Equine Leg Anatomy: Part One

Dr. Christie Ward, DVM, MVSc, PhD, presented on Equine Anatomy at the Leatherdale Equine Center at the U of M Trainer's Series.  She graciously gave me permission to share my notes and photos.  

Part One: Front Leg Anatomy

Limbs are primarily made up of bone, muscles, ligaments, and tendons. Limb muscles are primarily organized in functional pairs: one set flexes while the other set extends (i.e. biceps & triceps). Did you know that horses don't have muscles below the knee?  This lessens the weight of their limbs and contributes to speed and athleticism.

Ligaments connect bone to bone and passively restrict movement by stretching when loaded and recoiling, providing bounce. Tendons connect muscle to bone.  

A horse's front leg consists of: shoulder, elbow, radius, ulna, knee (comprised of carpal bones in 2 rows), cannon bone, splint bones (on either side of the cannon bone), and the bones of the fetlock, and foot.  

Did you know that horses don't have collarbones (aka clavicles)?  The entirety of the horse's forelimb has no bony attachment to their body and is held in place by a sling mechanism of muscles. This is one reason why horses can measure different heights at different times.  For instance, when excited with muscles tensed, horses can actually be 3 inches taller than when relaxed!

The horse's splint bone don't bear weight directly, but they do provide a surface for the carpal bones of the knee.  They typically fuse to the cannon bone fairly early in the horse's life.  When young horses "pop a splint," it is usually on the inside of the front cannon bones.  This can occur when a young uncoordinated horse whacks itself, working on hard surfaces, or in small circles.

Bucked Shins

Another bone injury young horses (especially racehorses) are prone to are "bucked shins".  The front of the young horse's cannon bone becomes swollen due to microscopic painful stress fractures caused by the onset of heavy work. This can be prevented by introducing light exercise to yearlings to strengthen their bones and ligaments and only very gradually increasing the training program demands.

The other bone of the horse's front leg that you've probably heard of is the Navicular bone.  You can see it above between the pastern bones and the bone inside the hoof.  Navicular Syndrome is the name used for heel pain in horses and though the Navicular bone itself may become weakened over time, the muscles and ligaments in this area may also be the source of discomfort for the horse. Vets can help diagnose the nature of the horse's lameness and prescribe appropriate treatment.

Check back for the next installment to learn about ligaments, tendons, & the suspensory apparatus!

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