ray,CT,and microscope .2. The vertrbral bodies implanted with CPC and PMMA at different stages were tested during axial compressive testing and torsional testing. 3. In four canine, 2.6 mL of polymethylmethacrylate was injected unilaterally into L2. Heart rate, cervical arterial, and blood gas values were recorded before and after injection. The lungs were subjected to postmortem histologic evaluation and compared with lung specimens from two canine that had not undergone vertebroplasty.RESULTS: 1.Conjugation of PMMA and vertebral body was a simple mechanical connection while conjugation of CPC and vertebral body was a biomechanical connection. 2. At early stages, vertebral bodies implanted with PMMA were stronger than normal vertebral bodies as well as vertebral bodies implanted with CPC(P<0.01)in compressive testing,while the stiffness of vertebral bodies implanted with CPC is weaker than that of normal vertebral bodies as well as vertebral bodies implanted with PMMA(P<0.01). After 8 weeks, the stiffness of vertebral bodies implanted with PMMA become low (P<0.01＝0.009),while the stiffness of vertebral bodies implanted with CPC become strong(P<0.05＝0.034) ,but still significantly different from that of normal vertebral bodies.When it comes to the 16th week, the stiffness of vertebral bodies implanted with PMMA become low(P>0.05＝0.710),while the stiffness of vertebral bodies implanted with CPC become strong(P>0.05＝0.648),and there are no significantly differences between them and that of normal vertebral bodies. 3. At early stages, vertebral bodies implanted with PMMAwere stronger than normal vertebral bodies as well as vertebral bodies implanted with CPC(P<0.05=0.03)in torsional testing,while the stiffness of vertebral bodies implanted with CPC is weaker than that of normal vertebral bodies as well as vertebral bodies implanted with PMMA(P<0.05=0.02). After 8 weeks, the stiffness of vertebral bodies implanted with PMMA become low (P<0.05＝0.045),while the stiffness of vertebral bodies implanted with CPC become strong(P>0.05＝0.078),and have no significant differences from that of normal vertebral bodies. When it comes to the 16th week, the stiffness of vertebral bodies implanted with PMMA become low(P>0.05＝0.137),while the stiffness of vertebral bodies implanted with CPC become strong(P>0.05＝0.847),and there are no significantly differences between them and that of normal vertebral bodies. 4. Injection of cement elicited a very rapid decrease in cervical arterial pressure (within 5±2 seconds), lasted for 150±35 seconds. The injection resulted in an increase in partial pressure of carbon dioxide and a decrease in pH and partial pressure of oxygen. The histology showed intravascular fat globules in lung tissue.CONCLUSIONS: 1.As far as histology and biomechanic are concerned ,calcium phosphate cement is believed to be an ideal material in dealing with burst fractures and compressive fractures during vertebroplasty. 2. The results suggest that cement injection during vertebroplasty, can result in arterial pressure decrease and fat embolism in the lungs and that may be a latent complication during vertebroplasty.