An Evaluation Of Biomechanical Stability Of The Lumbar Spine With Different Surgeries

Objective To study a new dynamic non-fusion system was capable to restore the physiologic motion and stability characteristic of the instable spinal segment . Methods Five fresh bovine lumbar spines were obtained (mean age :one year old, 5 female). The specimens were examined grossly and radiographically to rule out any malignancy or fractures that might interfere with the results. Each motion segments was stripped of muscle ,with care taken to preserve all ligaments, joint capsules,, and bone structures. Each vertebral body of the L4/5 motion segment was potted up to its midbody in polyvinylchloride (pvc) cup using dental cement. Each motion segment was tested according to the loading sequence at five conditions :1) intact; 2) partial destabilization (resection of all ligaments,ligamentum flavum,facet capsule ,and bilateral resection of inferior facets); 3) stabilization with IsobarTM device; 4) complete destabilization wih total laminectomy and; 5)stabilization with pedicle screws and rods. The specimens were mounted in a material testing machine . The specimens were loaded with pure moments of±500Nm in flexion/extension,lateral bending,and axial rotation. The range of motion (ROM) and neutral zone (NZ) of the fixed and adjacent segments were measured. The speciments were measured. The strain slices were inserted into the front of the L3 vertebral body,the specimen was loaded to a maximum of 500N at a displacement rate of 100N/time. The load was applied three times and a load-deformation curve was obtained each time. In the experiment ,the iso-osmia saline was used to keep the specimen moist.A digital goniometer (accuracy of 0.1°and 1-sec dampening; Pro Smart Level ,Wedge Innovations,San Jose, CA ) was used to measure angular deformations in flexion/extension and lateral bending . An on-board rotational transducer ,incorporated into the testing machine,was used to make measurements in axial rotaion . Results the strenge of lumbar adjacent segment Lumbar vertebrae and intervertebral discs'average stress intensity, the normal samples adjacent segment declined 3-8%, 4-6% increase in damage specimen stress, dynamic stress drop rod fixation 5% (P> 0.05), while the arch root rigid fixation of stress significantly increased 11-12% (P <0.05). Conclusion Dynamic ISOBAR TM non-fusion dynamic stabilization system can either maintain the activity of lumbar spine, also can achieve the stability of rigid internal fixation toachieve a dynamic fixed purpose; dynamic rod fixation system is close to rigi-d internal fixation. And the system entirely be made of new type of titanium alloy to prevent the failure of providing the conditions fixed.