Diagnostic Accuracy of Scintigraphy for Detecting Morphological Variation of the Sixth Cervical Vertebral Ventral Lamina in Horses: A Retrospective Study.

Overview

• This study evaluated the effectiveness of scintigraphy, a bone imaging technique, in detecting structural variations of the sixth cervical vertebra (C6) in horses, compared to standard radiography.
• The goal was to determine how well scintigraphy could identify abnormalities and to establish an optimal cutoff ratio for diagnosis.

Background

• Horses commonly exhibit morphological variations or transpositions in the ventral lamina of the C6 vertebra, which can impact their health and performance.
• Radiography is traditionally used to identify these bony variations due to its detailed anatomical imaging capabilities.
• Scintigraphy is a nuclear medicine technique that assesses bone metabolism and activity rather than just anatomy, providing functional information about bone health.
• Prior to this study, the diagnostic accuracy of scintigraphy for identifying C6 ventral laminar variations had not been established.

Study Design and Methods

• This was a retrospective, single-center study involving 34 horses who underwent both radiographic and scintigraphic examinations focusing on the C6 and adjacent C7 vertebrae.
• Radiography was used as the reference (gold) standard to categorize horses as either normal (22) or abnormal (12) based on the presence of C6/C7 ventral laminar anomalies.
• Among abnormalities, 5 horses had unilateral (one side) anomalies and 7 had bilateral (both sides) anomalies.
• Scintigraphic evaluation utilized a semiquantitative approach by calculating the ratio of radioactive uptake between C6 and C7 (C6:C7 uptake ratio), adjusting for background noise.
• Both a visual diagnostic assessment and quantitative receiver-operating characteristic (ROC) curve analysis were performed to evaluate sensitivity, specificity, and identify an optimal cutoff ratio.

Key Findings

• Visual scintigraphic assessment showed moderate diagnostic performance with:
  • 75.0% sensitivity — ability to correctly identify horses with anomalies.
  • 72.7% specificity — ability to correctly identify normal horses.
• Semiquantitative ROC analysis identified an optimal C6:C7 uptake ratio cutoff of 0.81:
  • This cutoff yielded 66.7% sensitivity and 81.8% specificity, balancing false positives and false negatives.
  • The area under the ROC curve (AUC) was 0.762, indicating moderate accuracy of this parameter in distinguishing abnormal from normal horses.
• Statistically significant differences were found in the C6:C7 uptake ratios between abnormal and normal horses on both sides:
  • Left side: abnormal horses had a mean ratio of 0.860 ± 0.149 (p=0.006).
  • Right side: abnormal horses had a mean ratio of 0.812 ± 0.148 (p=0.035).
• No significant side-to-side (left vs. right) differences in uptake ratio were detected within individual horses.

Interpretation and Implications

• Scintigraphy shows moderate effectiveness at detecting ventral laminar anomalies of the C6/C7 vertebrae, meaning it can be a useful diagnostic tool but is not definitive alone.
• The C6:C7 uptake ratio of 0.81 can potentially serve as a practical and quantifiable cutoff threshold for screening purposes.
• Due to limitations including sample size and retrospective design, further research with larger populations is needed to validate and potentially refine this cutoff and confirm scintigraphy’s diagnostic reliability.
• In clinical practice, scintigraphy could complement radiography by providing information about bone function and activity, enhancing detection and monitoring of vertebral anomalies in horses.

Limitations

• Retrospective, single-center study design may limit generalizability of results.
• Relatively small sample size, especially in the abnormal group, affects statistical power.
• Radiography, though a good anatomical reference, itself has some limitations in sensitivity for subtle bone variations.
• The study focused on C6 and C7 vertebrae only; results may not apply to other spinal regions or types of vertebral anomalies.

Conclusion

• Scintigraphy has moderate diagnostic accuracy for detecting morphological variations in the ventral lamina of the sixth cervical vertebra in horses.
• Using a semiquantitative C6:C7 uptake ratio cutoff of 0.81 provides a practical adjunct screening tool.
• Further prospective, larger-scale studies are warranted to establish scintigraphy’s definitive role and improve diagnostic protocols in equine spinal disease.