Horse Health Article - Arthritis
Osteoarthritis or degenerative joint disease is one of the most commonly occurring conditions in the modern sport horse, responsible for over 60% of lameness in horses (McIlwraith et al., 2012.) This article addresses how osteoarthritis occurs, the common locations in the horse’s body in which it occurs, and treatment options available to treat it.
What is osteoarthritis?
Osteoarthritis (or “arthritis” for short) is used to describe a condition of the joint whereby the articular cartilage has been degraded. While articular cartilage degeneration is the “end result” of osteoarthritic processes, there is a large sequence of events that leads to this eventual breakdown.
How does arthritis happen?
There are two major pathways in which arthritis occurs in horses:
Normal forces on abnormal cartilage
Abnormal forces on normal cartilage
The second pathway can be considered in horses that have had a traumatic injury to a joint or its supporting structures (e.g. racehorses with a subchondral bone fracture leading to secondary cartilage, or a horse with a ligament tear that destabilises the joint, leading to abnormal loading on the cartilage.)
However, the majority of cases occurring in sport horses are as a result of normal forces acting on abnormal cartilage.
This cartilage degeneration occurs due to a primary inflammation within the joint capsule (synovitis), leading to increased levels of inflammatory mediators and breakdown enzymes (such as IL’s, TNF-a, MMP’s) within the synovial fluid. These chemicals then cause direct damage to the articular cartilage cells (known as chondrocytes), which leads to the structural degradation of the articular cartilage.
Above: Figure 2 from “The horse as a model of naturally occurring osteoarthritis” (McIlwraith et al., 2012.) showing the sequence of events leading to osteoarthritis at the cellular level.
How do we treat arthritis in horses?
Treatment options for arthritis should be applied to address two major factors: the symptoms of the disease, and the disease process itself. There are multiple treatments available on the market, which due to the exciting new developments in modern medicine, means we have more available to treat this condition than ever before.
Systemic anti-inflammatories
The word “systemic” in this case means “affecting the whole horse,” i.e. through a drug that affects inflammatory processes throughout the body, rather than just localised to the joint.
The most common type of anti-inflammatories used in horses are non-steroidal anti-inflammatories (NSAIDs) such as Phenylbutazone and Firocoxib.
Firocoxib (Equioxx (USA) or Prevequine (Aus)) is a COX-selective non-steroidal anti-inflammatory. This means that unlike Phenylbutazone, which targets all COX enzymes throughout the body (increasing the risk of complications such as gastric ulceration), this drug selects the “bad” COX-2 enzymes only (which are increased during inflammatory processes in the body), meaning this drug is safer for long-term use than other non-selective NSAIDs.
Local anti-inflammatories (i.e. intra-articular corticosteroid treatment or “joint injections.”)
“Joint injections” is a term well-known to most horse owners, however the exact “ingredients” used in the recipe injected into the joint is veterinarian-dependent. Most joint injections will involve the injection of corticosteroids into the joint.
Corticosteroids act as a potent anti-inflammatory within the joint, binding to receptors within the joint lining (synovium) to decrease the production of inflammatory mediators within the joint, and also bind directly to COX-2 enzymes within the joint - resulting in potent pain relief.
The frequency of administration required is not clearly defined by the literature, and is often a case-by-case scenario dictated by the individual horse’s response to therapy.
Disease-modifying osteoarthritis drugs (DMOADs) e.g. PSGAG’s/HA/nutraceuticals
In addition to reducing the inflammatory processes associated with arthritis, treatment should also be directed to reducing the development/worsening of the disease.
Within joint cartilage there are groups of molecules called glycosaminoglycans, which bind with hyaluronic acid and collagen to provide “sponginess” of the joint cartilage. Polysulfated Glycosaminoglycans (PSGAG’s) such as Adequan (USA) or Zycan (Aus), are injected into the muscle, diffuse into the circulation and migrate to the joints - where they increase the production of glycosaminoglycans, hyaluronic acid and collagen within the joint cartilage, and reduce the production of inflammatory mediators such as IL-1 to further reduce joint degradation. It is given in the form of intra-muscular injections once every 4 days for a total of 7 injections, repeated every 6-12 months.
Pentosan polysulfate (Pentosan, Arthropen - Aus, Zycosan (USA)) acts by increasing the production of proteoglycans within the cartilage matrix and stimulates hyaluronic acid production by synovial cells. It is given in the form of intra-muscular injections once every 7 days for a total of 4 injections, then repeated as required (usually once every 1-3 months.)
