ABSTRACT
Objective:To investigate the effect in lumbar mobility and stress of the facet joint and end plate after implantation of the movable artificial lumbar spine so as to lay a biomechanical foundation for its clinical application.Methods:Total lumbar CT data of a healthy adult male were selected to construct a finite element analysis model and its effectiveness was validated (physiological group). Two groups were replicated after removing the L 3 vertebral body and adjacent discs of the model in physiological group. One group was placed with each component of the movable artificial lumbar spine to construct the non-fusion model (non-fusion group). The other group was placed with titanium cage, titanium plate and other to construct the fusion model (fusion group). The models in the three groups were loaded with 500 N axial load and 10 Nm axial load, and the torque load was used to simulate the movement in six directions: forward flexion, backward extension, left and right lateral bending, and left and right torsion. The lumbar mobility and stress peak and distribution of the proximal facet joints (J 1-2, J 4-5), L 2 inferior endplate and L4 superior endplate at the three model operating sites (L 2-3, L 3-4) and adjacent segments (L 1-2, L 4-5) under the same conditions were compared. Results:The range of motions of the surgical site in flexion, extension, left bending, right bending, left torsion and right torsion were L 2-3of 3.9°-8.7° and L 3-4 of 3.6°-8.4° in non-fusion group, significantly increased compared with fusion group (L 2-3 0.1°-0.2°, L 3-4 0.1°-0.1°) and slightly increased compared with physiological group (L 2-3 2.3°-6.0°, L 3-4 2.3°-7.1°). The range of motions of the adjacent segments in the above six directions were L 1-2 of 1.4°-4.3° and L 4-5 of 1.4°-6.0° in non-fusion group, smaller than those in fusion group (L 1-2 2.1°-6.1°, L 4-5 3.3°-8.6°) and similar to those in physiological group (L 2-3 2.3°-6.0°, L 3-4 2.3°-7.1°). The peak values of von Mises stress in the proximal facet joints were J 1-2 of 7.07-19.21 MPa and J 4-5of 6.12-12.99 MPa in non-fusion group, similar to those in physiological group (J 1-2 8.42-18.53 MPa, J 4-5 7.49-11.70 MPa) and smaller than those in fusion group (J 1-2 10.54-21.16 MPa, J 4-5 10.63-16.13 MPa). The maximum von Mises stress of the L 2 inferior endplate and L 4 superior endplate in the above six directions was 29.39-54.72 MPa and 32.31-47.87 MPa in non-fusion group, significantly increased compared with the L 2 inferior endplate (21.20-42.07 MPa), L 4 superior endplate (22.50-36.76 MPa) and L 2 inferior endplate (11.04-29.55 MPa) in fusion group and the L 4 superior endplate (13.12-21.32 MPa) in physiological group. Conclusion:Compared with the traditional fusion prostheses, the placement of the movable artificial lumbar spine can reconstruct the range of motion of the surgical site in the direction of flexion, extension, lateral bending and torsion, greatly reduce the impact on the stress of adjacent facet joints and the range of motion of adjacent segments, and theoretically reduce the incidence of prosthesis subsidence.
