Osteoarthritis (OA) is considered the most important musculoskeletal disorder in both humans and horses. From a clinical perspective it is associated with lameness and dysfunction of the affected joint, and approximately 60% of all equine lameness is due to OA. Significant economic loss occurs as a result and coupled with welfare concerns, motivates ongoing research into innovative treatments. The rapid resolution
of lameness by a reduction in pain is paramount, but treatments ideally, should also serve to arrest or slow the progression of the disease.

The use of an intra-articular 2.5% cross-linked polyacrylamide (2.5% PAAG- Arthramid® Vet) to treat OA is novel. Following injection into the joint 2.5% PAAG is adsorbed into the synovial membrane through a combination of vessel in-growth and molecular water exchange and persists long term in the joint. This significantly improves joint lameness caused by both early (acute) and late (chronic) stages of OA, with clinical trials showing up to 82.5% of cases becoming lame free for up to 24 months. Significantly longer than current treatments.

Current Treatments for Osteoarthritis (OA)

Osteoarthritis (OA) has traditionally been treated symptomatically in the horse. If rest alone is selected as a treatment option then this is often the result of financial constraints or owner expectations. However, periods of rest are often not possible or indeed desirable for performance horses. Current conventional therapies therefore have included non-steroidal anti-inflammatory drugs (NSAIDs), polysulphated glycosaminoglycans (PSGAGs), corticosteroids, glucosamine, epiitalis, hyaluronic acid and a combination of the above, along with biotechnological substances such as gene therapy, recombinant or autologous growth factors (platelet-rich plasma and interleukin-1 receptor antagonist) and stem cells (allogeneic and autologous chondrocyte transplantation).
The challenge is to develop therapeutic options that both reduce pain and are disease modifying. This would reduce the progression of the deleterious effects OA has on the articular cartilage and surrounding joint structures.

Intra-articular (IA) corticosteroid administration is one of the most commonly used treatments. Concerns for its ongoing use include steroid-induced deterioration of articular tissues, known as “steroid arthropathy.” The overuse of a treated joint may also result in accelerated cartilage degeneration. These primary concerns are compounded by additional reports of the adverse effects corticosteroids have on cartilage metabolism. Horse Racing Authorities globally have acknowledged these types of studies and through racing and welfare committees now recommend a minimum 14-day up to 28-day stand-down period as a result. IA corticosteroids are commonly combined with hyaluronic acid (HA). There is the perception that the HA might be protective against any deleterious effects of corticosteroids. Studies, however, reveal little or no improvement of OA scores with this treatment and show little protective effect of HA against induced cartilage breakdown.

The ideal therapeutic agent for a horse suffering from OA is therefore an agent that alleviates the symptoms of lameness while also providing a positive effect on the articular components resulting in stabilisation or even repair of the disease processes occurring in the affected joint. The era of OA management is shifting towards new therapeutic concepts.

What causes Osteoarthritis?

There are three possible disease pathways for OA.
The most commonly accepted theory is that cartilage gets damaged due to different mechanical forces, which generates injury to the cartilage cells and matrix, which will start a cascade of a release of enzymes resulting in cartilage breakdown.
Cartilage is relatively susceptible to repetitive trauma compared to its ability to resist shear forces. Therefore, repeated trauma is assumed to be one of the most common factors of OA in horses.
A second pathway describes the cartilage as being principally defective, with abnormal biomechanical properties that will fail under normal loading. This is most applicable to young horses with underlying developmental joint issues (so called development orthopaedic disease or DOD). Osteochondrosis (OCD) is the most common form of this type of disorder and can result in poor quality cartilage and even fragments that pre-dispose the joint to developing OA.
The third pathway involves physical changes in the subchondral bone (bone underneath the cartilage). The thin articular cartilage cannot work as an effective shock absorber, therefore the subchondral bone protects the cartilage from damage by providing a flexible surface to absorb forces placed on the joint. This cause originates most often from overuse and conformational problems (offset knees, angular limb deformities, etc) predisposing the horse to inappropriate biomechanical forces on the articular cartilage.

In athletic and young horses, synovitis and capsulitis are changes that occur early on and are assumed to be associated with repetitive trauma. This cause originates most often from overuse and conformational problems predisposing the horse to inappropriate biomechanical forces on the articular (joint) cartilage.

What are the signs my horse has arthritis?

Arthritis describes inflammation of a joint. The term incorporates synovitis, capsulitis, sprain, intra-articular fracture, meniscal tears (stifles), and OA. Sub-chondral bone injury also plays a role. Although these conditions are a group of overlapping distinct diseases, they all share a similar biologic, morphologic and clinical outcome; being that of lameness. Any lameness in a competition horse should be considered serious. Even low level lameness can have a tremendous effect on welfare, trainability and performance.

