Bone Biomechanics Of Pedicle Screw With Expansion Sleeve In Osteoporotic Synthetic Bone Block

Objective: Osteoporosis sickness is systemic metabolic diseasecharacterized by bone loss, trabecular crack, bone density drop, andsubsequent predispose to severe fracture. In spinal surgery, cause ofosteoporosis，postoperative internal fixation failure rate is relatively high, andprognosis of secondary surgeries are often not satisfied. In order to improvethe stability of the internal fixation in osteoporosis patients, scholars put outmany methods, and have got great progress, but still with some deficiencies.In our research, based on the deficiencies, we designed developed absorbedexpansion sleeve, and to compare the maximum axial pullout of pedicle screwwith expansion sleeve with conventional pedicle screw in osteoporoticsynthetic bone block, evaluate the stability of pedicle screw with expansionsleeve.Methods:60pieces of conventional pedicle screws (Double medicalmaterials co. LTD, Xiamen)were randomly divided into two groupsaverage.One group with expansion sleeve regarded as the experimental group, whileconventional pedicle screw(CPS) as control group. In30osteoporoticsynthetic bone block of consistent standards, pilot holes were prepared inadvance using the same method in all samples. In one pilot holes,verticallyimplant expansion sleeve and screw, make sure the expansion sleeve anchoredtightly by X-ray photography, the other one implant CPS. Compare maximumaxial pullout (Fmax), maximum running torque, lateral pressure between theexperimental group and control group by biomechanical test-machine.Result: The screw was surrounded directly by polyurethane material, theexpansion sleeve anchored tightly in X-ray examination. Screw is vertical toeliminate the error of incline. Fmax: the experimental group (396.43±49.91)N, control group (347.62±23.72) N, t=-5.973,p=0.002.Maximum running torque: the experimental group （3.41±0.82） Nm, control group（1.86±0.41)Nm，t=-3.501,P=0.017. Lateral pressure: the experimental group（25.06±3.15）N, control group（22.13±2.15）N, t=7.925,P＜0.001.According toα=0.05, significant level, P＜0.05.the Fmax, maximum runningtorque and lateral pressure of the experimental group were greater than controlgroup with statistically difference.Conclusion: In spinal implant operation of osteoporosis patients, CPSwith expansion sleeve is more stable than CPS without operation timeprolonged and bleeding increased, and is easy to withdraw the internalfixation. CPS with expansion sleeve has widely application prospect withcharacters of improving the stability of screw in the osteoporotic syntheticbone block and avoiding looseness or breakage of internal fixation.