Osteoarthritis is a chronic, degenerative disease, which impacts one or more joints of the body. Dogs and horses can both suffer from the disease; equine osteoarthritis has been reported as the cause of up to 60% of cases of equine lameness (USDA, 2000). It is most commonly found in synovial joints, such as the knee (carpus), fetlock or hock in a horse or elbow, wrist or hip in a dog. Osteoarthritis in a joint results in a reduced range of movement and can cause significant pain.
The Synovial Joint
To understand how osteoarthritis impacts the joint, let's first look at the synovial joint in more detail.
Synovial joints are formed when two or more bones meet. As you can see in the diagram above, the end of each bone is covered in a layer of hyaline or articular cartilage. This helps to reduce friction or bone trauma during movement. The joint is surrounded by the joint capsule, which encases the synovial membrane on the inner wall. This is a vascular tissue (meaning it has good blood flow) which creates synovial fluid. Synovial fluid nourishes the cartilage at the end of the bones and provides lubrication for the joint to promote smooth and comfortable movement. These types of joints allow for a greater amount of movement and can be described as ball and socket, hinge or gliding joints. However, too much movement, such as over extension or over flexion, would be bad for the joint. Therefore, the shape of the joint and the connective tissue which surround it prevent this from happening.
Osteoarthritis is initiated by inflammation, which can begin in any of the synovial tissues of the joint.
What causes inflammation within a synovial joint?
There are a number of causes or conditions which can instigate the inflammatory cascade, which then leads to the to the development of osteoarthritis. Here are some examples:
Trauma – this might be the site of a bone fracture or injury, which will have been subject to inflammation during the healing process. This can cause damage to cartilage.
Age related degeneration- like many of our systems and tissues, joints can begin to degenerate as we age and it is the same for our animals.
Osteochondrosis (OCD)- this is a developmental disease in which the development of the bone is disturbed.
Abnormal load on normal cartilage – this is problematic because the normal cartilage is unable to withstand an abnormal load for a significant period of time without being negatively affected. This can happen when injury impacts another part of the body and to compensate, abnormal load is applied elsewhere.
Normal load on abnormal cartilage- although in this occurrence the load being applied to the joint is normal, the abnormality of the cartilage means that it is unable to support the load appropriately.
Once the inflammation process is initiated in one of the synovial tissues, something called inflammatory mediator production begins. This means that inflammatory mediators (which are the molecules within our bodies which are responsible for causing inflammation) are released. These inflammatory mediators act on other tissues within the synovial joint. In response, these tissues then also begin to produce more inflammatory mediators, resulting in a ‘domino effect.’ This is not good for the joint as inflammatory mediators cause the cartilage within the joint to begin to break down, resulting in a softer cartilage that is more easily damaged under load. The quality of the synovial fluid also begins to decline; it becomes thin and the joint space is reduced, while the once flexible and mobile synovial membrane becomes fibrosed and rigid. Eventually, the cartilage is so damaged that subchondral bone is exposed. As the joint space has been reduced, the two ends of bone within the joint can now touch and sclerosis (hardening and thickening of the bone) begins to occur. This then contributes to further inflammation and a chronic progressive cycle of osteoarthritis.
Treatment of Osteoarthritis
Unfortunately, there is currently no cure for osteoarthritis. If cases are detected in the early stages, treatment aims to prevent further progression of the disease by reducing the inflammation within the joint. However, when diagnosis is made in the later stages and the osteoarthritis is already causing pain, treatment aims to reduce pain and then maintain the current state of the already damaged cartilage and prevent further degeneration. Your veterinary surgeon can administer anti-inflammatory drugs to manage osteoarthritis. These are injected directly into the joint to quickly reduce the pain and inhibit inflammation. Although these injections are normally successful, there is some concern that over use can cause further degradation.
How can physiotherapy help to manage osteoarthritis?
There are a number ways in which physiotherapy can help you to manage osteoarthritis in your horse or dog.
Laser therapy can be applied to the joint. Laser therapy helps to regulate nerve sensation and reduces inflammation, which reduces pain. Reducing inflammation also helps to reduce the risk of further degeneration.
Massage therapy can be applied to muscles which surround and act on the joint. When a joint is effected by osteoarthritis and becomes painful, animals can begin to avoid using it properly. This impacts the muscles which either flex or extend the joint as they stop being used to their full capacity. This not only results in loss of muscle mass and strength, it also results in a reduction in circulation. This is not good for muscle health as nutrients will not be brought to the muscle as effectively, and waste products will not be removed. Massage can help to improve muscle health by improving circulation to the muscle and improving tissue extensibility. This not only helps to improve the health of the muscle, it will also help to improve the joint range of motion (ROM) once pain management has taken place, as the muscle will be in a better position to work effectively on the joint. Massage can also be an effective tool in addressing compensations where other parts of the body have been working harder to compensate for the reduced ROM or load bearing capacity of the injured joint/limb.
Passive and active ROM- when a joint is inflamed and painful, your horse or dog will begin to use it less and less. This begins a vicious cycle. The muscles and soft tissue structures associated with the joint will loose strength, extensibility and ROM. This will lead to a further reduction of ROM in the joint itself as the muscles and soft tissues which act upon it reduce their ability to fully function. However, once pain has been addressed, a veterinary physiotherapist is able to use either passive or active ROM exercises to help improve or restore your animal’s joint ROM in a safe and empathetic way. This is important to maintain the joint health as it stimulates the production of synovial fluid, which we have already seen is needed to nourish the cartilage. It also helps to further stimulate circulation in the muscles which will have been massaged and supports improvement of tissue extensibility and correct fibre alignment- something which may have become compromised if muscles have not been used.
Exercise therapy- After working directly with your horse or dog, your veterinary physiotherapist will provide you with some exercises to support your animal's long term goals. These will have been specifically selected to continue to actively take joints through their ROM, to promote long term joint health and osteoarthritis management. Active ROM exercises are ones which the animal carries out themselves, meaning there is much less risk of causing pain or taking the movement too far. You will also be given exercises to build muscle strength. The focus will be on building strength in muscles connected to the injured joint, to maintain strength and support. There will also be focus on strengthening the musculoskeletal system as a whole so that it is capable of providing additional support to compensate for the weaker area. Core strength is extremely important for this.
Although all of the above can provide effective long term support for your horse or dog and help them to comfortably maintain an active lifestyle, there may become times when they again require a little more veterinary support or treatment. This is often nothing to worry about and usually just means the joint requires re-medicating. Your veterinary physiotherapist will be able to identify the signs that this is required and therefore highlights the importance of having regular appointments for your animals with osteoarthritis; your vet physio will be able to get to know your animal, what is ‘normal’ for them and therefore quickly identify when they need a bit more support.
USDA, L., & Lameness, V. S. (2000). Laminitis in US Horses. USDA: APHIS: VS, CEAH, National Animal Health Monitoring System N, 348. https://www.aphis.usda.gov/animal_health/nahms/equine/downloads/equine98/Equine98_dr_Lameness.pdf
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