Form and Function of Joints

Race Horses

An important relationship exists between your horse’s joint angle, hoof flight pattern and weight bearing. Get any out of whack and you can end up with lameness.

There are three types of joints:

Fibrous Joints

These basically don’t move and are joined by fibrous tissue. They are found in the skull and between the shafts of some long bones.

Cartilaginous Joints

These have a bit more movement, but their range is still limited. Included in these types of joints are the pelvic and spinal joints.

Synovial Joints

These are the most active in the horse’s body and are the ones that will normally have a strong bearing on hoof flight pattern – much like ball bearings. They consist of two bone ends covered by articular cartilage, which is smooth and resilient, and allows for easy movement of the joint when properly lubricated with synovial fluid.

How a Joint Stays Stable

Joint stability is maintained by a fibrous joint capsule, which attaches to both bones, and collateral ligaments. The collateral ligaments are found on either side of most joints. They are important in maintaining stability in joints such as the fetlock, knee, elbow, hock, and stifle.

Other ligaments within the joint, such as the cruciate ligaments, also help with stability. These ligaments provide important support.

How a Joint Moves

Joints need proper alignment if they are to remain healthy. A joint that is not aligned correctly bears inappropriate strain throughout the entire structure.

Not only is proper hoof flight altered by misalignment, but the potential for injury and disease from improper weight bearing is increased.

• Swing Phase – The swing phase, when the horse’s hoof is not in contact with the ground, does not result in great stress on poorly aligned joints. In the swing phase, the limb is first pulled forward, then pulled backward in the final movement prior to ground contact. The force on tendons and ligaments of the joints during the swing phase are very small.

• Ground Contact – The first contact is either heel first, flat-footed, or toe first, depending on gait, speed, farriery, and/or lameness.

• Impact Phase – The impact phase occupies the first 50 milliseconds (one-twentieth of a second) after the hoof touches the ground. During this time, the limb undergoes rapid deceleration that causes a shock wave to travel up the horse’s limb. Important shock absorbers at this point are the joints. During the impact phase, the bones receive their maximum amount of shock, so this is the phase when most bone and joint injuries occur.

• Loading Phase -. During this phase, forces are applied more gradually than during impact, and it is during this phase that ligaments and tendons are maximally loaded. Naturally, this is the phase when most soft tissue injuries occur.

• Breakover – The breakover phase begins when the heels leave the ground and begin to rotate around the toe of the hoof, which is still in contact with the ground.

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