Stability of Transpedicle Screwing for the Osteoporotic Spine: An In Vitro Study of the Mechanical Stability

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The influence of bone mineral density on the stability of transpedicle screwing was studied in the human cadaveric lumber vertebrae. The pull-out force correlated with bone mineral density. The tilting moment (load needed to tilt the screw 4$$ cranially at the screw-plate junction) and the cut-up force (load needed to tip the end plate up by the screw) correlated with bore mineral density, A correlation was also found between the maximum insertion torque of the screw and bone mineral density. The maximum insertion torque correlated with the pull-out force, the tilting moment, and the cut-up force. In the cyclic tiling lest (200 cycles), the mean value of the tilting moment at the 200th cycles was 67.4 $$ 6.1%, compared with the first cycle. The results suggest that preoperative measurement of BMD is necessary far transpedicle screwing in osteoporotic cases, and that the cyclic tilting motion decrease its mechanical stability. The authors have also concluded that the maximum insertion torque could predict the mechanical stability.

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