419 - Pediatric Thoracic Volume Modeling for Early Onset Scoliosis: A Valida...

#419 Pediatric Thoracic Volume Modeling for Early Onset Scoliosis: A Validation Study

Cutting Edge Innovations/Non-conventional Therapies

Poster Presented by: J. Sembrano

Author(s):

K. England (1)
D. Polly (1)
C. Ledonio (1)
J. Sembrano (1)
B. Akbarnia (2,3)
E. Hoggard (4)

(1) University of Minnesota, Orthopaedic Surgery, Minneapolis, MN, United States
(2) University of California, Orthopaedic Surgery, San Diego, CA, United States
(3) San Diego Center for Spinal Disorders, La Jolla, CA, United States
(4) University of Minnesota, Radiology, Minneapolis, MN, United States

Abstract

Introduction: Early onset scoliosis (EOS) has a well-known association with decreased thoracic and subsequently lung volume. Virtual thoracic volume modeling from plain radiographs has been used in the adolescent idiopathic scoliosis (AIS) population. This correlates within 3% of thoracic volume from CT scans. For AIS patients with poor pulmonary function, the modeled 2 year post-op thoracic volume change is strongly correlated with the two year post-op pulmonary function test. However, this modeling was performed in an older, nearly skeletally mature population. The objective of our current research was to validate the use of the virtual radiograph to actual CT model to accurately predict lung volume in EOS patients. This virtual modeling using plain radiographs can be used to follow young children who undergo serial lengthening procedures, rather than exposing them to multiple high dose radiation CT scans over the course of their treatment.

Methods: A retrospective case study of children 10 years and younger with a diagnosis of early onset idiopathic scoliosis were identified at our institution. Those with congenital anomalies and/ or no CT scans were excluded. A convenience sample of three patients was chosen for this validation. Coronal and sagittal radiographs were used to model thoracic volume using Blender software to create the three-dimensional thorax, and Mini Magics to calculate the volume of the thoracic cavity. Lung and mediastinal volumes were calculated by independent Radiologists from the original CT scan using Voxar software. Using the CT-based volume as the gold standard, percent error was calculated by subtracting virtual volume from CT-based volume, and dividing by CT-based volume, see Figure 1A-E.

Results: One male and two female patients with EOS and an average age of 4 years (range 2y 10mo- 5y 7mo). Demographic data and calculated volumes are summarized in Figure 1F. Subject 1 had 1.6% error, subject 2 8.3% error, and subject 3 2.2% error. This averaged to 4% error.

Conclusion: The virtual model created to predict lung volume, previously proven in AIS and correlated with pulmonary function, is also accurate in young (< 10 years old) patients with EOS. Variability in error was noted and likely attributed to magnitude of curve and vertebral wedging, as well as rib deformation, which is a limitation in the current model. With an average 4% error of the volume measured by the virtual model versus radiation-heavy imaging modalities, thoracic volume modeling is a valid method to analyze lung volume for EOS patients, past and present.

Figure 1