Authors: Adam Kundishora, MD
Pedicle asymmetry in idiopathic scoliosis (IS) has been poorly assessed due to current limitations in 2D measurement techniques and disregard for differences in overall patient size, leading to unreliable findings. Prior studies also fail to analyze curve metrics that best predict asymmetry. We sought to characterize metrics that predict pedicle differences using normalized data and 3D computer-aided (CAD) software.Methods: IS patients underwent x-rays and CT for patient-specific template creation with the Firefly system. Curves were characterized on x-ray. CTs were rendered in novel 3D CAD software allowing for vertebral body rotation (VBR) to be measured against historically difficult to define anatomical reference planes. Concave (CC) pedicle measurements were normalized to convex (CV) and expressed as percent change. Pedicle differences were analyzed with paired t-test. Simple linear regression was calculated to assess their relationships to curve magnitude, VBR, and deformity angular ratio (DAR).
322 pedicles from 14 patients were analyzed. Proximal thoracic (PT) and main thoracic (MT) CC pedicles had decreased width (PT: p=0.001; MT: p < 0.0001) and cross-sectional area (PT: p=0.009; MT: p < 0.0001). Thoracolumbar/Lumbar (TL/L) CC pedicles had increased length (p=0.004). Larger differences were observed at apical pedicles and this diminished with distance from apex. Simple linear regression found decrease in PT CC pedicle width (W) and area (A) with increased curve magnitude (W: p < 0.007; A: p < 0.001) and increased DAR (W: p < 0.04, A: p < 0.01), decreased MT pedicle area with increased VBR (p=0.049), and increased TL/L pedicle length with increased curve magnitude (p=0.006).
Compared to their CV counterparts, CC pedicles in PT and MT curves have decreased width and cross-sectional area; conversely CC pedicles in TL/L curves are longer. Differences correlate with increased curve magnitude and DAR in PT and TL/L curves but with increased VBR in MT curves.