Limited Arthrodesis In Cervical Spine With Interbody Fusion Cage-Biomechanical Evaluation And Clinical Application

Due to all kinds of implantation, cervical spine surgery developed very rapidly during the recent 5 decades. Reconstruction of cervical structure become more effective and easy. Interbody cervical fusion cage benefits both spine surgeons and their patients, but the subsidences of cage to adjacent vertebral body reduce the surgical outcomes. This study investigated the biomechanical evaluation of cervical spine instrumented with hollow threaded interbody fusion cage in a special approach and reported a new designed surgical technique and its early clinical application results.Part 1 biomechanical evaluation on primary stability of cervical spine instrumented with interbody fusion cageObjectives: 1. to explore the influence on strength, stiffness and stability of cervical spine instrumented with different diameter thread interbody fusion cage 2. to modify the insertion of cervical interbody fusion cage and to choose the best diameter cage 3. pull-out test of cervical cage 4. to provide rationale of modified surgical technique.Methods: Twelve fresh human cervical spine specimens were used in this study. Cervical spines were instrumented with different diameter cages after different volume of endplate being removed. Experimental stress analysis was applied to analyze and compare the stability and biomechanical relation of the cervical spines. Results: 1. After instrumentation of cervical interbody fusion cage, the strength increases 22%, the flexibility decreases 15%, the stiffness increases 43%, and the migration decreases 20%. They show a significant difference compared with normal cervical spine specimens (p<0.01). 2. The cage of 11-12mm diameter is suggested in modified insertion approach. 3. Modified insertion approach using 11-12mm diameter cage attains the best stability and the least subsidence depth because the cage covers more than 30% of hard endplate and more than 65% contact area between cage and grafting bed. Conclusions: 1. The cervical spine instrumented with interbody fusion cage in the modified insertion approach can get primary stability. 2. Eleven to twelve mm diameter cage is suggested to use in cervical interbody fusion. Part 2 Limited Athrodesis of Cervical Spine Instrumented with Interbody Fusion CageObjectives: A new insertion procedure is designed to obviate the subsidence of cage to adjacent vertebral body of cervical spine. This study reports its surgical technique and early clinical application outcomes.Methods: Thirty-six patients with radiculopathy and myelopathy and clinical instability of cervical disc degenerative disease were treated in the modified insertion approach. Caspar distractor was used to distract the involved vertebral space to normal height and then 2 mm overdistracting was applied to the space. Trephination was performed to remove partial endplate and disc. The Inter Fix cage with 11×12mm or 12×12mm was implanted, and clinical results and imaging outcomes were followed up 1-18 months.Results: This surgical technique is easy to perform, and Caspar distractor facilitates the surgeon to adjust the height of involved disc space during operation. No intraoperative complications were observed. JOA score increases from 10.5 preoperatively to 14.5 postoperatively, the height of disc space increases 3.5±0.5mm after operation immediately, 2.5±0.3mm three months postoperatively, 2.4±0.5mm six months postoperatively, and 2.3±0.6mm twelve months postoperatively, with no significant difference between 3 months and 12 months after operation. No JOA score one year postoperatively decreased. No lucency line or sclerosis line were found around the cage during follow-up. No sign ofcage displacement, extrusion or subsidence to adjacent vertebral body were seen.Conclusions: This surgical fusion procedure with cervical interbody fusion cage is effective and safe. It may mitigate the need for painful hip graft harvest and minimize subsidence of cage to adjacent vertebral body. Its long-term clinical results...