[In-vivo change of the spine canal after surgical corrections of severe and rigid kyphoscoliosis]

Objective: To measure the length changes of the spine canal of patients with severe kyphosis after treatments of deformity using osteotomy surgeries. Methods: Retrospectively investigated the data of 10 severe kyphosis patients who were treated between August of 2016 and December of 2018 at Beijing Chaoyang Hospital (5 with Ponte and 5 with posterior vertebra column resection (VCR) osteotomy surgeries). For each patient, the full-spine X-Ray images were used to measure Cobb angles before and after the surgery; 3D CT images were used to construct a 3D model of the spine, including the T(2) to L(2) vertebrae and the spine canal. The 3D model was then used to measure the spinal canal lengths (SCLs) between the upper and lower vertebrae (U/LEV) and between T(2)-L(2) vertebrae at 5 locations on the spine canal cross section (anterior, central, posterior, left and right locations), and the vertical distance between the T(2) and L(2) vertebrae before and after the surgery. The data were statistically analyzed using t tests. Results: For the 5 patients of Ponte osteotomy, the Cobb angles were improved by 89°±17°(56%±11%) and 84°±16°(56%±8%) in the coronal and sagittal planes respectively after the surgery. The changes of the SCL between the T(2)-L(2) vertebrae were (9.9±4.8) mm and (6.0±12.7) mm, and those were (7.2±5.4) mm and (-0.5±7.9) mm between the U/LEV, respectively at the concave and convex sides of the canal. The vertical distance between the T(2)-L(2) vertebrae increased by (66.1±12.0) mm. For the 5 patients with VCR osteotomy, the Cobb angles improved by 83°±19°(60%±10%) and 82°±22°(56%±10%) in the coronal and sagittal planes, respectively. The changes of the SCL between the T(2)-L(2) vertebrae were (-5.5±5.3) mm and (-14.0±6.6) mm, and those were (-8.3±8.4) mm and (-20.7±11.6) mm between the U/LEV, respectively at the concave and the convex sides of the canal. The vertical distance between the T(2)-L(2) vertebrae increased by (41.5±12.4) mm. Conclusions: The Ponte osteotomy significantly elongates the SCLs, especially at the concave side, and the VCR osteotomy shortens the spinal canal, resulting in significant compression of the spinal cord at the convex side.