Concurrent radiological and ultrasonographical findings in the forelimb proximal sesamoid bones and adjacent suspensory ligament branches in yearling and 2-year-old Thoroughbred sales horses.

Background: Changes in the proximal sesamoid bones (sesamoids) and the insertional region of the adjacent suspensory ligament branch (branch) are of particular importance in young Thoroughbreds sold at public auction. Little is known about the prevalence of concurrent ultrasonographical branch change, relative to the various grades of radiological sesamoid appearance.

Objective: To examine the existence of concurrent radiological and ultrasonographical findings in individual sesamoid-branch units in sales horses; to determine whether there are any radiological findings that are consistently accompanied by a particular degree of insertional branch change, and to provide practical recommendations as to when suspensory branch ultrasonography may be warranted in a sales environment.

Study Design: Prospective cohort study using an enrolled sample.

Methods: Horses were enrolled with consignor permission from a large Thoroughbred yearling sale and five 2-year-old Thoroughbred sales the following year. Data from the radiological evaluation of forelimb sesamoids and the ultrasonographical examination of the adjacent forelimb suspensory branches were described.

Results: A total of 2204 yearling forelimb sesamoid-branch units and 1336 2-year-old forelimb sesamoid-branch units were included, from 551 sales yearlings and 334 sales 2-year-olds. The proportion of yearling sesamoids with grade ≤1 vascular channels that had adjacent grade ≥2 fibrillar branch change was 1.2%. The same proportion for 2-year-olds was 3.8%, with medial forelimb sesamoids with grade 1 vascular channels overrepresented in 2-year-olds in this category. In yearlings, 31% of sesamoids with grade 2 vascular channels had adjacent grade ≥2 fibrillar branch change and 59% of sesamoids with grade 3 vascular channels had adjacent grade ≥2 fibrillar branch change. In 2-year-olds, 47% of sesamoids with grade 2 vascular channels had adjacent grade ≥2 fibrillar branch change and 67% of sesamoids with grade 3 vascular channels had the same. Only one yearling sesamoid and one 2-year-old sesamoid with radiological abaxial concavity had grade ≥2 fibrillar branch change.

Main Limitations: Hindlimbs were not included. Clinical examinations were not performed and the status of any past or present inflammatory process at the sesamoid-branch enthesis could not be inferred from radiographs and ultrasonographic images alone.

Conclusions: The existence and prevalence of concurrent radiological and ultrasonographical findings in the proximal sesamoid bones and adjacent suspensory ligament branches in yearling and 2-year-old Thoroughbred sales horses has been established. General recommendations have been made for selective branch ultrasonography on the basis of radiological sesamoid appearance. The results support a separate aetiology for radiological sesamoid abaxial concavity that does not primarily involve the suspensory branch insertion.