We continue our series on equine health with Tina Thorowgood from Vetpro NZ. Today Tina is talking about arthritis, or inflammation in the joint. This inflammation can be of any cause, infection, acute trauma etc. Of more concern however is Degenerative Joint Disease. This is a disorder common in animals and humans alike and usually referred to as DJD.
DJD is generally regarded as a non-inflammatory condition of articular cartilage and is often called osteoarthritis. There are two classifications :
Primary DJD occurs where there is no known trauma or disease but is typical of the joint changes in the older animal.
Secondary DJD occurs where there is some direct trauma or infection of the joint. It can also result from some systemic diseases.
Articular disease comes in two categories also: inflammatory and non-inflammatory and DJD is in the latter, however there may be an intermittent inflammatory phase.
Secondary DJD, and its inevitable progression to damage and painful inefficient joints, can occur at any age and several factors may initiate the start of the disorder. Tina says that once the process starts it cannot be reversed or cured. DJD is the number one reason for premature horse retirement. However, she says that the process can be slowed and relief can be provided that may result in a horse maintaining an active life.
Joints are lined by specialized tissue, called hyaline cartilage that is vital to smooth joint function. This cartilage can become frayed and damaged due to the mechanical wear. The normally smooth glistening cartilage is eroded and becomes thin, ultimately exposing bone and causing pain. With more chronic cases, the soft tissue supporting structures can become thickened which results in a decreased range of motion of the joint.
Tina explains that DJD is not a condition of articular cartilage alone. The synovial membrane which lines the joint cavity, is also affected. If left unattended joints will become swollen and sore and, eventually, new bone is created to strengthen the surface (a process called sclerosis) and extend its margins (bone spurs and osteophytes). In its final stages, if left unchecked, arthritis causes the fusing of equine joints.
Tina stresses that the key to treatment is acting early so that progress of the disorder can be slowed so the horse is pain free and still useful. While it cannot be reversed it can be stopped and symptoms alleviated.
So what causes DJD?
Tina says that the number one cause is trauma, either from a direct one-off blow or repetitive concussive forces. The most common cause is the latter and various factors are involved in the intensity of the forces.
Right at the start a horse should be analysed for conformation defects. If a career is planned for racing, jumping, dressage etc., then an experienced veterinarian should assess whether the conformation is strong and correct enough for the horse to pursue the chosen career to the highest levels.
Overtaxing an unsuitably built horse is likely to produce DJD and maybe a decision not to pursue a particular path may mean that given an easier sport, DJD can be delayed or even prevented.
Tina also says that good intelligent shoeing can assist, but a farrier should not try to correct a deviation of the leg as that will only cause stress on joints which otherwise would not be affected. Good support for your horse's actual structure may alleviate the pressures on the joints. Balanced, level feet with correct angles are vital to assist prevention and incorrect shoeing can often be triggering factor for DJD.
Tina also says that an excessive workload or overly strenuous training can be a causal factor, but the key thing is the surface that the horse is worked on. Trauma from concussion is the most common cause of early onset DJD. She believes that the old-fashioned idea of trotting eventing horses out on the roads to” harden them up”, shows a lack of understanding of these factors and can shorten your horse's competitive life.
What's the best surface to help prevent DJD?
To achieve a workable all weather arena or track that is level and firm throughout the year often means using hard sand or cinders. However, horse owners must also think about cushioning the strike of the leg on the surface. Tina has observed that many surfaces are built as though they were a road, with just a shallow sand surface placed on top. She says that consideration must be given to cushioning that surface if the horse is not to start the negative processes towards DJD.
Overseas surfaces are often deeper and softer, with sand added to rubber, the use of soft chips, or a mix of sand and rubber/plastic. Another option is the use of European fibre sand. Indoor surfaces are often peat.
Your horse's hoof moves forwards and downwards and rapidly decelerates when brought in contact with the ground. It’s this deceleration and strike that causes the concussive effect which can be damaging to joints and bones. The term "impact resistance" describes the way that the footing absorbs that concussive effect, so hard surfaces have high impact resistance.
Tina explains further that shear resistance describes the ease with which the footing is displaced by a shearing (rotational) force. When the leg is pushing against the ground to generate propulsion, the toe tends to rotate into the surface. The shear resistance of the footing should be low enough to allow the toe to dig in as the hoof pushes against it, reducing tension in the distal check ligament and reducing pressure on the deep digital flexor tendon on the navicular region.
This shear resistance can, however, be too low. For example, in deep soft dry sand (as above the tideline at the beach), the ground does not offer sufficient resistance to the hoof pushing against it. Instead, the surface gives way during push off and the muscles have to work harder to generate propulsion. As a consequence of having to work harder, the muscles can become fatigued more quickly and this predisposes the horse's ligaments and tendons to injuries.
Surfaces that are deep and soft will have low impact resistances but very deep heavy soft sand may be detrimental to ligaments and tendons as they will fatigue quicker with the effort of moving the legs through such a surface.
The negative effect of deep sand can be reduced by adding water which will improve the shear resistance as the foot moves through the sand. So riding along the edge of the waterline on a beach is preferable to riding on the deeper dry sand, while still providing a softer surface than hard dry sand.
Tina says that the answer lies somewhere in the middle. Low impact resistance provided by using wood, fibre, rubber and other synthetics etc. Hard and/or dry sand is the worst option and most likely to initiate the process of DJD.
The depth of the hoof print is a good indicator of the impact resistance, the deeper the hoof print, the lower the impact resistance and the concussive effect transmitted to joints and bones.
Left: A hard surface with high impact resistance does not allow the toe to dig in during push off.
Centre: A surface with moderate impact and shear resistance allows the toe to dig but then offers resistance as the hoof pushes off.
