BACKGROUND:Currently,pedicle screw fixation technology is recognized as the gold standard for lumbar posterior fusion surgery.However,this technique is associated with several complications such as suboptimal screw placement,loosening,and fracture.Addressing these issues,it requires a thorough investigation into the mechanical properties of screw reinsertion to optimize surgical procedures and enhance success rates and safety.OBJECTIVE:By combining finite element analysis with biomechanical experiments,this study aims to compare and analyze the mechanical performance of traditional trajectory pedicle screws during multiple extraction processes.The goal is to reveal patterns in screw extraction strength over repeated withdrawals,providing scientific insights into the safety and effectiveness of pedicle screw reinsertion for clinicians.METHODS:Based on CT scan data,a three-dimensional reconstruction of the L4 vertebra model was performed.Three-dimensional printing technology was used to create biological experimental samples.A pull-out experiment was conducted according to a screw placement plan.Utilizing CT data and standard pedicle screw parameters,a finite element model of the L4 vertebra and a pedicle screw model(diameter 6.0 mm,length 45 mm)were established.The model was divided into five operating conditions based on screw placement angle and cycles.A finite element model was developed to simulate axial pull-out testing,analyzing stress distribution in the vertebral body and maximum axial pull-out strength of the screw.Mechanics experimental results of three-dimensional printing were compared and analyzed against simulation outcomes.RESULTS AND CONCLUSION:(1)A dedicated experimental setup for pedicle screw extraction from single vertebrae was designed and constructed.(2)In the three-dimensional printing experiment,our groups of models were compared between correctly placed screws and once improperly placed screws.The correctly placed screws group exhibited a maximum pull-out force of(1 422.63±23.80)N.Furthermore,with increasing deviation angles in screw placement,the maximum pull-out forces of each group gradually decreased.(3)Comparing the condition of a single improper nail placement with repositioning the nail correctly,when the offset angle of the improper placement exceeded that of Model 3,correctly repositioning the nail helps to increase the screw's pull-out resistance.(4)Comparing the scenario of two consecutive improper nail placements with repositioning correctly after two improper placements,correctly repositioning the nail reduced the screw's pull-out resistance.Without replacing the screw,it was not advisable to attempt a third nail placement.(5)Experimental pull-out strength of three-dimensional printing correlates significantly with finite element simulation results,with a correlation coefficient of 0.98.There is no significant difference in the outcomes between the two methods(P＞0.05).

Objective·To investigate the reparative effects of photo-crosslinked gelatin methylacrylated(GelMA)hydrogel scaffolds loaded with tauroursodeoxycholic acid(TUDCA)on cartilage defects in rabbit knee joints.Methods·Photo-crosslinked GelMA hydrogel scaffolds loaded with TUDCA were prepared by the ultraviolet light irradiation method.The physicochemical properties of GelMA hydrogel scaffolds were characterized,and the cumulative release rate of TUDCA was determined.A rabbit knee cartilage defect model was established,and 18 rabbits were randomly assigned into three groups,with six rabbits in each group:the control group(no treatment was applied to the cartilage defect),the GelMA group(the cartilage defect was filled with GelMA hydrogel scaffold),and the GelMA+TUDCA group(the cartilage defect was filled with the GelMA hydrogel scaffold loaded with TUDCA).At 12 weeks postoperatively,the concentrations of two inflammatory factors in synovial fluid,tumor necrosis factor-α(TNF-α)and interleukin-1β(IL-1β),were detected by enzyme-linked immunosorbent assay(ELISA).After euthanasia,knee cartilage samples were harvested for gross observation,safranin O-fast green staining,and toluidine blue staining.The repair of the cartilage defects was evaluated according to the International Cartilage Repair Society(ICRS)and Modified O'Driscoll Score(MODS)systems.Immunohistochemical staining was performed to detect type Ⅱ collagen(COL-Ⅱ)protein in the cartilage tissue,and Western blotting was used to assess the protein levels of aggrecan(ACAN)and COL-Ⅱ.Results·GelMA hydrogel scaffolds exhibited a more compact microstructure after ultraviolet light irradiation,along with an suitable mass swelling ratio and compressive modulus.The TUDCA-loaded photo-crosslinked GelMA hydrogel scaffolds demonstrated effective and sustained TUDCA release,achieving a cumulative release rate of 90.2%±2.5%within 28 d.ELISA results showed that compared to the control and GelMA groups,the concentrations of TNF-α and IL-1β in the synovial fluid of the GelMA+TUDCA group were significantly reduced(P<0.001).In the GelMA+TUDCA group,the cartilage defects were nearly fully repaired,with a smooth surface and good integration with the surrounding tissue.The number of newly formed chondrocytes increased,displaying orderly alignment,and the neocartilage exhibited excellent formation.Both ICRS and MODS scores were significantly higher in the GelMA+TUDCA group than those in the control and GelMA groups(P<0.001).Additionally,the expression levels of ACAN and COL-Ⅱ proteins were significantly elevated in the GelMA+TUDCA group compared to the control and GelMA groups(P<0.001).Conclusion·Photo-crosslinked GelMA hydrogel scaffolds loaded with TUDCA can effectively promote the repair of cartilage defects in rabbit knee joints.

