The Reliability of Pedicle Screw Fixation in the Spine Surgery with Severe Osteoporosis

Abstract：Objective To evaluate the fixation of pedicle screw in the lumbar spine with severe osteoporosis,further to provide theoretical evidence for clinical application of pedicle screw in patient with severe osteoporosis. Methods Fresh hu-man cadaver spines were used. Two of them were normal and four were severe osteoporosis,according to the value of bone min-eral density. The vertebra was bilaterally instrumented pedicle screws,resulting in 24 screws in normal BMD group,as the con-trol group. The vertebrae at severe osteoporosis level was bilaterally instrumented with pedicle screws according to three proto-cols,including pedicle screw without augmentation,pedicle screw with calcium phosphate cement( CPC)augmentation,pedicle screw with poly( methyl methacrylate)( PMMA)augmentation,as group PS,group CPC/PS and group PMMA/PS,respectively. Sixteen pedicles per protocol were obtained in each group. Screw pullout tests were conducted. On the load-stroke curve,the maximum pullout strength,stiffness and energy absorption were determined. The differences between groups were compared. Results With the BMD decreasing in severe osteoporosis level,the maximum pullout strength,the stiffness and the absorbed energy of pedicle screw were correspondingly significantly lower than those of the control group(P<0. 005). Also,the above three indexes of PMMA/PS group were significantly higher than those of PS and CPC/PS group(P<0. 001),but no signifi-cance difference was found between PS and CPC/PS group in these indexes(P>0. 05)except but the pullout strength(P<0. 05). Conclusion Under the condition of severe osteoporosis,the purchase strength of pedicle screw decreases significantly,it should not be used alone in the spine surgery of internal fixation. After being augmented with PMMA,the stability of pedicle screw can be improved.