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Objective:To investigate the processing accuracy and biomechanical properties of 3D printed artificial bone trabeculae with different porosity generated by the Voronoi Tessellation algorithm, and to provide a reference for improving the biomechanical properties of titanium alloy implants in orthopedics.Methods:A healthy adult male volunteer (aged: 30 years, tall: 175 cm and weight: 70 kg) was selected to collect CT scan data of the lumbar spine. Five kinds of biomimetic artificial bone trabeculae with different porosity were generated using the Voronoi Tessellation algorithm, and divided into Tra_A (73.7%), Tra_B (74.1%), Tra_C (80.0%), Tra_D (80.2%) and Tra_E (85.7%) groups according to the porosity. Selective laser melting (SLM) 3D printing technology was used to process trabecular bone structures with different porosity into titanium alloy prosthesis with a diameter of 18 mm and a height of 20 mm. Each group had 3 samples. The internal structure of each sample was observed by industrial microscope, and the actual porosity of artificial bone trabecular of each group was calculated and compared with the theoretical porosity to evaluate the machining accuracy of artificial bone trabecular with different porosity. Finally, the ultimate load, yield strength and elastic modulus of each sample were evaluated by in vitro mechanical test, and the biomechanical properties of artificial bone trabeculae with different porosity were evaluated.Results:There were no cracks, fracture of connecting rod or accumulation of titanium alloy powder in all specimens. The average actual porosity of the five groups of artificial bone trabecular specimens was 66.0%, 65.5%, 71.8%, 72.5% and 78.1%, respectively. Compared with the theoretical porosity, it was smaller by 10.5%, 11.6%, 10.2%, 9.7% and 8.8%, respectively. In the in vitro mechanical tests for the five groups of artificial bone trabecular specimens, the mean value of ultimate load was 23.6 kN, 18.9 kN, 17.0 kN, 16.3 kN, 10.7 kN, respectively; the mean value of yield strength was 72.2 MPa, 58.7 MPa, 54.9 MPa, 52.2 MPa, and 36.1 MPa, respectively; the mean value of the actual elastic modulus was 7.5 GPa, 6.3 GPa, 4.5 GPa, 4.3 GPa and 2.4 GPa, respectively. With the increase of the porosity of artificial bone trabeculae, all three indicators above showed a decreasing trend. Conclusions:The artificial bone trabeculae generated by the Voronoi Tessellation algorithm and printed by SLM 3D have better machining quality. With the increase of porosity, the processing precision of the titanium alloy artificial bone tray specimens is better. Limit load, yield light and elastic modulus of artificial bone trabecula decrease with the increase of porosity.
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Objective@#To evaluate our replantation and functional reconstruction of amputated lower extremities.@*Methods@#From February 2013 to October 2017, 13 patients with an amputated lower extremity were treated at Orthopaedic Department, The 960th Hospital of the PLA Joint Logistics Support Force. They were 10 males and 3 females, aged from 15 to 63 years (average, 39 years). In all the patients, large segmental shortening and extremity replantation was conducted at the first stage and Ilizarov extremity lengthening at the secondary stage. After desired extension was achieved, the frame of Ilizarov external fixator was removed and replaced by external fixation with a locking plate under closed reduction. Postoperatively, functions of the knee and ankle joints, sensory recovery of the foot sole, length and appearance of the extremity were observed.@*Results@#All the 13 patients were followed up for 12 to 24 months (average, 16 months). All the limb replants survived well. Of them, 12 were satisfied with their weight-bearing walking and therapeutic outcomes.@*Conclusions@#For an amputated lower extremity, the first-stage shortening and replantation can result in fine extremity salvage and the secondary Ilizarov extremity lengthening can lead to fine therapeutic outcomes.
ABSTRACT
Objective To evaluate our replantation and functional reconstruction of amputated lower extremities.Methods From February 2013 to October 2017,13 patients with an amputated lower extremity were treated at Orthopaedic Department,The 960th Hospital of the PLA Joint Logistics Support Force.They were 10 males and 3 females,aged from 15 to 63 years (average,39 years).In all the patients,large segmental shortening and extremity replantation was conducted at the first stage and Ilizarov extremity lengthening at the secondary stage.After desired extension was achieved,the frame of Ilizarov external fixator was removed and replaced by external fixation with a locking plate under closed reduction.Postoperatively,functions of the knee and ankle joints,sensory recovery of the foot sole,length and appearance of the extremity were observed.Results All the 13 patients were followed up for 12 to 24 months (average,16 months).All the limb replants survived well.Of them,12 were satisfied with their weight-bearing walking and therapeutic outcomes.Conclusions For an amputated lower extremity,the first-stage shortening and replantation can result in fine extremity salvage and the secondary Ilizarov extremity lengthening can lead to fine therapeutic outcomes.