Biomechanical Study Based On Pressure Sensitive Film Materials And Immature Porcine Upper Thoracic Spine Segment Models

Objective: The present study analyzed the change and distribution of pressure between each intervertebral disc of upper thoracic vertebra of mini pigs.We can identify biomechanical characteristics of different segments of the spine and obtain a reliable foundation for subsequent experiments of scoliosis.This study can also guide therapeutic methods based on biomechanical characteristics.Methods:1 PartⅠ: We selected twelve mini pigs spines randomly.Combined with experimental images of CT examination and specimens,we measured transverse diameter and sagittal diameter of upper thoracic end plates to identify their morphological characteristics.2 Part II: The vertebral columns of 12 mini pigs were divided into two groups(six in each group).In one group,T1-T2,T3-T4,T5-T6,and T7-T8 segments were taken;in the other group,T2-T3,T4-T5,T6-T7,and T8-T9 segments were taken.The sum of the data from both groups represented the complete upper thoracic vertebra data.A BOSE biomechanical machine and pressure sensitive film were used to measure the pressure on the vertebral columns when they were subjected to vertical pressures of 100 N,150 N,and200 N to each segment,5° flexion,or extension or lateral bending.A Fujitsu densitometer(Japan)was used to measure the pressure on each direction of the pressure sensitive film.SPSS13.0 was used to perform paired-sample t-tests to analyze experimental data.3 Part III: vertebral destructive experiments.The upper thoracic segments were connected to the biomechanical testing machine,5 degree left lateral bending was simulated.We increased the compressive load gradually until thevertebral began to destruction.The pressure values were recorded.HE staining and masson staining were used to observe the intervertebral disc tissue.Results: 1 PartⅠ: Upper thoracic spine segments have similar morphological characteristics(similar bean-shaped),until the T9-T10 segment turn into a heart shape.Morphological change is a primary way to define the scope of upper thoracic spine.We defined T1-2 to T8-9 as upper thoracic spine based on this study.2 Part II: With the increasing of the compressive load,pressures on motion segments showed an increasing trend(P<0.05);Variation analysis of the average pressures of overall annulus : in T7-8 and T8-9segments,the increase values of the average pressures didn’t change(P>0.05)with the increasing of compressive load.But in the remaining motion segments,the increase values of the average pressures decreased with the increasing of compressive load(P<0.05);Pressures on anterior annulus of motion segments increased under anterior flexion(P<0.05),but pressures on posterior annulus of some motion segments didn’t decrease,on the contrary,they kept invariant(P>0.05)or increased(P<0.05).Pressures on anterior annulus of motion segments decreased(P<0.05)under posterior extension,but pressures on posterior annulus of some motion segments didn’t increase,on the contrary,they kept invariant(P>0.05)or decreased(P<0.05).Pressures on concave side increased(P<0.05)significantly under lateral bending.3 Part III:Destruction of the concave side was more obvious,bony tissue was crushed but cartilage tissues were better preserved.Conclusions:1 Every motion segment of upper thoracic spine has unique morphological characteristics and biomechanical characteristics,the posterior side of the vertebral body plays an important role in the movement of upper thoracic spine and stress distribution.2 Pressures on concave side increases significantly under lateral bending,indicates that asymmetrical stress may be an important reason for the progression of scoliosis.This result fits in with Hueter-Volkmann law.Improve the asymmetrical stress is an important way to cure scoliosis,and itshould in line with unique morphological characteristics of motionsegments of upper thoracic spine.3 Gravity is an important factor for the progress of scoliosis,but meanwhile,the effect of the posterior side of the vertebral body is assignable,both of them can decrease the pressure on intervertebral disc todelay the progress of scoliosis.4 Cartilage tissue and intervertebral disc have better bearing ability,vertebral compression failure is due to crush destruction of bony tissues.5 Trauma can induce scoliosis,the harm of cell columns may be an important reason to this kind of scoliosis.Long-term pressure on cell columns and other growth structures may be an important progress factor of scoliosis..