A modified Edwards instrumentation for unstable fractures of the thoracolumbar spine: an in vitro biomechanical evaluation
- VernacularTitle:改进型Edwards器械固定不稳定胸腰椎骨折的生物力学评价
- Publication Type:Journal Article
- Keywords: Spinal fractures; Internal fixators; Biomechanics; Models,anatomic
- From: Chinese Journal of Orthopaedics 1999;0(07):-
- CountryChina
- Language:Chinese
- Abstract: Objective To evaluat the instant spinal stability and stability following cyclic loading using modified Edwards instrumentation (MEI) for unstable thoracolumbar spine and to compare the spinal stability using Compact Cotrel Dubousset instrumentation (CCD). Methods Twelve thoracolumbar spine specimens(T9-L 5), obtained from fresh human cadavers, were divided into two groups following the production of wedged fracture over the body of L 1. MEI or CCD was applied to the two groups to restore spinal stability. A cyclic load with axial compression (?500 to ?50 N) and axial rotation (10 degrees) was applied to the specimens at rate of 0.5 Hz up to 1 500 cycles. Segmental instability tests were performed for the specimens in intact, injured, fixation and following cyclic loading. The instability test applied pure moments in flexion/extension, left/right lateral bending and left/right axial rotation to the specimen. The maximum moment was 10 N?m in each case. Ranges of motion (ROMs) were measured using stereophotogrammetry. Results 1)The compressive fractures at L 1 vertebral body resulted in unstability at thoracolumbar segment in all six directions. 2) T 12-L 2 segmental ROMs were smaller than those of the control in flexion, extension and lateral bending, but larger in axial rotation following MEI fixation. The ROMs increased in all directions following fatigue, especially became significantly larger in lateral bending. 3)The segmental ROMs decreased significantly in all six directions following CCD fixation, and even following fatigue except in right lateral bending. 4)ROMs with CCD fixation were significantly smaller than MEI fixation in left axial rotation, and in lateral bending and axial rotation following fatigue. Conclusion MEI provides instant stability in flexion, extension and lateral bending, but it does not reconstruct spinal stability in axial rotation. MEI fixation becomes unstable in lateral bending following cyclic loading. CCD is stronger biomechanically than MEI in lateral bending and axial rotation, either for instant stability or stability following cyclic loading. Orthosis or cast should be applied to the patient with MEI fixation to strengthen spinal stability.