Abstract
Introduction
Scheuermann's kyphosis is a primary sagittal plane deformity that manifests in adolescence. The wedged vertebrae cause increased thoracic kyphosis and a foreshortened thoracic length. The effect on the thoracic volume has been less well studied. With the ability to accurately model thoracic volumes, we are now capable of virtually modeling the effect of increasing kyphosis on thoracic volume. Virtual modeling may allow us to determine the point of diminishing returns in deformity correction when trying to improve pulmonary status. We hypothesize the computed thoracic volume measured from a 3D virtual model decreases with progression of kyphosis from 50 to 100 degrees.
Methods
Blender software was used to create a threedimensional thorax model with normal coronal and sagittal balance. Virtual wedging of vertebral bodies was performed for the model to be progressively deformed by 10 degrees from 50100 degrees of kyphosis. Thoracic volume was calculated via shrinkwrap modifier applied to an uvsphere within the thoracic cavity.
Results
Virtual wedging of vertebral bodies was necessary to achieve virtual progression of sagittal curve. As kyphotic angle increased, more vertebral segments had to be wedged (>5 degrees). Thoracic volume in the virtual adult thorax with a 50degree kyphosis was 1679cc. This volume decreased in a linear fashion by a mean of 5.4% for every 10 degrees more of kyphosis. The final volume was 1218cc at 100 degrees of kyphosis, which was a 27% decrease in volume from baseline.
Conclusion
As the deformity progresses from 50 to 100 degrees there is a 27% decrease in the thoracic volume. The decrease appears linear. While there is not a direct relationship between thoracic volume and pulmonary functions, adequate thoracic volume is necessary for adequate pulmonary function. This study helps to establish the relative magnitude of volume decrease based upon the sagittal Cobb angle.