Geometry, Growth, and Shape of the Normative Pediatric Thoracic and Lumbar Vertebrae and Ribs, and Comparisons with Adolescent Idiopathic Scoliosis

Growth of the thoracic and lumbar spines, and rib cage is a complex composite of the growth contributed by each individual vertebra and rib; however, the majority of literature describing growth of these structures report heights and lengths of the spine or volume of the ribcage. Previous pediatric studies focusing on the morphology of individual ribs and vertebrae use inconsistent measurement techniques to collect geometric dimensions from nonhomogeneous samples and few of these studies evaluate growth or possible vertebral level and sex-related differences in the pediatric morphology. Data detailing the normative morphology and growth of the spine and rib cage may provide insights into the progression of spinal deformities like adolescent idiopathic scoliosis (AIS). AIS is a complex three-dimensional (3D) deformity of the thoracic and lumbar spines and rib cage involving lateral bending of the spine, axial rotation of the vertebrae, wedging of the vertebral bodies, and malformation of the vertebral structures. Despite the large amount of subject specific variability present in AIS, classification schemes like the Lenke system have been developed to help categorize the scoliotic deformity and provide guidance for surgical interventions. Lenke-types 1, 2, and 5 collectively account for approximately 83 percent of AIS cases requiring surgery. The standard surgical treatment for AIS is mechanical de-rotation of the spine followed by posterior spinal fusion (PSF). In some cases deformity progression has been observed even after PSF suggesting that the vertebrae can continue to grow and develop following spine arthrodesis. New surgical treatments for AIS rely on modulating growth instead of arresting it; however these techniques require knowledge about how mechanical forces impact normative growth. Such investigations can be conducted in silico using finite element (FE) models. FE models of the spine have been used to investigate scoliotic deformity progression as well as correction using surgical constructs. While previous FE models of the spine have simulated axial growth of the vertebral bodies, growth of the posterior elements (pedicles, facets, and major processes) is largely ignored due to a lack of data describing their development. Such limitations need to be addressed if better models of progression and correction are to be created. This thesis provides a thorough analysis of the pediatric thoracic and lumbar vertebrae and rib morphology and growth collected from 3D reconstructions of computed tomography scans of 202 skeletally normal subjects between the ages of 1 and 19 years. This normative data is compared with preoperatively and postoperatively, two years following PSF, obtained 3D spine reconstructions of 36 Lenke-type 1, 2, and 5 subjects to quantitatively assess the deformity in each and evaluate vertebral remodeling following spine arthrodesis. Finally a method is developed to integrate the pediatric growth data for all vertebral structures into a growing FE model which is used to assess the impact of vertebral growth on a simulated PSF construct. In addition to improving FE models of the growing spine, the normative and Lenke-type-specific morphology data presented here can be used to optimize the timing and duration of growth modulating devices and develop novel techniques for the treatment of AIS.Ph.D., Biomedical Engineering -- Drexel University, 201