| Background:Idiopathic Scoliosis (IS) is one of the most common deformities of spine in adolescent. The etiology of Idiopathic Scoliosis is not yet clear. Many researches indicate that the asymmetric load from an erect posture plays an important role in the development of scoliosis. The vertebral endplate is formed by epiphyseal ossification of the vertebral body. It plays an important role in the growth of vertebral body and the nutrition of intervertebral disc. Abnormal mechanical loading appears in scoliosis as compared with normal spines. How vertebral endplate was changed in scoliosis is not well understood.In order to study spinal deformity and test novel treatments for scoliosis, many scoliosis models have been developed in recent years. Most of them apply mechanical tethering techniques to create an asymmetric load. These tethering techniques are considered the most reliable approaches for generating animal models for spinal deformity; however, there are complications with these models. The development of the deformity depends on the growth potential and the spinal curve then progresses slowly. When severe scoliosis develops, these models are unable to reserve sufficient growth potential for experiments. An optimal tethering scoliosis model should develop lumbar scoliosis in a short time, and the tethering technique could be a potential surgical surgery for scoliosis.Objectives:To reconstruct the3-dimensional(3D) models of vertebral endplate and internal canal structure based upon the micro computed tomography(MicroCT) scanning data and clarify the structural characteristics and changes of bone, canals and lumbar vertebral endplate with advancing age in SD rats. To develop an asymmetric force scoliosis rat model by using nickel-titanium coil spring (NT coil spring) and observe the spinal growth modulation with the asymmetric load. Determine the vertebral endplate changes at asymmetric loads scoliosis rat models by micro-CT to further reveal the formation mechanism of scoliosis.Methods:Lumbar spines from male SD rats aged3,9and16months (n=15each) were subjected to MicroCT scan. Mimics software was used to reconstruct3-dimensional (3D) models of the lumbar vertebral endplate and the internal canal structure. The bone volume fraction (BV/TV) of endplate was measured by CTAn software.Scoliosis was induced in fifty-five5-week-old female SD rats using a nickel-titanium (NT) coil spring. Two bone screws were implanted in vertebral bodies via the roots of right transverse processes of L2and L5. The two ends of nickel-titanium (NT) coil spring attach to L2and L5screws. The experimental rats were randomly divided into two groups:In Group A (n=15), the NT coil spring was not removed until these rats reached physical maturity (age,12weeks). We conducted a micro-CT analysis of the vertebral endplate at the curve apex in rat lumbar scoliosis models, and the3D models of the endplate bone structure and the internal canal structure were reconstructed by ’Mimics’. The vertebral epiphysis and intervertebral disc of the curve apex were evaluated from histology. Group B (n=40) was further randomly subdivided into five subgroups (n=8for each subgroup):removal of the spring after1week (Group B1),2weeks (Group B2),3weeks (Group B3),4weeks (Group B4), and5weeks (Group B5). All rats were followed for a7-week period with serial radiographs to document change of the deformity.Results:The rebuilt3D models of vertebral endplate showed that the SD rat lumbar endplate was a thin layer of bone and the canals within the vertebral endplate formed a ring-shaped canal network after reconstruction. Communicating branches existed between the adjacent canals. Every ring-shaped canal connected with trunk canals lying in the ventral and dorsal portions of the endplate. The BV/TV of the endplate in the ventral portion was lower than that in dorsal portion (the ventral side:79.9±7.3%, the dorsal side:90.6±6.2%, P<0.05) and the BV/TV increased with advancing age.All experimental animals of Group A developed progressive, structural scoliotic curves convex to the left in the lumbar segment. The average initial coronal Cobb angle was25.7±2.4°immediately after the operation and progressed to61.5±5.4°on average over7weeks. The L3and L4vertebrae were wedging to the tether side. The rebuilt3D models show that the concave side of the scoliotic endplate is thinner than the convex side, the canals are sparsely, and the BV/TV significantly increased. In Group B, the deformity of the lumbar progressed after the spring load was applied and regressed after the spring was removed. The scoliosis in Group B1-B3(the spring removed before sexual maturity) regressed after spring removal until the rats reached sexual maturity (4weeks after spring implant surgery). The scoliosis in Group B4-B5(the spring removed after sexual maturity) regressed only during the first week after spring removal surgery. The average coronal Cobb angle was7.8±1.3°(range:6.0-10.2°) in Group Bl at the final follow-up and there was only one experimental rat that maintained a curve>10°. The models of Group B2-B5maintained stable scoliotic curves (coronal Cobb angle of L2-L5>10°) convex to the left in the lumbar segment at the final follow-up. The reduction in the degree of scoliosis immediately after spring removal surgery showed that the lumbar lordoscoliotic curves in this study are not rigid and the flexibility decreased with the prolongation of tethering.Conclusions:The canals within the rat lumbar vertebral endplate are not haphazard, but regularly arrayed to form a ring-shaped network of many circular canals, communicating branches and ventral and dorsal trunk canals. This canal network provides channels for blood vessels within the endplate. The ratio of the older rat canals decreased in endplate.This study established a rat lumbar scoliosis model in a short time and verified that the asymmetric load can modulate spinal growth and result in scoliosis. The lumbar lordoscoliotic curves in this study are not rigid and the flexibility decreased with the prolongation of tethering. The lumbar asymmetric load causes concave side of the vertebral endplates tends to form a thin dense bony plate. Such pathological changes may adversely affect growth of concave side of the vertebrae and the intervertebral disc nutrition. |
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