| Background: Adolescent idiopathic scoliosis (AIS) is one of the most commondeformities of the musculoskeletal system for young people. The incidence ranges from1%to3%. Spinal fusion is usually recommended for patient whose curve is greater than50°,and for those with curves between45°to25°, spinal bracing would be considered. However,the spinal fusion has several problems including restriction of the trunk height, limitation ofthe thoracic development and even compromise the pulmonary function. And the efficacyof bracing is not definite and could be compromised by poor compliances. Recently, thenon-fusion surgery for the treatment of immature scoliosis has been proposed, includinganterior vertebral staples and posterior growing rod. But the growing rod requires seriallengthening procedures before maturity and the anterior staples have to be put around majorvascular structures, both of which greatly increase the surgical risks and rate ofcomplications. We, therefore, propose a posterior only approach tethering procedure whichincludes implantation of an allograft tendon via the costo-transverse foramen. Our goal isthat this allograft tendon would be able to correct the spinal scoliosis by growth modulationwhile preserving the growth potential.Objectives:To investigate the feasibility and efficacy of spinal growth modulation and scoliosiscorrection with unilateral flexible tethering via the costo-transverse foramen on immatureporcine models, in addition, Micro-CT and histo-morphological analysis were done toillustrate the effects of tethering. On the other hand, based on the Chinese visible human(CVH) database and clinical radiology database of AIS, anatomical and radiological studywas done on the region of costo-transverse foramen and the pedicle-rib complex, whichfurther validated and supported the clinical application and feasibility of the tetheringprocedure. Methods:This IACUC-approved study included17eight weeks old immature Yorkshire pigs,which were randomized into four groups, including tendon tethering, sham operation,scoliosis treatment and scoliosis none treatment. In the initial study of tethering group andsham operation, scoliosis was induced using a previously harvested allograft tendoninserted as a tether into the costo-transverse foramen within the pedicle-rib complex.Afterwards, in the scoliosis treatment study, a first stage surgery was performed to initiate aspinal deformity by tethering the ribcage and spine. Serial radiographs were obtainedbi-weekly to confirm progression of spinal deformity. Once the animals had demonstrated aspinal deformity greater than45degrees, they underwent a second stage surgery of scoliosistreatment or sham treatment operations. For the treatment group a posterior convex sideallograft tendon tether was applied with a bone anchor in an effort to correct the deformityvia the costo-transvere foreman. For all four groups, the progression of deformity wasdocumented by monthly radiographs. Coronal, sagittal and axial changes were assessedusing the Cobb method, along with post mortem CT of the spines. In addition, Micro-CTand histo-morphological analysis were done to illustrate the effects of tendon tethering.Based on the CVH database, three dimensional model was generated to study theanatomical structures of costo-transverse foramen and the pedicle-rib complex. Parametersof the costo-transvere foramen and the pedicle rib-complex were measured as well. Thethree dimensional computered tomography(CT) data of104AIS patients(49males and75females, averaging10years old) who underwent CT examination in our institution fromJuly2005to March2013, and38matched normal people(15males and23females,averaging11years old) who underwent CT examination in our institution from May2007to December2012, were reviewed retrospectively to illustrate the morphologicalcharacteristics of the costo-transverse foramen and pedicle-rib complex. According to theLenke classification, there were58cases of Lenke I and46cases of Lenke III in the AISgroup. The average Cobb angles of the main thoraic curve was45.95degrees in the AISgroup. Based on the three dimensional reconstruction of CT data in Amira software, themorphological characteristics of the costo-transverse foramen and pedicle-rib complex indifferent levels were described and analyzed in both AIS and normal people. And comparisons were made within and between the AIS and normal people group. The possiblefactors contributing to the morphological changes in AIS patients were discussed andsummarized. In addition, the effects of posterior only spinal fusion surgery on immaturescoliosis spine were discussed in a clinical follow-up study.Results:The animals from tendon tethering and sham operation groups were observed for16weeks post-surgery. Significant three dimensional spinal deformities were induced in thetendon tethering group, compared to those of sham operation group. And the followingMicro-CT and histo-morphological analysis further illustrated the effects of the tether bythe demonstration of the changes within the vertebral trabecular and growth plates. In thescoliosis treatment study,12weeks after the second surgery, the deformities of thetreatment group were significantly smaller than those of none treatment group, and thescoliosis corrective and growth preserving effects of the tether were also interpreted by thefollowing Micro-CT and histo-morphological analysis. A three dimensional model of thecosto-transverse foramen and the pedicle-rib complex was generated. The anatomical studyproved that the pedicle-rib complex is a three dimensional structure, in whichcosto-transverse foramen is formed. The costo-transverse foramen varies among differentlevels, but all of them are large enough for tether placement. The sagittal effective diameterof the pedicle-rib complex is significantly smaller than that of the sagittal boundary of thecomplex. The safe zone within the pedicle-rib complex varies among levels, but theeffective ranges reached by approaches with the safe zones are consistent throughout alllevels. The cross sectional area of the costo-transverse foramen in AIS patients was largerthan those of normal matched people. The axial width of the pedicle-rib complex was largeron the concave side, and the pedicle was larger on the convex side. The axial width of thepedicle-rib complex on the concave side was smaller than that of normal matched people.The width of pedicle-rib complex of both groups were larger than those of pedicles, and allshowed the pattern of cranial to caudal decreasing. All patients were followed up for at least2years, the corrections were well maintained and there were no signs of crankshaft orrespiratory function defect.Conclusion: With the placement of a unilateral allograft tendon spinal tether via thecosto-transverse foreman, a significant spinal deformity can be produced on normal spine and a significant scoliosis can be corrected by applying this tethering procedure.Furthermore, the anatomical study of the costo-transverse foramen and the pedicle-ribcomplex of both normal and AIS population supported the clinical feasibility of theprocedure. These data suggest that an allograft tendon tethering approach may represent anovel fusion-less procedure to treat idiopathic scoliosis in immature population. |
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