The sacroiliac joints: evaluation using nuclear scintigraphy. Part 1: The normal horse

Area of Science:

• Veterinary diagnostic imaging
• Equine orthopedics

Background:

• Sacroiliac (SI) disease is a known cause of poor hindlimb function in horses.
• Accurate differential diagnosis for SI disease can be challenging.

Purpose of the Study:

• To establish baseline radiopharmaceutical uptake (RU) ratios in the SI region of clinically normal horses.
• To determine if these ratios differ between anatomical landmarks (L5 vertebra, tuber sacrale, SI joints).
• To investigate the influence of age and symmetry on these uptake ratios.

Main Methods:

• Analysis of dorsal scintigraphic images from 40 clinically normal horses (age 3-16 years).
• Comparison of motion-corrected and non-motion-corrected images.
• Quantification of RU using regions of interest and profile analysis.
• Superimposition of scintigraphic images onto radiographic pelvic images for anatomical reference.

Main Results:

• Tubera sacrale appeared as distinct oval regions with characteristic RU.
• Significant differences in RU were observed between the tuber sacrale (TS), SI joints, and the fifth lumbar vertebra (L5).
• Radiopharmaceutical uptake in the tubera sacrale decreased with increasing age, but SI joint uptake and gender did not significantly affect RU.
• High left-right symmetry was noted in the TS and SI joint regions of normal horses.

Conclusions:

• Scintigraphic images of horses with suspected SI joint disease should be interpreted alongside age-matched normal controls.
• A high degree of bilateral symmetry in radiopharmaceutical uptake is characteristic of normal equine SI regions.
• Marked left-right asymmetry in uptake is a potential indicator of abnormality.