Objective: To describe scintigraphic and transrectal ultrasonographic anatomic variants of the lumbosacral (LS) articulation in horses and to determine the agreement between results obtained with each imaging modality.
Animals: 243 horses (81 Selle Français Warmbloods, 81 French Standardbred Trotters, and 81 Thoroughbreds).
Procedures: A retrospective search of clinical records was conducted to identify horses that had undergone nuclear scintigraphy and transrectal ultrasonography of the LS region of the vertebral column between January 2016 and December 2019. Scintigraphic images were evaluated by 2 observers blinded to the other's results for classification of LS articulation anatomic variants (scintigraphic type); intra- and interobserver agreement were determined. Ultrasonographic images were evaluated for classification of LS intervertebral symphysis anatomic variant (ultrasonographic grade) by 1 observer blinded to horses' identities and scintigraphic findings; agreement analysis was performed between scintigraphic type and ultrasonographic grade. Descriptive and statistical analyses were performed to describe distribution of anatomic variants.
Results: The scintigraphic classification system (scintigraphic type) had excellent intra- and interobserver agreement. Agreement between results for scintigraphic type and ultrasonographic grade was moderate (κ = 0.61; 95% CI, 0.52 to 0.70). Anatomic variants of the LS articulation were observed in all groups. The distribution of variants differed significantly among breeds but not sexes.
Clinical relevance: Anatomic variations of the LS articulation in horses must be known to avoid misinterpreting them as clinically meaningful findings. Further research is needed to determine potential relationships between these anatomic variants and LS lesions, their clinical manifestations, and their influence on athletic performance.