Equine Reciprocating Systems: Extreme Skeletal Specializations

In this sixth installment, Dr. Deb Bennett discusses the impact of the equine joint shape on the horse’s forelimb

Pictured Above: Comparison of equine and human ribcage in dorsal view. The drawing makes the length from first thoracic to the cranial surfaces of the sacrum equal; this causes other proportional differences to stand out. All images: Deb Bennett

Farrier Takeaways

  • The only joint of the equine forelimb that can rotate and whose motions are not confined to a narrow fore-aft plane is the shoulder joint.
  • As the humerus goes, so go all parts of the limb below it. Inward or outward rotation at the shoulder joint is the ultimate determinant of toed-in or toed-out stance.
  • Because the scapula glides over the curved surface of the ribcage, the orientation of the plane in which the equine forelimb folds and unfolds is not parallel to the midline plane of the body. The two planes orient, for the most part, independently.

Most, if not all, farriers are already familiar with the chain of bones that forms the equine forelimb: scapula, humerus, radius-ulna, carpal bones, cannon bones and splints, pastern bones and coffin bone. Added to this list are the three pseudo-bones called sesamoids, which lie behind the ankle and coffin joints. Joints form where bones meet. Specializations of equine joint shape have a big impact on the way the horse’s forelimb functions. Because joint shape dictates movement capability, the architecture of the horse’s joints is the ultimate determinant and guide for forelimb reciprocation.

The basic function of the skeleton is to support the weight of the body against the downward pull of…

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Dr deb bennett

Deb Bennett

Dr. Deb Bennett has studied classification, evolution, anatomy and biomechanics of the horse. She worked at the Smithsonian Institution, until founding the Equine Studies Institute. She is an author who has published four books on horse-related topics, in addition to articles in most major equine magazines in North America.

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