Nano-hydroxyapatite Bone Cement Renovation And Strengthening Of The Pedicle Screw Biomechanics Research

Objective : This study was designed to evaluate the effects of nano-hydroxyapatite on the revision of pedicle screwsMethods : Fourty-eight cadaveric spines from T₁₀-L₅ were harvested, in this study(Thirty-two vertebrals come from four fresh normal adult male cadavers;sixteen vertebrals from two fresh normal adult female cadavers) and were assigned into 4 groups randomly, 24 pedicles per group. AF(4. 50mm X 45mm) screws were first inserted as control in both pedicles of every vertebral body. Control pull-out test of the screws were performed. For each pedicle pairs in Group 1, revision one of AF screw tracks with nano-HAP, and after that, AF screws (4.5mm X 45mm)were inserted then axial pull-out test were performed after 20 minutes , and salvaged of the other of screw tracks with biger. longer AF screw(6.5mm X 50mm). For each pedicle pairs in Group B, revision one of AF screw tracks with nano-HAC, and after that, AF screws(4. 5mmX45mm)were inserted and salvaged of the other of screw tracks with Polymethlmethacrylate(PMMA), AF screws(4. 5mm X 45mm)were reinserted, axial pull-out test were performed after 20 minutes .For each pedicle pairs in Group C, revision one of AF screw tracks with nano-HAC, and after that, AF screws(4. 5mmX45mm)were inserted and salvaged of the other of screw tracks with hydroxyapatite, AF screws(4. 5mmX45mm)were reinserted, axial pull-out test were performed after 20 minutes. For each pedicle pairs in Group D, revision one of AF screw tracks with nano-HAC, and after that, AF screws(4. 5mmX45mm)were inserted , axial pull-out test performed after 20minutes , and salvage of the other of screw tracks with nano-HAC, AF screw(4. 5mm X45mm)were reinserted, axial pull-out test were performed after 24 hours. The maximum pull-out strength and torque were recorded. Results: In group A, the mean maximum pull-out strength of the revision Screws using nano-HAP was 126%of that of the AF control screws, while the mean maximum pull-out strength of the AF screws (6. 5mmX50mm)was 115% of that of control AF screws. The maximum pull-out strength of the revision Screws using nano-HAP was stronger than that of the AF screws(6. 5mmX50mm), there was significant difference (K0. 05) .The mean maximum insertional torque of the the AF was stronger than that of the revision screws using nano-HAC, there was significant difference (K0. 05) . In group B, the mean maximum pull-out strength of the revision Screws using nano-HAC was 134. 2%of that of the AF control screws, while the mean maximum pull-out strength of the revision screws using PMMA was 187. 8% that of control AF screws. The maximum pull-out strength of the revision screws using PMMA was stronger than using nano-HAC, there was significant difference (/K0. 05), The mean maximum insertional torque of the AF was stronger than that of the revision screws using PMMA, there was significant difference (/K0.05) .In group C, the mean maximum pull-out strength of the revision Screws using nano-HAC was 126. 5%of that of the AF control screws, while the mean maximum pull-out strength of the revision screws using HAC was 110. 3% that of control AF screws. The maximum pull-out strength of the revision screws using nano-HAC was stronger than using, HAC, there was significant difference (P\0.05), .In group D, the mean maximum pull-out strength of the revision Screws using nano-HAC which was pull-out after 24 hours was 148%of that of the AF control screws, while the mean maximum pull-out strength of the revision screws using nano-HAP which was pull-out after 15 min was 118.5% that of control AF screws. The maximum pull-out strength of the revision screws using nano-HAC which was pull-out after 24 hours was stronger than using, nano-HAC pull-out after 20 minituer, there was significant difference (p<0.05) .There was linear correlationbetween maximum pull-out force and maximum insertional torque of control AF screws, the coefficient was 0. 78. But there was no linear correlation between maximum pull-out force and maximum insertional torque in revision groups with PMMAx nano-HAC > HAC.Conclusion: (1) The study demonstrated that nano-HAP is good material for revision of failed pedicle screws(2) There was no linear correlation between maximum pull-out force and maximum insertional torque in revision groups with nano-HAC, therefore the maximum insertional torque of revision pedicle screw with PMMA HAC nano-HAC can not predict the maximum pull-out strength of pedicle screw.