Proximal Sesamoid Bones

This information will help you as a breeder, owner, or trainer understand better the area of the sesamoids, how they can be injured, and how they can be treated.

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The athletic horse is a resilient, yet vulnerable animal. When racing, jumping, or competing at other sports that require speed, equine athletes are at increased risk of injury. While great strides have been made in preventing these injuries by learning more about exercise physiology, training, and bone formation, there still are instances when an athlete becomes injured and has to be treated. Because of this, researchers and veterinarians have studied why and how equine athletes get injured, and what the best courses of treatment are for various injuries.

Following is information on one area of the competitive horse that has shown a propensity for injury in athletes competing at speed, especially Thoroughbred and Standardbred racehorses–the sesamoids. This information will help you as a breeder, owner, or trainer understand better the area of the sesamoids, how they can be injured, and how they can be treated.


The stay apparatus consists of ligaments, tendons, and muscles, and enables the horse to sleep in an standing position by stabilizing the joints of the forelimb and hindlimb. The suspensory apparatus, a portion of the stay apparatus in the lower limb, is a ligament that extends from the top of the cannon bone to the first (long) and second (short) phalanx (pastern) of the lower limb. The suspensory apparatus consists of the suspensory ligament, the sesamoid bones, and the distal sesamoidean ligaments, and is located in front of the flexor tendons and behind the cannon bone. The sesamoid bones of the lower limbs consist of the paired proximal sesamoid bones that are embedded within the suspensory ligament, and the distal sesamoid (navicular) bone that is contained within the hoof capsule. The proximal sesamoid bones are roughly triangular in shape, with the proximal most portion acting as a point of insertion for the suspensory ligament, and the base acting as a point of origin for the distal sesamoidean ligaments. The intersesamoidean ligament is a dense ligament that firmly secures the proximal sesamoid bones together along their axial aspect. The sesamoid bones provide stability to the suspensory apparatus as it courses around the back of the fetlock joint, and they function to prevent extreme overextension of the fetlock joint when the horse is performing

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Written by:

John G. Peloso, DVM, MS, Dipl. ACVS, is owner and surgeon of Equine Medical Center of Ocala in Fla.

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