Application Study Of Pedicle Screw On Low BMD Vertebrae

Objectives: By biomechanical study of f different pedicle screws' (U1, U2, RF, SF1, SF2) stability on spinal specimen, discussing the relationship between design parameter of screw, insertion torque and BMD, providing the theoretical foundation for application of pedicle screw on osteoporotic patients.Methods: collecting six fixed lumbar cadavers, determining the effects of design parameter, insertion torque and etc on fixation stability under various BMD by using biomechanical ways.Results: (according to in vitro study)1.There is a significant difference among pullout strength of 5 different screws (U1, U2, RF, SF1, SF2). (P<0.05)2.There is a gradual accretion in lumbar segments from top to down. It is also in axial stiffness.3.BMD of bone will directly affect the intensity (measured by pullout strength) of screw. There is significant difference between normal group and osteoporosis group. (P<0.05).4.The fixation intensity is in direct relation with insertion torque, thebigger the moment, the greater the fastness, oid there is also positive relation between it and BMD(r=0.936).5.Among specimen of low BMD, U2 has the greatest pullout strengthen of 5 different screws.Conclusions: There is a close relationship between type of screw, BMD and stability. BMD has the positive relationship with contra-strength and insertion torque. In this study, the "U"-type screw displays the best fixation effect on specimen of low BMD.