Spinal Cord Intramedullary Pressure in Thoracic Scoliotic Deformity

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In Brief Study Design. In vitro cadaveric study of thoracic spinal cord intramedullary pressure (IMP) in scoliotic deformity. Objective. To define the relationship between thoracic scoliotic deformity and spinal cord IMP. Summary of Background Data. Clinical studies of patients with thoracic scoliosis without other spinal pathology (spinal stenosis, etc.) have rarely reported an associated thoracic myelopathy. Previous clinical and cadaveric studies of kyphosis have reported associated myelopathy and increased spinal cord IMP. We sought to determine if IMP changes in response to main thoracic scoliotic deformity. Methods. In 6 fresh-frozen cadavers, a progressive main thoracic scoliotic deformity was created. Cadavers were positioned sitting with physiological spinal alignment, head stabilized using a skull clamp and spine segmentally instrumented from occiput to L3. The T3–T4 ligamentum flavum was removed, dura opened, and 3 pressure sensors were advanced caudally to T4–T5, T7–T8, and T10–T11 within the cord parenchyma. A step-wise main thoracic scoliotic deformity was then induced by sequentially releasing and retightening the skull clamp while coronally bending, concavity compressing, and convexity distracting posterior segmental instrumentation, allowing closure of lateral segmental osteotomies. After each step, fluoroscopic images and pressure measurements were obtained; the T4–T11 coronal Cobb angle was measured. Results. Induction of main thoracic scoliosis did not significantly increase IMP. The mean main thoracic maximal scoliotic deformity created was 77° ± 2° (range: 71°–84°). At maximal deformity, the mean [INCREMENT]IMP at T4–T5, T7–T8, T10–T11 was 2.2 ± 1.9 mm Hg, 1.0 ± 0.7 mm Hg, and 1.0 ± 0.8 mm Hg, respectively. Conclusion. In this cadaveric study, main thoracic scoliotic deformity did not significantly increase thoracic IMP. This correlates with clinical presentation such that clinical studies of patients with thoracic scoliosis without other spinal pathology have rarely reported an associated thoracic myelopathy with the thoracic scoliosis. This study helps explain the relative absence of myelopathy in isolated main thoracic coronal plane deformity. Level of Evidence: 5 Spinal cord intramedullary pressure was measured in an in vitro cadaveric model of thoracic scoliotic deformity. Thoracic scoliotic deformity did not significantly increase intramedullary pressure. This corroborates clinical studies of thoracic scoliosis without other spinal pathology rarely reporting an associated thoracic myelopathy with an isolated thoracic scoliosis.

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