Objective·To investigate the reparative effects of photo-crosslinked gelatin methylacrylated(GelMA)hydrogel scaffolds loaded with tauroursodeoxycholic acid(TUDCA)on cartilage defects in rabbit knee joints.Methods·Photo-crosslinked GelMA hydrogel scaffolds loaded with TUDCA were prepared by the ultraviolet light irradiation method.The physicochemical properties of GelMA hydrogel scaffolds were characterized,and the cumulative release rate of TUDCA was determined.A rabbit knee cartilage defect model was established,and 18 rabbits were randomly assigned into three groups,with six rabbits in each group:the control group(no treatment was applied to the cartilage defect),the GelMA group(the cartilage defect was filled with GelMA hydrogel scaffold),and the GelMA+TUDCA group(the cartilage defect was filled with the GelMA hydrogel scaffold loaded with TUDCA).At 12 weeks postoperatively,the concentrations of two inflammatory factors in synovial fluid,tumor necrosis factor-α(TNF-α)and interleukin-1β(IL-1β),were detected by enzyme-linked immunosorbent assay(ELISA).After euthanasia,knee cartilage samples were harvested for gross observation,safranin O-fast green staining,and toluidine blue staining.The repair of the cartilage defects was evaluated according to the International Cartilage Repair Society(ICRS)and Modified O'Driscoll Score(MODS)systems.Immunohistochemical staining was performed to detect type Ⅱ collagen(COL-Ⅱ)protein in the cartilage tissue,and Western blotting was used to assess the protein levels of aggrecan(ACAN)and COL-Ⅱ.Results·GelMA hydrogel scaffolds exhibited a more compact microstructure after ultraviolet light irradiation,along with an suitable mass swelling ratio and compressive modulus.The TUDCA-loaded photo-crosslinked GelMA hydrogel scaffolds demonstrated effective and sustained TUDCA release,achieving a cumulative release rate of 90.2%±2.5%within 28 d.ELISA results showed that compared to the control and GelMA groups,the concentrations of TNF-α and IL-1β in the synovial fluid of the GelMA+TUDCA group were significantly reduced(P<0.001).In the GelMA+TUDCA group,the cartilage defects were nearly fully repaired,with a smooth surface and good integration with the surrounding tissue.The number of newly formed chondrocytes increased,displaying orderly alignment,and the neocartilage exhibited excellent formation.Both ICRS and MODS scores were significantly higher in the GelMA+TUDCA group than those in the control and GelMA groups(P<0.001).Additionally,the expression levels of ACAN and COL-Ⅱ proteins were significantly elevated in the GelMA+TUDCA group compared to the control and GelMA groups(P<0.001).Conclusion·Photo-crosslinked GelMA hydrogel scaffolds loaded with TUDCA can effectively promote the repair of cartilage defects in rabbit knee joints.

BACKGROUND:Currently,pedicle screw fixation technology is recognized as the gold standard for lumbar posterior fusion surgery.However,this technique is associated with several complications such as suboptimal screw placement,loosening,and fracture.Addressing these issues,it requires a thorough investigation into the mechanical properties of screw reinsertion to optimize surgical procedures and enhance success rates and safety.OBJECTIVE:By combining finite element analysis with biomechanical experiments,this study aims to compare and analyze the mechanical performance of traditional trajectory pedicle screws during multiple extraction processes.The goal is to reveal patterns in screw extraction strength over repeated withdrawals,providing scientific insights into the safety and effectiveness of pedicle screw reinsertion for clinicians.METHODS:Based on CT scan data,a three-dimensional reconstruction of the L4 vertebra model was performed.Three-dimensional printing technology was used to create biological experimental samples.A pull-out experiment was conducted according to a screw placement plan.Utilizing CT data and standard pedicle screw parameters,a finite element model of the L4 vertebra and a pedicle screw model(diameter 6.0 mm,length 45 mm)were established.The model was divided into five operating conditions based on screw placement angle and cycles.A finite element model was developed to simulate axial pull-out testing,analyzing stress distribution in the vertebral body and maximum axial pull-out strength of the screw.Mechanics experimental results of three-dimensional printing were compared and analyzed against simulation outcomes.RESULTS AND CONCLUSION:(1)A dedicated experimental setup for pedicle screw extraction from single vertebrae was designed and constructed.(2)In the three-dimensional printing experiment,our groups of models were compared between correctly placed screws and once improperly placed screws.The correctly placed screws group exhibited a maximum pull-out force of(1 422.63±23.80)N.Furthermore,with increasing deviation angles in screw placement,the maximum pull-out forces of each group gradually decreased.(3)Comparing the condition of a single improper nail placement with repositioning the nail correctly,when the offset angle of the improper placement exceeded that of Model 3,correctly repositioning the nail helps to increase the screw's pull-out resistance.(4)Comparing the scenario of two consecutive improper nail placements with repositioning correctly after two improper placements,correctly repositioning the nail reduced the screw's pull-out resistance.Without replacing the screw,it was not advisable to attempt a third nail placement.(5)Experimental pull-out strength of three-dimensional printing correlates significantly with finite element simulation results,with a correlation coefficient of 0.98.There is no significant difference in the outcomes between the two methods(P＞0.05).

A method of establishing the motion trajectory model of flexible puncture needle based on image processing is proposed to accurately measure the motion track of the flexible needle during needle insertion.The dynamic images of needle insertion are collected through the camera system,and the position coordinates of the flexible needle tip during needle insertion are extracted using the image processing morphology technology.Based on the extracted needle tip data,the least square method is employed for curve fitting,and the second-order polynomial model,exponential function model,and bicycle model are established.The analysis on the goodness of fit,residual,and residual sum of squares of different models reveals that the second-order polynomial model is superior to the other two models in exploring the optimal solution of the trajectory model of flexible puncture needle.