Right: A soft surface with low impact but low shear resistance and gives way and does not offer sufficient resistance as the hoof pushes off.
Scientific studies have shown actual measurements of impact force is much greater with sand. This can be dampened (reduced in force), by the addition of water or wood or fibre.
Three levels of force were classified, the greatest being dense hard (asphalt), surfaces with friction damping (sand), the least being surfaces with structural damping (wood fibres).
Whilst the cheapest option maybe hard shallow sand, it may be the most expensive if it shortens the active life of the joint and bones of the horse!
Tina says that when veterinarians check a horse for lameness, they run it on a hard surface. This is because the horse is much more likely to show lameness on such a surface ….. Go figure!
Direct trauma to the joint can often develop into DJD, but any injury to a joint, strains, sprains, direct impact should be investigated and monitored so that the possibility of DJD is noted before it becomes chronic.
What are the signs of DJD?
At first your horse may not show actual lameness, but if DJD develops this will come eventually.
Initially the usual pain signs of discomfort, ears back, grumpy reaction to being pushed to move, restless tail when moving, personality change, then shortened steps, feeling to the rider of a jarring through the horse. DJD then progresses into stronger reactions to pain, refusing to go and more negative responses even when handled.
Tina says that, sadly, some of the early signs are sometimes missed with inexperienced owners/trainers and the horse may be forced often with the whip.
Early on there may be a mild lameness which seems to come and go. It improves with a turn out to pasture but returns and increases the harder the horse is worked.
If the joint has a capsule that is distensible then some swelling and maybe heat is seen and felt. But if the joint is one that is contained by strong ligaments and or tendons, then swelling may not be evident.
Tina stresses that early attention to the signs is very important as, while the process is not reversible, it can be ameliorated and held at a minor level.
To obtain a diagnosis a veterinarian may carry out an intra-articular block, using local anaesthetic. After the area of the pain is located, X-rays will be taken to help establish the cause. Also, a sample of the fluid from the joint (synovial) can be tested to indicate the presence of arthritis. This can also indicate the extent of the degeneration by the count of the cartilage and bone cells.
Possible bone fractures are also detectable. The use of x-rays alone can create misleading diagnosis, indeed in the early part of the disease very little sign of DJD may show on x-ray. Some changes may show and could mis-lead the diagnosis, so x-rays are used after other signs are confirmed, merely to assess the extent of the disease, or to show fractures or developmental abnormalities which may be the true cause of the pain. Bone spurs are not an indication as they can exist in pain free joints.
Arthroscopy is an option, where an optical tube is inserted into the joint to give the veterinarian a view of the joint and its issues. Changes can be seen as an area of dullness on the cartilage, colour change from glistening white to a mottled grey or even yellow.
However, this is an invasive procedure into the joint and has all the risks of that invasion. It is usually carried out by a specialist (in which a slender optical instrument is inserted into the joint cavity) and gives the most definitive diagnosis of arthritis, as your veterinarian can actually see the extent of the damage. Most veterinarians, however, do not routinely use arthroscopy as a diagnostic because it is an invasive procedure requiring anesthesia.
What Can be Done?
As Tina has explained, DJD is not curable. Its a progressive disorder, so the very best remedy is to prevent it.
As always, experience is needed to successfully care for and work with a horse. If you don’t have that experience to truly provide a balanced healthy diet, a correct work or exercise regime, understand conformation and shoeing and provide the specific care after trauma or injury, then you should seek qualified and expert assistance. Lack of education and knowledge creates many of the unnecessary chronic conditions in a horse.
The best way to prevent the onset of DJD is to start good balanced nutrition right from the start. This will maximise quality bone and joint development. Before breaking in, a horse should be assessed for his conformation and be trained in a way that is appropriate to that confirmation.
Going forward, your horse must be well shod (balanced and level and true to his angles) by an experienced person, in a way that reduces stress and concussive forces to the joints.
The work requirement should be planned to not be overly excessive in the younger years and, most particularly, great consideration must be given to the surface that the horse is required to work on.
If DJD does develop, recognising the signals from the horse early can make a big difference in stopping further progression.
It has now been shown with scientific studies that using a nutriceutical that has the correct active ingredients in the correct quantities has a recognised beneficial effect on joints that are showing signs of DJD. These types of products help to maintain the quality of the cartilage and retain its elasticity and shock absorbing qualities.
Ideally a nutriceutical should be used before any chronic DJD develops, especially with horses that may be vulnerable for any of the reasons given above.
Prophylactic use can assist where a horse is required to work at a young age, as with racing both harness and thoroughbred. However, the nutriceutical must have certain active ingredients as proven by scientific test to be effective and they must be at the levels also scientifically shown to be effective.
The use of injections directly into the joint, (only carried out by a veterinarian) in combination with a suitable nutriceutical, like Flex Equine Plus, has also been scientifically proven to reduce the negative reactions to DJD.
This combination has been proven to reduce the number of injections required, and therefore the cost. Likewise intra-muscular injections of products like Pentosan, in combination with the same high standard nutriceutical, can have similar benefits for horses not quite at such a level of the disease.
Varied lengths of paddock rest can prolong the active use of the horse but, as discussed, a chronic condition is not reversible and becomes a maintenance regime to reduce the level of discomfort and achieve some extension of the horse’s competitive years.
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Reference’s for sources for this article:
M Cruz DVM, MVM, Msc, DrMedVet
A.J Lipowitz, C.D. Newton
E.Barrey, B. Landjerit, R Wolter Ecole Nationale Veterinaire d’Alfori France, Laboratoire de Biomecanique de L’ENSAM
R.Lamberski, R A Lobos, Dr. D J Burba
Dr. H M Clayton BVMS, PhD, Diplomate Michigan State University.