| PART I Biomechanical comparison of monosegmental versus short-segmental fixation by pedicle instrumentation in the management of thoracolumbar fracture (AO A3.1)Objective:To testify the biomechanical properties of thoracolumbar burst fracture (AO classification A3.1) treated with monosegmental pedicle instrumentation (MSPI).Methods:Six T10-L2thoracolumbar spine segments were harvested from human donors ranging in age from27to46years (mean39y). Incomplete burst fracture (AO classification A3.1) was made at the level of T12. Monosegmental pedicle instrumentation and short segmental pedicle instrumentation were applied to the specimens sequentially to restore spinal stability. Segmental instability tests were performed on specimens in condition of intact, fractured and MSPI. Range of motions (ROM) in flexion-extension, lateral bending were recorded by a2-camera VICON motion measurement system. The rotational stability was testified by a computer-torsional testing machine.Results:The ROM of MSPI in flexion-extension, lateral bending was0.14±0.02°,0.07±0.020°,0.74±0.13°and0.73±0.22°. The ROM of intact specimen in flexion-extension, lateral bending was0.46±0.05°,1.01±0.23°,1.30±0.31°and1.34±0.24°.The ROM of MSPI was significantly higher than that of intact in flexion-extension, lateral bending (p<0.05). MSPI group was more stable than intact group in flexion-extension, lateral bending. The torsional force of MSPI was3103.00±213.11N and that of intact was2654.75±122.90N. MSPI group was as stable as intact group in axial rotation (p>0.05). The ROM of SSPI in flexion-extension, lateral bending was0.32±0.07°,1.55±0.31°,1.27±0.33°and1.61±0.43°. The ROM of intact specimen in flexion-extension, lateral bending was0.65±0.15°,2.31±0.22°,2.45±0.44°and2.70±0.54°.The ROM of SSPI was significantly higher than that of intact in flexion-extension, lateral bending(p<0.05). SSPI group was more stable than intact group in flexion-extension, lateral bending. The torsional force of MSPI was3184.00±250.40N and that of intact was2654.75±122.90N. SSPI group was as stable as intact group in axial rotation (p>0.05). The SPI of MSPI in flexion-extension and lateral bending was0.94°,0.88°,0.81°and0.92°, respectively. The SPI of SSPI in flexion-extension and lateral bending was0.50°,0.45°,0.52°and0.70°, respectively. The SPI of MSPI was significantly higher than that of SSPI in both flexion-extension and lateral bending (p<0.05). MSPI was more stable than SSPI in both flexion-extension and lateral bending. The torsional force was3103N for MSPI and3184N for SSPI. SSPI was as stable as MSPI in axial rotation (p>0.05).Conclusion:Monosegmental pedicle instrumentation can provide more instant stability than SSPI with respect to the reconstruction of unstable spine (AO classification A3.1) in both flexion-extension and lateral bending. Monosegmental pedicle instrumentation can provide same instant stability as SSPI with respect to the reconstruction of unstable spine (AO classification A3.1) in axial rotation. PART II Biomechanical Comparison of MSPI and SSPI for thoracolumbar burst fractures (AO A3.1) using Finite Element MethodObject:This study was designed to compare the biomechanical effects of two posterior fixations for thoracolumbar burst fractures using the finite element (FE) method.Methods:Four T11-L1FE models, including the intact, the fractured at T12, the monosegment pedicle intrumentation at the level of the fracture and the short-segment pedicle intrumentation with four pedicle screws were created. And four loading condi tions (flexion, extension, lateral bending and torsion) were imposed on these models and deformations in these models under different loading conditions were calculated by finite element method. The biomechanical effects of the two different pedicle screw fixations for thoracolumbar burst fractures were compared and analyzed. Results:The ROM of SSPI (T11-L1) in flexion-extension, lateral bending and was0.762°,0.458°,0.688°,0.601°. The ROM of intact specimen(T11-L1) in flexion-extension, lateral bending and axial rotation was0.768°,1.375°,0.905°,0.630°. The ROM of SSPI group was less than that of intact group in flexion-extension, lateral bending. The ROM of MSPI (T11-T12) in flexion-extension, lateral bending and axial rotation was0.51°,0.114°,0.140°,0.114°. The ROM of intact specimen (T11-T12) in flexion-extension, lateral bending and axial rotation was0.516°,0.515°,0.332°,0.120°. The ROM of MSPI (T11-T12) was less than that of intact(T11-T12) in flexion-extension, lateral bending and axial rotation. Conclusion:MSPI and SSPI could provide desirable stability for the fractured spine. The moment of force loaded onto the pedicle screw and rod of MSPI model was smaller than that of SSPI model. PART Ⅲ Management of thoracolumbar burst fracture:monosegmental fixation versus short-segment fixation-a retrospective controlled study.Objective:To investigate the safety and therapeutic effects of mono-segmental pedicle instrumentation in treating thoracolumbar burst fracture (AO classification:A3.1and A3.2).Methods:A retrospective analysis was conducted on60cases with thoracolumbar burst fracture (AO classification:A3.1and A3.2) between April2005and February2010. Half of the60inpatients were treated with mono-segment pedicle instrumentation (MSPI), and the other half were treated with short-segment pedicle instrumentation (SSPI). The mean operation time, blood loss, visual analog scale (VAS) and vertebral kyphotic angle before and after surgery were compared.Results:In the MSPI group, the mean operation time was90±25min, and the blood loss at operation was180±62ml. The vertebral kyphotic angles were17.3°±9.3°before surgery,6.5°±6.5°one week after surgery, and9.5°±6.4°for the latest follow-up. The VAS scores were7.5±1.4before surgery,2.5±0.7one week after surgery, and1.4±0.8for the latest follow-up. In the SSPI group, the mean operation time was101±28min, and the blood loss at operation was203±88ml. The follow-up duration was12-64months. The vertebral kyphotic angles were16.5°±9.1°before surgery,7.1°±6.9°one week after surgery, and7.5°±5.2°for the latest follow-up. The VAS scores were6.7±1.5before surgery,3.0±0.4one week after surgery, and1.1±0.6for the latest follow-up. There were no statistically significant differences between these two groups in the operation time, blood loss at operation, VAS score and vertebral kyphotic angle before and after surgery (P>0.05). The post-surgical VAS scores and vertebral kyphotic angles were significantly decreased in both groups, compared to before surgery (P＜0.05).Conclusions:It is safe and effective to treat thoracolumbar burst fracture (AO3.1and AO3.2) with MSPI. The mean operation time, blood loss at operation, post-surgical VAS and vertebral kyphotic angle of the MSPI group are similar compared to the SSPI group. |
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