Design And Biomechanical Analysis Of Centrum-vertebra-fracture-repairing Absorbable Supporting Plugger

Objective: To design a Centrum-vertebra-fracture-repairing absorbable supporting plugger(CASP) used for reconstructing the height and the prop function of traumatic thoracolumbar fracture vertebrae bodies. Combined with posterior short-segment transpedicular fixation system, CASP may provide a better initial stability of the spinal construction and prevent the implant failure of posterior short-segment transpedicular instrumentation, and reduce incidence rate of the loss of corrective angle. To evaluate the mechanical property of the CASP in vitro, and evaluate the biomechanical effects of CASP in combined with instrumentation on the stability of the spine-device construct.Methods: Design and manufacture Centrum-vertebra-fracture-repairing absorbable supporting plugger. 6 CASP were test using a material testing machine and it's mechanical character (strength and stiffness) were mesured. Thirty-two fresh porcine spine specimens (T13-L3) were harvested and divided into four groups: Intact, Centrum-vertebra-fracture-repairing absorbable supporting plugger in combination with Short segment pedicle instrumentation group (CS group), Short segment pedicle instrumentation group (SSPI group), Anterior instrumentation group (AI group). The L₁ burst fracture model was created on a bionix material testing machine(MTS858 Bionix test system,America). During the expriment, the axial compression, flexion, extension, left bending, right bending loads were applied to the specimens. A load-displacement plots were generated and used to calculate stiffness of axial compression, flexion, extension, left bending, right bending for these spine-device constructs to document spinal stability.Result:1．Based on the parameters of radiographic and anatomical measurement, we have design and manufacture a series Centrum-vertebra-fracture-repairing absorbable supporting plugger . A 25．0×7．5×9．0(length×width×height,mm) CASP were tested in the present study. The compressing strength of CASP was 4722．64±183．08N, which maks it can meet the demands of thoracolumbar biomechanical stability.2．The stiffness under different loadings in the fractured models decreased distinctively than the intact spine. The thoracolumbar injury model is a AO Type A3 burst fracture.3．Axial Compression: Axial compression stiffness of the SSPI group was 166．05±18．29N/mm. However, CASP with posterior instrumentation significantly increased the axial compression stiffness to 214．81±26．95N/mm, which is significantly higher than the the AI group (164．17±15．66N/mm) and intact spine (141．01±17．09N/mm) too. SSPI group was not significantly different from the AI group. The CASP increased the axial compression stiffness of device-spine constructs with posterior instrumentation.4．Flexion: The CS group had flexion stiffness of 177．24±19．71 N/mm,which is significantly higher than the SSPI group(122．79±25．07 N/mm) , and at the same level as the AI group. The SSPI group had greater value than the Intact group, but insignificantly.5．Extension: The CS and SSPI groups had extension stiffness of 156．22±31．91 N/mm and 145．45±25．33 N/mm, respectively. They were all significantly greater than the Intact and AI groups, and, there was not significant difference between the SSPI and CS groups. The AI group had extension stiffness of 84．24±6．44 N/mm, which was not significantly different from Intact group(69．66±19．27 N/mm). The CS and SSPI were stiffer in extension as a result of the presence of posterior instrumentation.6．Bending: The benging stiffness of the three manipulations were not significantly different fron each other,which were all higher than the Intact groupConclusion:1．Based on the parameters of radiographic and anatomical measurement, we have manufacted one of the Centrum-vertebra-fracture-repairing absorbable supporting plugger. It can meet the demands of thoracolumbar biomechanical stability.2．Centrum-vertebra-fracture-repairing absorbable supporting plugger with bone graft can complement the body defect and provide the stability of anterior column.3．In the porcine spine, the short-segment posterior fixation with Centrum-vertebra-fracture-repairing absorbable supporting pluggers had better initial biomechanical benefit than any other methods.4．The Centrum-vertebra-fracture-repairing absorbable supporting pluggers combined with posterior instrumentation increased the spinal construct stability during compression, flexion, and extension. According to the comparisons in this study, the CASP may provide the anterior support and prevent the implant failure of posterior instrumentation. The Centrum-vertebra-fracture-repairing absorbable supporting plugger may be a feasible substitute for the anterior role in future operative treatment of collapsed vertebral bodies.