Catastrophic distal sesamoidean ligament rupture in 72 racehorses in California

Rupture of major distal sesamoidean ligaments (DSLs) in racehorses results in suspensory apparatus failure. Our objective was to describe postmortem findings and exercise histories for Thoroughbred (TB) and Quarter Horse racehorses that had DSL rupture as the sole cause of catastrophic musculoskeletal and suspensory apparatus failure. We described horse signalment, activity at the time of injury, and postmortem findings and compared the exercise histories with those of event-matched control horses. In 72 racehorses, predominantly ≥4-y-old, catastrophic rupture of forelimb DSLs (41 left, 29 right, 2 bilateral) occurred while racing (61), training (9), or during non-exercise activity (2). DSL rupture occurred in isolation in 27 horses; the remaining 45 horses also had disruption of other ligaments and tendons secondary to associated fetlock or pastern disarticulation. Rupture of the DSLs involved the straight (69), oblique (68 medial, 69 lateral), cruciate (49), and short (49) DSLs. Complete rupture of the straight, oblique, cruciate, and short DSLs occurred more frequently ( p  < 0.05) in the proximal third of the pastern region (49 horses) than complete rupture of the straight and oblique DSLs in the distal third of the pastern region (23 horses). Two horses had chronic desmopathy in the proximal third of the oblique DSL. Proximal ruptures occurred more frequently in the left forelimb ( p  = 0.005). TB horses with DSL rupture had longer careers, more time in layup, and less high-speed activity in the year before injury than unaffected control horses. Complete rupture of the DSLs had a very low prevalence (1.4%) among catastrophic musculoskeletal injuries.