Abstract: Objective To explore the etiology and pathogenesis of idiopathic scoliosis by creating experimental scoliosis as well as validate the hypothesis of spinal growth imbalance.To determine the magnitude ranges of spinal tether force and observe the changes of mini-pig's spinal deformity in three-dimensional sections by posterior transpedicle screws with Nd-Fe-B magnetic materials.Methods Sixteen mini-pigs(female,4 weeks old,(7.54±0.46)kg were randomly arranged averagely into tethering group and control group.Left-side posterior transpedicle screws(25 mm) with magnets were placed into vertebrae from T₈ to T₁₀ in tethering groups and maintained the proper magnetic polarity within distance of 5 mm;in the control group pigs underwent operation only using pedicle screws;they were all checked by A-P and lateral X-ray films every 4 weeks until 12 weeks to measure items responded to degrees of spinal deformity including weights and Cobb angles in coronal section and sagittal kyphosis and the heights of apex vertebral(T₉) between two sides as well as magnitudes of magnetic forces among the involved vertebrae.Results Mean weights of mini-pig increased about 2 times in 12 weeks(21.05±1.67)kg in tethering group and(21.75kg±1.67)kg in control group,P>0.05).The heights of T₉ vertebral increased double during 12 weeks from 6.5 mm±0.6 mm to 13.06 mm±1.37 mm in control group.The radiographic analysis demonstrated scoliosis of 11.75°±2.87° in T₈-T₁₀ tethered segments,as compared with 0.94°±0.86° in the control group(P<0.001).Similarly,thoracic lordosis developed in the tethered segments-5.25°±6.21°,as compared to 4.25°±0.71° at the control levels(P=0.003).Conclusion The asymmetrical tethering performed by transpedicle screws with Nd-Fe-Bmagnets upon the vertebral body T₈-T₁₀ of mini-pigs can modulate their spinal growth and create the mild scoliosis in coronal section and lordosis in sagittal section.the magnitude range of magnetic force upon spinal growth plates is from 1.0 Nto 2.3 N.This method validate the hypothesis of spinal growth imbalance related scoliosis pathology and abide by the Hueter-Volkmann law.The asymmetrical posterior tethering of spine have an important role in scoliotic onset and progressing,lordosis in the sagittal section may be the primary deformity of scoliosis.

Key words: experimental scoliosis, spinal posterior tether, growth modulation, etiology, pathogenesis