Design And Biomechanical Evaluation、Primary Application Of Unidirectional Growth Ring Of Spine

ObjectiveTo improve the instrumentation growing rods of sliding pedicle screw system,a new unidirectional snap ring design is added,and a biomechanical experiment is provided to provide a theoretical basis for further improvement of the system and preliminary clinical application.Methods1.Design the unidirectional growth ring of spine:According to some literatures,we put forward design ideas,and draw blueprint.Hengjie company is commissioned to manufacture the sample.2.The biomechanical evaluation of unidirectional growth ring of spine:Ten fresh adult pig spine specimens(T1-T6)were selected.The bony structures(T1 and T6 vertebrae)at the upper and lower ends of the specimens were respectively screwed into four fixing nails for fixation on the fixture.Each specimen was subjected to a random sequence of biomechanical tests in 3 groups:(1)normal group: normal specimen;(2)chute group:place the pedicle screw pedicle screw in T2 at the tip,the bilateral pedicle fixed nail in T5 at the tail,orthopedic titanium rods placed on both sides;(3)snap ring group: on the basis of chute group,remove the T2 right slide nails,re-insert the pedicle fixed nail with a snap ring,orthopedic titanium rods placed on both sides.The specimen was fixed on a kuka robot,and a load of 300 N was applied to the specimen.Pressure and tensile tests were performed on each group.Changes in length or displacement of each specimen under tension and compression were recorded.Then,statistical analysis was carried out to compare the differences in the length of compression and extension between the snap ring group and the normal group and the chute group under the same load.3.The primary application of unidirectional growth ring of spine:According to the statistics of patients with scoliosis who underwent surgery in our hospital from 2015 to 2017 with complete follow-up data,8 patients were enrolled,including 6 females and 2 males,with an average age of 7.6 years(range 5 to 10 years).Record the preoperative and postoperative immediate,postoperative 6 months and 1 year postoperative shoulder balance index: Cobb angle,shoulder height difference,clavicle angle,T1 tilt angle and first rib tilt angle.Statistical analysis of the indicators,compare the differences.Results1.In the tensile test,the average length of displacement in the normal group was 2.62 mm under loading physiological load(300N),the average displacement length of the chute group was 2.30 mm,and the displacement length of snap ring group was 2.29 mm.There were significant differences between the two groups(P <0.05).There was no significant difference in the extension length between the chute group and the snap ring group.2.In the compression test,the average displacement length of the normal group was 3.44 mm under the load of physiological load(300N),the average displacement length of the chute group was 3.20 mm,and the average displacement length of the snap ring group was 2.13 mm.There was significant difference between the compression length of chute group and snap ring group(P <0.05).3.In the initial clinical application,all children were successfully completed the operation,with an average follow-up time of 18.3 months(12 to 26 months).Observations: Cobb angle,shoulder height difference,clavicle angle,T1 tilt angle and the first rib tilt angle,preoperative and postoperative contrast,the indicators were significantly different,the difference was statistically significant(P <0.05);postoperative Immediately,after 6 months and 1 year after the index were no significant differences.All children with the last follow-up X-ray showed spine growth,the upper and lower ends reserved for the connecting rod have been sliding accordingly,children’s height growth and well-developed.Conclusion1.The unidirectional growth ring of spine can achieve one-way sliding effect.2.The unidirectional growth ring of spine have a role in maintaining postoperative patient shoulder balance.