#sesamoid bones

[moltenmasochrist]

Rib massage + diaphragm stretches have the local witches suspicious of where my limber youthfulness comes from.

[thescienceofequus]

Such injuries can be difficult to repair and even fatal; here's how to prevent sesamoid injuries.

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Two little bones sitting at the back of the fetlock both amaze and confound veterinarians. The sesamoids, as they’re called, anchor the suspensory apparatus that allows a horse’s foot and fetlock to move properly. Yet their location and anatomy make them vulnerable to injuries that can be difficult to repair and even catastrophic.

Given the sesamoids’ location, it isn’t surprising that high speeds can lead to fractures and soft tissue injuries. In a racehorse, for example, the fetlock can sometimes extend to the point that the sesamoid bones actually make contact with the ground. If the pressure is too great, those bones can shatter to a point that requires euthanasia.

“Horses have two proximal sesamoid bones on each limb,” says Jeff Blea, DVM, racetrack practitioner and current American Association of Equine Practitioners president. “They, together with the cannon bone and long pastern, make up the fetlock joint.” 

Blea explains that the sesamoids are surrounded by an intricate system of ligaments. The suspensory ligament begins at the top back of the cannon bone, runs down the cannon bone, and splits into two branches—one attaching to each sesamoid. Other ligaments connect the sesamoids to each other, and the distal sesamoidean ligaments extend down to the pastern bones. “If you look at it from a physiological standpoint, it’s a highly mechanical area,” says Blea. “It’s an area that is susceptible to increased tension, increased force, and increased pressure.”

While the sesamoids’ anatomy might make them seem like an accident waiting to happen, Emma Adam, Dipl. ACVIM, ACVS, a University of Kentucky researcher and former assistant to champion racehorse trainer Sir Michael Stoute, points out the remarkable way the bones facilitate a horse’s movement.

“Our patella is a sesamoid bone,” she says. “It is gliding over this amazing structure called our knee. In horses, the sesamoids provide a groove for these immensely strong flexor tendons, and they also provide mechanical support for this incredible unidirectional joint that sits in front of them. And they do both at the same time.”

Sesamoid bones are small—about the size of a walnut—and somewhat pyramidal in shape. That alone makes it difficult for surgeons or the body itself to repair a fracture. But Adam notes other challenges.

“Sesamoid bones have a really hard time,” she says, “because they don’t have the blood supply that many other bones do, they don’t have any musculature around them that can lend blood supply, and they don’t have a periosteum (the soft, protective tissue covering bone).”

Both blood supply and periosteum help bones heal. So without them the sesamoids are basically left to their own devices.

Read the rest HERE.

Types of sesamoid fractures: 

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Radiograph of a sesamoid fracture:

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[vladyoshi]

Sesamoid Bones, Harajuku by tokyofashion on Flickr.

[tokyo-fashion]

Girl in "Sesamoid Bones" jacket on the Harajuku Bridge, circa 2008.