Nutraceuticals such as 4Cyte have been shown to significantly reduce inflammatory mediators produced in experimentally-induced arthritis models and showed markedly reduced radiographic signs of arthritis at day 70 of the study in comparison to placebo horses.
Orthobiologics
New developments in therapeutics for osteoarthritis have yielded the production of an exciting new class of treatment option known as Orthobiologics. These products include therapies such as stem-cell therapy, IRAP and PRP, as well as hydrogels such as Arthramid and Noltrex, which integrate into the joint lining to restore synovial membrane integrity and restore normal function, as well as providing a mechanical increase in joint elasticity to reduce pain from restrictions in range of motion.
PRP, IRAP and stem-cell therapies all involve preparation of samples collected from the horse (either collected through tissue harvesting or via blood collection) and injection into the affected joint/s.
These therapies often preclude intervention with corticosteroids, due to their function to restore integrity of the affected tissue/s within the joint through increased growth factors (or via the stem cells directly, if used), as well as decreasing inflammation within the joint due to the introduction of inflammatory mediator receptor antagonists into the joint, which prevent the inflammatory mediators within the joint from binding to their receptors and therefore preventing their deleterious effects.
Exercise and complimentary therapies (e.g. acupuncture, chiropractic, osteopathy, myofascial release techniques)
Controlled, appropriate exercise should form an integral part of the management of a horse with arthritis. Competition horses may need to be dropped down to a more appropriate level of competition if they are no longer able to comfortably perform at their current level.
All horses with arthritis require a good warm up (a minimum of 10 minutes walking) to allow for maximum lubrication and mobility of the joints prior to commencing more intensive schooling.
Complimentary therapies have been shown to have clinical benefits in the treatment and management of horses with arthritis, and are likely significant in maintaining range of motion through joint elasticity/flexibility, as well as encouraging optimal functioning of the supporting musculature, allowing the horse to compensate for any joint issues by recruiting his muscular system to appropriately distribute load and prevent overloading of any damaged tissues.
Modalities such as acupuncture have also been associated with pain relief (presumably due to the release of endorphins)
Above: Exercise (even gentle hand-walking) should form an integral part of the management of horses with osteoarthritis as it helps to maintain joint range of motion.
If your horse has arthritis and you want to discuss treatment options, please contact the clinic to book an appointment. You can email us at hello@capeequine.com.au or contact us by phone at 0467 485 976.
Reference List:
McIlwraith, C.W., Frisbie, D.D. and Kawcak, C.E. (2012) ‘The horse as a model of naturally occurring osteoarthritis’, Bone & Joint Research, 1(11), pp. 297–309. doi:10.1302/2046-3758.111.2000132.
McIlwraith, C.W. (2010) ‘The use of intra‐articular corticosteroids in the horse: What is known on a scientific basis?’, Equine Veterinary Journal, 42(6), pp. 563–571. doi:10.1111/j.2042-3306.2010.00095.x.
Marcella, K. (2012) Research points to pentosan polysulfate to treat equine osteoarthritis, DVM 360. Available at: https://www.dvm360.com/view/research-points-pentosan-polysulfate-treat-equine-osteoarthritis (Accessed: 07 January 2024).
Seabaugh, K.A. et al. (2022) ‘Examining the effects of the oral supplement biota orientalis in the osteochondral fragment-exercise model of osteoarthritis in the horse’, Frontiers in Veterinary Science, 9. doi:10.3389/fvets.2022.858391.
Loving, N.S. (2020) Polyacrylamide hydrogel for Intercarpal Osteoarthritis, EquiManagement. Available at: https://equimanagement.com/research-medical/polyacrylamide-hydrogel-for-intercarpal-osteoarthritis/ (Accessed: 07 January 2024).
Tnibar, A. (2022) ‘Intra-articular 2.5% polyacrylamide hydrogel, a new concept in the medication of equine osteoarthritis: A Review’, Journal of Equine Veterinary Science, 119, p. 104143. doi:10.1016/j.jevs.2022.104143.
Mayet, A. et al. (2023) ‘Systematic Review and meta-analysis of positive long-term effects after intra-articular administration of orthobiologic therapeutics in horses with naturally occurring osteoarthritis’, Frontiers in Veterinary Science, 10. doi:10.3389/fvets.2023.1125695.