There are 205 bones in the horse’s skeleton. Twenty of these bones are in each foreleg and 20 in each hind limb, for a grand total of 80 bones in the four equine legs. The leg bones do not function independently. Each is connected or aligned with one or more other bones, allowing the horse to lift, bend, and flex its legs. This ability allows the horse to travel across the ground, absorbing concussion as it does so. The spot where one or more bones join is the joint. This installment of the anatomy and physiology series focuses on these critical areas of movement.

Types of Joints

There are three types or classifications of equine joints. They are:

Synovial joints–These are the movable joints and the ones most apt to sustain injury or be afflicted with disease. An example of a synovial joint is the carpus (knee), which actually contains three joints and multiple bones. In a manner of speaking, the synovial joints are the horse’s ball bearings. A synovial joint consists of two bone ends that are both covered by articular cartilage. The cartilage within the joint is smooth and resilient, allowing for frictionless movement. Each joint capsule also contains an inner lining called the synovial membrane, which secretes synovial fluid to lubricate the joints.

Cartilaginous joints–These joints are slightly movable or immovable, depending on the bones involved. Cartilaginous joints are united by fibrocartilage (composed of collagen fibers), hyaline cartilage (translucent bluish white), or both. An example is the connective tissue between vertebrae.

Fibrous joints–These are immovable joints where