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- Even Normal Standing May Trigger Digital Ischemia in Horses—New PET Evidence
Even Normal Standing May Trigger Digital Ischemia in Horses—New PET Evidence
Am J Vet Res. 2025
Obi Veterinary Education
March 02, 2026
Georgia Skelton, DVM; Kate Wulster-Bills, VMD, DACVR; Sarah Ciamillo, DVM; Sergey Anishchenko, PhD, MC; Andrew van Eps, BVSc, PhD, DACVIM
Background
Supporting-limb laminitis is a serious complication associated with prolonged alterations in weight-bearing and ambulation, often following painful limb injuries. Although ischemia is suspected to play a central role in its pathophysiology, the precise mechanisms remain unclear. Prior evidence suggests that reduced ambulation, rather than increased weight-bearing load alone, may contribute to lamellar ischemia. While ambulation has been shown to increase digital uptake of 18F-fluorodeoxyglucose (18F-FDG), real-time perfusion patterns during continuous static weight-bearing have not been characterized. This study aimed to define healthy digital perfusion patterns under static load using 18F-FDG positron emission tomography (PET).
Methods
Eight systemically healthy adult light-breed horses underwent standing PET imaging of one randomly selected forelimb. For continuous weight-bearing (CWB) scans, 30 mCi 18F-FDG was injected at scan initiation, and horses remained standing immobile for 20 minutes. After 20 minutes of ambulation, a repeat scan (Amb_Rescan) was performed. On a separate occasion, an ambulatory control scan (Amb_Control) was conducted, allowing ambulation immediately following tracer injection prior to imaging. Scans were repeated to assess intra-individual repeatability. Regions of interest included the coronary band, lamellae, and sole, analyzed for metabolic volume and standardized uptake value (SUV). Comparisons between scan conditions were performed using Friedman analyses with post hoc testing.
Results
Discrete focal uptake deficits were observed during CWB scans, most consistently affecting the medial sole (8/8 horses) and medial lamellae (7/8 horses). These deficits were evident within the first five minutes following tracer injection and persisted throughout the 20-minute scan. Medial sole metabolic volume was reduced by approximately 34% during CWB compared with Amb_Control, and medial lamellar metabolic volume decreased by approximately 13%. Lamellar SUV mean values were approximately 16% lower during CWB relative to ambulatory conditions. Coronary band metabolic volume decreased by approximately 50% during CWB. Deficits partially resolved following 20 minutes of ambulation (Amb_Rescan) and were absent in Amb_Control scans. Deficit patterns were repeatable within individuals but varied between horses.
Limitations
Sedation with detomidine was required for all imaging sessions and may have influenced vascular tone; however, ambulatory control scans suggested that ambulation mitigated these effects. Differences in scan acquisition duration between CWB and ambulatory conditions may have influenced tracer distribution timing, although SUV normalization accounted for time. PET imaging required non–attenuation-corrected reconstruction, which could affect absolute SUV quantification. The small sample size and focus on healthy horses limit direct extrapolation to clinical laminitis cases.
Conclusions
In healthy horses, static continuous weight-bearing alone resulted in discrete, regionally localized perfusion deficits in the medial sole and lamellae, detectable using 18F-FDG PET. These deficits consistently resolved with ambulation. The findings suggest that time spent standing immobile, even under physiological load, may compromise regional digital perfusion and could contribute to susceptibility to supporting-limb laminitis. Further investigation is warranted to determine whether individual perfusion patterns predict laminitis risk and whether PET-guided interventions may improve preventive strategies.
Representative images from 3-D maximum-intensity projection reconstructions of CWB scans of 3 different horses scanned for 20 minutes while standing continuously still in the PET detector after injection of 18F-FDG. Images A and D are from the right front foot of a healthy Thoroughbred horse. The extensive outlined deficits (asterisks) are discrete areas devoid of 18F-FDG uptake in the medial digit, which include large areas of the medial coronary band, medial quarter lamellae, medial terminal papillae, and most of the medial sole. The associated medial circumflex vessels of both the sole and coronary band are also devoid of 18F-FDG uptake. Images B and E are from the right front foot of a healthy Standardbred horse with focal uptake deficits affecting the medial coronary band, medial quarter lamellae, and a large portion of the sole but not the terminal papillae or circumflex vessels. Images C and F are from the left front foot of another healthy Thoroughbred horse, demonstrating similar but smaller focal uptake deficits confined to the medial lamellae and sole. Images A and B are oriented obliquely in a dorsal-palmar, proximal-distal, medio-lateral direction; image C is oriented obliquely in a palmar-dorsal, proximal-distal, latero-medial direction. Images D, E, and F are oriented in a proximal-distal transverse view. Scan protocols are defined in Figure 1.
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