Positron emission tomography using 18F-fluorodeoxyglucose reveals digital perfusion deficits associated with continuous weight-bearing in healthy standing horses.

Overview

• This study used PET imaging with 18F-fluorodeoxyglucose (18F-FDG) to assess blood flow patterns in the feet of healthy horses while standing still and after moving.
• The research identified specific areas in the feet where blood flow was reduced during continuous weight-bearing, but these deficits resolved when the horses were allowed to move.

Purpose of the Study

• To characterize how blood perfusion (blood flow) in the horse’s foot behaves under static weight-bearing conditions by using 18F-FDG PET scans.
• To compare perfusion patterns between continuous standing (weight-bearing), post-ambulation, and control conditions with ambulation before scanning.

Methodology

• Subjects: 8 healthy adult light-breed horses were evaluated between May 2021 and September 2024.
• Procedure:
  • Injected 18F-FDG during continuous weight-bearing standing (CWB) for 20 minutes while scanning.
  • Performed a repeat PET scan after the horses walked for 20 minutes (rescan).
  • On a different occasion, performed control scans where horses ambulated before the injection and scanning (Amb_Control).
• Analysis:
  • Quantified 18F-FDG uptake by measuring metabolic volume and standardized uptake values (SUV) at three foot locations: coronary band, lamellae, and sole.
  • Used Friedman statistical analyses to compare uptake across different conditions.

Key Findings

• Continuous weight-bearing scans revealed discrete, localized deficits in 18F-FDG uptake mainly in the medial regions of the sole and quarter lamellae (almost all horses showed these deficits).
• Quantitative measures showed:
  • Lower median metabolic volumes in the medial sole and medial lamellae during continuous weight-bearing compared to Amb_Control.
  • Reduced mean standardized uptake values in the lamellae under continuous weight-bearing conditions versus Amb_Control.
• The regions without FDG uptake (perfusion deficits) mostly improved after the horses ambulated (partial resolution in rescans).
• Perfusion deficits were not present when ambulation occurred before scanning, reinforcing the link between static weight-bearing and localized blood flow reduction.

Interpretation and Implications

• Static weight-bearing causes transient, localized decreases in blood perfusion in specific parts of the healthy horse’s foot, which are detectable using PET imaging.
• The variability in size and location of these perfusion deficits among individual horses suggests a natural variation in blood flow patterns under load.
• The complete or partial resolution of deficits after walking indicates that movement restores normal perfusion.
• These findings suggest a possible connection between prolonged weight-bearing-related hypoperfusion and the development of supporting-limb laminitis—a common painful and damaging condition affecting horse feet—warranting future clinical studies.

Concluding Remarks

• The study provided novel insights into the dynamic perfusion patterns of the equine foot under different loading conditions using PET and 18F-FDG.
• This imaging approach could be a valuable research and diagnostic tool for investigating the pathophysiology of foot diseases related to weight-bearing and vascular compromise in horses.