Picture your dog jumping an obstacle. He launches his body into the air, and then depends on his front limbs to absorb the shock of landing. In order to do all this, all of his joints need to be working right.
Your dog’s joints consists of two bone ends, a fibrous joint capsule, and the space between the bone ends, which is filled with thick joint fluid. Smooth cartilage lines the ends of the bones. Surrounding the joint is an array of supportive soft tissue, tendons, ligaments and muscles. When the bones jostle around from activity, they are cushioned by the joint fluid and supported by the surrounding tissue.
The joint has dual actions that leave it vulnerable to injury. It needs to allow for maximum movement, flexion and extension; but it also needs to remain stacked for limb support during load bearing. These are opposite but vitally important actions. One without the other leaves the dog disabled.
When a joint moves, nerves signal some muscle groups to contract, and others to relax, leading to flexion or extension. The cartilage on the bone endings, bathed in joint fluid, allows the limb to bend smoothly.
The tendons and ligaments surrounding the joint not only allow movement, but protect the joint from harm. Muscle tissue that’s too weak can’t keep the joint from sliding out of place, leaving it unprotected against jarring movements. In contrast, particularly strong muscles around the joint can be inflexible and lead to strains. Muscle strains will heal, but damage to the cartilaginous bone ends of the joint can be much more serious.
Cartilage: joint protector
Cartilage allows the joint to glide unimpeded. It also contains a high concentration of nerve fibers to protect the bones, and is so sensitive that even small changes in the joint fluid’s viscosity can cause an achy feeling from the slight friction. Cartilage signals the brain via pain whenever there is an issue in the joint. The pain allows the body to respond before damage occurs or worsens.
If the soft tissue surrounding a joint is not balanced, the joint will not be properly supported. If the joint fluid is thin, it won’t be able to absorb mechanical stress, and the bone endings will get dangerously close together. Cartilage plays a role by absorbing some of the mechanical stress – or causing pain to warn the body that the bone ends are coming into contact. If the dog does not respond to the pain, the bone ends can collide and cause damage to the cartilage, or even result in a fracture.
Cartilage is not fed by blood vessels, which means that when it’s damaged, it will never return to its original state. Once traumatic injury has begun in the cartilaginous surface of a joint, it becomes more difficult to prevent or reduce the effects of further trauma.
When cartilage is damaged, the body replaces it with an inferior fibrocartilage that is prone to chipping and breaking. If the joint capsule becomes inflamed, hydrolyzing enzymes that break down the complex proteins in joint fluids are released. This weakens the joint’s ability to protect itself from further damage. A weakened form of cartilage and lack of viscous joint fluid means injured joints face further jarring action and more damage.
Whenever a joint is damaged, it becomes inflamed. Arthritis, bursitis, tendonitis – all the “itises” refer to inflammation as a result of tissue damage. The combination of joint damage and increased pressure from the inflammation places stress on the soft tissues in and around the joint.
Exercise and nutrients
People often ask me if they should continue exercising a dog with hip dysplasia or arthritis. My answer is that activity in moderation helps tone the muscles around the joint, and keep the joint moving. Swimming and underwater treadmills allow a dog to build muscular strength and support his joint health without pressure or concussion. However, strenuous activity such as jumping and fast directional changes should be minimized.
Joint fluid consists primarily of unique sugars. They combine amino acids to create compounds with some exceptionally concussion-absorbent properties. The drawback of such specialized fluids is that they are difficult to find outside joints. Easily accessible joint supplements I recommend include glucosamine, chondroitin and hyaluronic acid. They can help replace lost viscosity in joint fluid, and be used as a building block to repair joint cartilage, and lubricate joints, respectively.
Your dog’s joints are delicate, so treat them right, feed and maintain them, and keep the muscles around them toned and limber.