Joint issues are one of the major issues that all horse owners face. This article aims to provide a general understanding of basic concepts around joint health. Importantly, the take home message from this article is that, when it comes to joint structure, joint function and joint health, there is little difference between us, as riders, and our horses.
We have all experienced joint-related pain in one form or another – this may have been due to a trauma or something that gradually develops over time. Like us, our horses also experience joint-related pain. However, unlike us, they can’t tell us exactly what is going on, so we need to gain a greater understanding about how joints work, what we can do to maintain them and what we should consider when things go wrong.
What are articular joints?
Joints are a relatively simple structures composed of articular surfaces (moving surfaces) that come together within a capsule, called a joint capsule.
It should be noted there are no blood vessels, lymphatic channels, or nerves that enter or pass through joints.
The two articular surfaces of the bone are covered in a very tough and sheer resistant tissue, called hyaline articular cartilage (HAC).
In order for joints to move, the two opposing surfaces need to glide over each other with minimal effort and lubrication is central to this process. The cartilage covering the bone has a thin layer of hyper-hydrated proteinaceous material adhering to the surface of the cartilage.
This proteinaceous material is made of proteoglycans, which is essentially a combination of proteins and a special type of sugar molecule, called glycosaminoglycan (GAG).
It is the proteoglycan within the proteinaceous layer that provides hydration and lubrication to the cartilage surface. What this means is that, when the joint is ‘functionally normal’, cartilage does not touch cartilage. Instead, the layer of hyper-hydrated proteinaceous molecules interfaces with similar material on the opposing surface.
Under load-bearing conditions, this boundary ‘weeps’ water into the synovial fluid, thereby dissipating the pressure. When load-bearing conditions cease, the water is re-absorbed and the proteoglycans are again hyper-hydrated.
The other aspect to lubrication and protection of the joint is synovial fluid. The synovial membrane is the inner layer of the joint capsule. This membrane secretes a thick fluid, called synovia, that serves to lubricate moving parts and nourish the cartilage surface.
Healthy synovial fluid is essentially a thick viscous substance made up of plasma filtrate (blood), along with synovia, and is the major source of nutrients for the cartilage tissue and its repair.
Joints’ wear and tear: Osteoarthritis (OA) & degenerative joint disease (DJD):
Normal and expected wear and tear, repetitive concussion and acute trauma can result in chronic progressive degeneration of the joint cartilage, narrowing of the joint space, bony changes, such as bone spurs, along with thickening of the synovial membrane.
The process of deterioration, as a result of injury, is complex but, essentially, the deteriorating cartilage releases molecules into the synovial fluid that cause inflammation of the synovial membrane. The inflammation then triggers the synovial membrane to release enzymes that further contribute to the deterioration of the cartilage.
Joint repair and maintenance requirements
The joint requires particular substrates to meet normal daily repair and maintenance requirements.
The key building block is glucosamine, which is a GAG precursor and a substrate for the biochemical pathway responsible for the production of macromolecules involved in joint articulation, including chondroitin sulfate (CS) and hyaluronic acid (HA).
The rate-limiting step in the synthesis of these macromolecules is the level of glucosamine sulphate substrate available for incorporation into the biochemical pathway. It has been suggested that increasing the quantity of glucosamine substrate pushes the biochemical pathway forward and, in effect, increases the synthesis of GAG’s and potentially repair damaged HAC.
What to do when things go wrong…
The action you take will depend on the circumstances around what ‘clincally’ you are seeing.
Your first port of call for you or your horse should be professional medical advice, more so in the setting of an acute trauma. It’s important to understand that, when there is trauma that involves laceration or puncture of the joint capsules, acute management will be the most important factor in avoiding infection and, more specifically, joint sepsis, thereby ensuring a good prognosis for you or your horse.
Long-term, holistic management of osteoarthritis
The following are some areas for consideration when we take a holistic approach in the management of joint health:
Added weight means added pressure and, over time, this will negatively affect the ability of the joint to meet the requirements of normal maintenance and repair;
Correct exercise is essential in ensuring the joint capsule remains mobile and supple, and thereby allowing nutrients to pass across the joint capsule. Don’t forget the importance of warming and cooling down with stretching. Having well-conditioned muscle enables correct joint articulation and ensures the joints are not inappropriately loading. When its comes to muscle quality, we need to consider it takes a minimum of three months to grow muscle that is both strong and supple, and this is dependent on the quality of the work, genetics, gender, age and any underlying injuries;
Never underestimate the importance of correct and balanced trimming/shoeing. Keeping things simple is always best, where appropriate, though sometimes there are no simple solutions. The environment is one of the most significant factors in terms of hoof quality, so ensure bedding is always clean and dry with urine removed. Notably, horses standing in heavily muddied paddocks/yards is problematic for hoof wall integrity. Treat thrush aggressively and remember there is no value in feeding oral supplements if the environmental factors are not explored/addressed;
This is an area we don’t often consider. Proprioceptors are sensory receptors in ligaments, tendons, muscles and joint capsules. These receptors provide feedback to the brain and the spinal cord with respect to where our limbs are in 3D space, and are part of a mechanism by which adjustment to posture and/or movement are made to help protect the body from injury. For example, a badly placed or twisted foot. Exercising on varied terrain and surfaces helps to keep proprioception well tuned, therefore benefiting both you and your horse;
When horses are stabled, they are not walking and, therefore, joints do not move in and out of loading and unloading positions. Why is this important? Loading and unloading of joints creates changes in pressure within the joint capsule and facilitates the entry of nutrients across the synovial membrane. When horses are stabled for long periods, they are more often in loading position (standing still), which could be considered sub-optimal in ensuring maximal nutrients entering the joint. For a period of time, this is acceptable. However, for horses that are stabled more than eight hours per day for many months – and possibly all months of the year – this could impact the overall joint health of the horse and, more so, if there is an underlying joint issue/pathology. Spelling horses should be an important part of the life of a stabled horse;
The market is flooded with products that are considered joint health products. The standard therapies include glucosamine sulphate, combined with chondroitin sulphate, along with polysulphated pentosan injections (e.g. Cartrophen, Penstosan).
Anti-inflammatories are part of acute management, as well as the management of arthritic flares. Important considerations are that anti-inflammatories only treat inflammation, and do not provide active substrate that can be utilised by the joint for the benefit of maintenance and repair. That’s where oral supplements that contain the correct substrates come into play.
Glucosamine sulphate is a key building block used for the production of cartilage and it is the only form of glucosamine found naturally in healthy joints, rather than the most commonly used glucosamine hydrochloride (HCL). Studies suggest that glucosamine sulphate is a key component of any oral joint product when used in combination with chondroitin-4-sulphate.
Chondroitin-4-sulphate is the major form of chondroitin found in young healthy joints. It is one of the key components that gives cartilage its ability to absorb impact and resist wear. Oral joint supplements should contain chondroitin-4-sulphate due to its low molecular weight (small particle size) which is essential for efficient absorption, as opposed to the commonly used chondroitin-6-sulphate that is shark or marine-derived. Research studies suggest that chondroitin-4- sulphate plays a role in preventing destructive enzymes associated with cartilage breakdown as well as having a general anti-inflammatory action.
The oral supplements discussed here should form the basis of any program for the prevention and management of osteoarthritis in horses. There are other joint health products available, but these should be used as adjuncts to those discussed here, and not as replacements.
For an article about the stages of joint disease, click here.
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