Size of the C7-T1 articular processes is overestimated on lateral radiographs when compared to standing cone beam computed tomography.

Overview

• This study compared measurements of the size of the articular processes (APs) at the C7-T1 vertebral junction in horses using lateral radiographs versus standing cone beam computed tomography (CBCT).
• The research found that lateral radiographs tend to overestimate the size of the APs at C7-T1 compared to CBCT, which may affect the diagnosis of osteoarthritis (OA) in this region.

Background

• Radiography of the caudal cervical vertebral column is commonly used to examine horses for spinal issues.
• However, several factors can distort radiographic images, including:
  • Scapular superimposition (overlapping bones in the image)
  • Divergent X-ray beams causing magnification artifacts
  • Variations in the distance between the anatomical structures and the image detector
• These factors may make the articular processes (APs)—the joints that connect vertebrae—appear larger than they actually are, especially at the junction between the seventh cervical (C7) and first thoracic (T1) vertebrae.

Objective

• To assess whether lateral radiographs overestimate the size of the C7-T1 articular processes when compared to CBCT, which serves as a more accurate imaging standard.
• To examine the agreement between observers in measuring AP sizes and in grading osteoarthritis (OA) severity using radiographs versus CBCT.
• To investigate if measurement of AP height correlates with subjective OA grades on each imaging modality.

Methods

• Study Design: Retrospective comparison between two imaging techniques in horses.
• Data Collection:
  • 94 horses imaged between 2021 and 2023 with both lateral radiographs and standing CBCT scans focused on vertebrae C6-C7 and C7-T1.
  • A single observer measured AP size and vertebral body (VB) height ratios across the full dataset.
  • A subset of 15 cases was randomly selected for measurement by two observers to test reliability and agreement.
  • Osteoarthritis was graded subjectively on both imaging methods in this subset.
• Measurements:
  • AP:VB Height Ratio was used, which compares the height of the articular process to the height of the vertebral body, to standardize measurements and assess enlargement.
• Statistical Analysis:
  • Tests used included Shapiro-Wilk for normality, Student’s t-test, Wilcoxon Rank Sum test for group comparisons, and ordinal regression for OA grade correlations.
  • Intraobserver (same observer over time) and interobserver (between different observers) agreement assessed by intraclass correlation coefficients (ICC).

Results

• C7-T1 Measurements:
  • AP:VB ratios were significantly higher on lateral radiographs (mean 1.15) compared to CBCT (mean 1.08), indicating overestimation by radiographs (p = 0.002).
  • No significant difference was found in measurements at the C6-C7 level between imaging modalities.
• Observer Agreement:
  • Intraobserver reliability was good to excellent on both imaging methods, showing consistent measurements by the same observer.
  • Interobserver agreement was moderate on radiographs, suggesting some variability in measurements between different observers.
  • Interobserver agreement was excellent on CBCT, indicating CBCT is more reliable and consistent between observers.
• Correlation with Osteoarthritis Grades:
  • On CBCT, larger AP heights at C7-T1 correlated strongly with higher OA grades, implying accurate identification of disease severity.
  • No significant correlation between AP size and OA grade was found using radiographs, suggesting less reliability for OA assessment.

Conclusions

• Lateral radiographs tend to overestimate the size of the articular processes at C7-T1 compared to CBCT, potentially leading to false diagnoses or misinterpretation of OA severity.
• This overestimation was not seen at the C6-C7 vertebral level, indicating the effect is specific to the C7-T1 region.
• CBCT provides more accurate and reliable measurements that correlate better with osteoarthritis grading.
• Clinicians should be cautious when interpreting radiographic images of the C7-T1 articular processes, especially for diagnosing or grading osteoarthritis.