Equine Joint Structure
By Linda Kennard, NAF
Joints allow the limbs to flex and bend. The horse's joints are designed to effectively absorb shock, permit frictionless movement and effectively bear the weight of the body.
There are basically 3 different types of joints, fibrous, cartilaginous and synovial.
Fibrous joints are the least likely to be affected by wear and tear because they are more or less immobile. These joints are found in the skull and between the shafts of some long bones.
Cartilaginous joints do not have a natural tendency for degeneration as they have limited movement. These are the joints of the pelvis and vertebrae as well as the growth plates. Growth plates extend the bone length during the horses growing years.
Synovial joints consist of two bone ends covered by articular cartilage. These are the joints that are most likely to degenerate in quality and more prone to injury because they are the most active joints in the horse's body.
The articular cartilage within the joint is smooth and resilient and when properly lubricated enables frictionless movement of the joint. The joint stability is maintained by a fibrous joint capsule, which attaches to both bones and the collateral ligaments at the sides of most joints. These are the key components of the fetlock, knee, elbow, hock and stifle.
Other ligaments help to stabilise selected joints, such as the cruciate ligaments in the stifle joint.
In addition there are other ligaments (outside the joint cavity) that also support the integrity of the joints. An example of these would be the distal sesamoidean ligaments and the suspensory ligaments, which along with the sesamoid bones, make up the suspensory apparatus and hold the fetlock in the correct position.
The joint capsule itself is made up of the fibrous capsul and an inner lining layer called the synovial membrane. The synovial membrane controls the composition of the synovial fluid.
Synovial fluid is vital for the nutrition of the articular cartilage and has an important role in the lubrication of the synovial membrane and the joint capsule.
A prime enemy of joint health is friction. Therefore to protect against friction lubrication is needed.
Cartilage has no nerve supply; therefore damage to the cartilage does not itself cause pain. It has no blood supply and is dependant on the synovial fluid for its nutrition. If movement of the synovial fluid in and out of the articular cartilage is impaired then the cartilage receives inadequate nutrition resulting in cell death and a decrease in resistance to stress.
There are various degenerative disorders that affect the nature of the synovial fluid caused by a breakdown in the integrity of the synovial membrane. The most common seen by the horse owner being arthritis (inflammation of the joint) which is excessive fluid production. This is caused by an unhealthy synovial membrane which becomes prone to producing synovial fluid that has a lower viscosity (i.e. more watery).
As the health and integrity of the joint and its components deteriorate unlevelness can be seen in the horse, although it is worth noting that minor damage to the articular cartilage alone does not always cause discomfort and therefore can often go unnoticed.
Recommended NAF products: Five Star Superflex Liquid, Five Star Superflex Powder.
For further details visit you local NAF stockist or
call the NAF Freephone Advice Line: 0800 373 106.
Alternatively go to www.naf-uk.com
