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Standing lateral radiographic positioning does not represent customary standing balance.
Michelle C Marks1, Christian F Stanford, Andrew T Mahar
1Children's Hospital, San Diego, CA, USA.
Spine
|June 5, 2003
Summary
Radiographic measurement of sagittal spinal balance using the sagittal vertical axis (SVA) may not accurately reflect functional standing posture. Shoulder flexion during radiography shifts SVA posteriorly, compromising spinal alignment assessment.
Area of Science:
- Spine biomechanics
- Radiographic analysis
- Biomedical engineering
Background:
- Sagittal vertical axis (SVA) is a key measure for spinal alignment.
- Current methods for SVA measurement may be inaccurate in functional positions due to arm elevation.
- Quantifying error in radiographic SVA measurement is crucial for clinical interpretation.
Purpose of the Study:
- To assess the validity and reliability of SVA measurements in various standing positions.
- To compare SVA in functional versus radiographic positions.
- To determine the potential error in radiographic SVA measurements.
Main Methods:
- Utilized motion capture and radiography on 15 healthy female adolescents.
- Measured SVA using reflective markers on C7 and S1 spinous processes.
- Analyzed SVA during relaxed standing, gait, and positions with shoulder/knee flexion.
Main Results:
- Functional positions showed positive SVA (0.9-4.5 cm), while shoulder flexion yielded negative SVA (-4.6 cm).
- Shoulder flexion alone demonstrated good intertrial and intratrial reliability.
- Knee flexion increased variability; no radiographic position replicated functional spinal balance.
Conclusions:
- Radiographic SVA with shoulder flexion is significantly more posterior (3-4 cm) than functional SVA.
- Intertrial variability due to repositioning is approximately 0.8 cm.
- Shoulder flexion is the most reliable radiographic position, but does not replicate true spinal balance.