In athletic and young horses, synovitis and capsulitis are changes that occur early on in the OA disease process. Inflammatory mediators (cytokines, prostaglandin E2, and matrix metalloproteinases) are released by reactive synovial cells in response to cartilage wear within the joint fluid. Clinically, synovitis is seen as a palpable joint swelling due to either synovial (joint) effusion or thickening of the joint capsule. If this persists, fibrosis and increased friction in the joint capsule will develop, resulting in thickening of the joint capsule and loss of the normal range of joint motion. Therefore rapid resolution of synovitis and capsulitis is critical in the management of OA because synovitis induces cartilage breakdown.

Lameness attributable to pain is the major clinical sign that a horse has OA. It is notably also the principal concern of owners and trainers and the reason why horses present for veterinary care. It is important to appreciate that there is often a weak correlation between the magnitude of pain and the severity of arthritic damage. However, it is the ongoing presence of pain and inflammation that leads to a continuation of the vicious cycle of cartilage damage and degeneration that ultimately leads to a joint becoming degenerative and unresponsive to treatment (end-stage arthritis). This has the affect of ending the animals career, as well as raising welfare concerns for the horse and their owners.

What is Arthramid® Vet?

Arthramid® Vet is a sterile injection of 2.5% cross-linked polyacrylamide (PAAG) material bound with water molecules to create a safe and inert hydrogel that contains no active pharmaceutical compound. Once injected into the joint it acts as a bio-scaffold, being adsorbed and integrated into the joint capsule and forming a thick cushion-like membrane that increases the elasticity and tensile strength of the joint capsule itself. It is this ability to restore the joint to healthy function that treats the synovitis and capsulitis associated with OA and disrupts the cycle of pain characteristic in animals suffering with OA.

Is Arthramid® Vet the right treatment for your horse?

As described previously, horses of any age can develop OA and with a number of underlying causes, so it is important to ensure that an accurate diagnosis is made.  Arthramid® Vet can be used in any synovial joint with signs of OA such as pain, effusion (fluid), reaction to flexion or visible lameness. The treatment of multiple joints is safe and both acute (recent) and chronic (longer-term) cases are suitable. The ideal candidate are those where veterinary assessment has localised the pain to a specific joint and OA has been confirmed by intra-articular analgesia (nerve blocks) and ancillary diagnostics such as radiography, ultrasound, scintigraphy or CT/ MRI.
The clinical syndrome of OA is quite variable, with differences in affected joint patterns, risk factors, rates of progression, and severity of symptoms.
The most commonly treated joints include carpi (knees), fetlocks, hocks, stifles and coffin (DIP) joints, although success in other areas has also been demonstrated. It is best to plan treatment early on in the season as the product takes around 2 to 4 weeks to have its full effect. The veterinarian will determine the dosage for each joint depending on the severity of the disease, size of the joint, and time since onset of the lameness. A response to treatment can be seen for up to 2 years, or even longer in some cases, although repeat treatments can be given at shorter intervals (2 to 12 months) should clinical signs return.

The horse should be rested for 48 hours after treatment and a plan put in place to reduce their workload (no galloping or competing) for 4 to 6 weeks to allow full integration of the gel. It is important for owners to understand this time lag as it contrasts with conventional treatments where a more immediate response is expected. As a result it may also be best to consider treating during periods of reduced exercise demands or earlier in the training programme than would normally be considered. A follow up examination at 4 to 6 weeks is advised to assess the response to treatment.

Where to from here?

Equine veterinarians have a range of options to treat lameness in horses caused by osteoarthritis (OA). They, and horse owners, must use all means at their disposal to ensure horses are exposed to the absolute least amount of discomfort and pain, and potential for injury, while under their care. Intra-articular (IA) corticosteroid administration is one of the most commonly used treatments, employed principally for their immediate and powerful anti-inflammatory effect. However, these, and non-steroidal anti-inflammatory drugs (NSAID’s), treat the symptoms and provide temporary pain relief without addressing the underlying cause of the painful and debilitating condition.

Research firmly shows that 2.5% PAAG is more effective in treating OA than conventional treatments and its adoption by veterinarians and owners will allow a progressive reduction in the use of corticosteroids, such as triamcinolone, and other anti-inflammatories in horse racing and other competitive horse sports. New bio-technologies like Arthramid® Vet now give us the means to improve the safety and well-being of our equine athletes and to reduce the potential for injury – all it takes is knowledge and a change in mindset. There is mounting evidence that these new products (2.5% PAAG) are a game changer in the management of joint pain in osteoarthritis, and we should be very grateful for the research and innovation  that has allowed these products to be available.

Dr Jason Lowe

Equine Veterinarian