Equine joint disorders

Osteoarthritis

Pathophysiology

Osteoarthritis (OA) is a noninflammatory disorder of joints characterized by degeneration and loss of articular cartilage and development of new bone on joint surfaces and margins. It can also involve sclerosis of the subchondral bone. OA is a common response of joints to a variety of insults. In general, it is seen as a “wear and tear” phenomenon but can also occur secondary to osteochondrosis and sepsis. Once cartilage starts to break down, several factors are released into the synovial fluid that cause further inflammation and further cartilage breakdown.

Diagnosis

Clinical signs associated with OA include pain on movement, reduced range of motion, increased joint fluid (effusion), and changes in the synovial fluid (less viscous, lower hyaluronan content). Generally, OA affects older horses, horses with a heavy work background, those with osteochondrosis, and those with previously septic joints. Diagnosis is based upon localized lameness (joint blocks) combined with radiographs and/or arthroscopy. Because OA starts as a cartilage disorder, not all lesions will be apparent radiographically.

Therapy

Cartilage does not heal well due to limited vascularity and potential for new cartilage growth.

At the present time we cannot resurface joints with normal cartilage. (Research is ongoing, funded by the NFL…). Treatment is aimed at slowing the rate of cartilage breakdown.

Surgical therapy

Arthroscopy is used not only as a diagnostic and prognostic tool but is also useful in treatment of OA. It is used to remove fragments of new bone and to clean up cartilage lesions and synovial proliferation (inflammatory response).

If the joint is unstable, it must be stabilized for any treatment to be successful. Remove or stabilize any loose fragments, debride any cysts. Without surgery in these cases, medications won’t help.

Pastern and lower hock joints may also be “arthrodesed” or fused. This prevents motion and therefore much of the pain associated. The pastern and lower hock are low motion joints so movement is limited already; decreasing movement is easier to obtain and does not affect other joints too severely. Fetlock and carpal joints are also occasionally arthrodesed. These are high motion joints so the fusion is much more complex and the complications greater.

Joint replacement is not commonly done in horses.

Medical management

Medical management is more often used due to the cost of arthroscopy and arthrodesis. Choices depend on many factors, including value of the horse, current performance and future performance expectations and the horse’s mental status (particularly if stall rest if recommened).

  • NSAIDs are used to inhibit the inflammatory reaction; however, they may also interfere with the healing process and should be used judiciously until their full effects are understood. Motion is good for joints so NSAIDs do help with encouraging horses to move around.
  • Corticosteroids may be injected into joints to relieve inflammation. At low concentrations they may be chondroprotective; however, prolonged use or high concentrations will cause cartilage degeneration. Methylprednisolone is typically used in low motion joints while triamcinolone is used in high motion joints.
  • Hyaluronan (HA) is frequently used in an attempt to provide cartilage structural materials, to increase the viscosity of the synovial fluid, and as a mild anti-inflammatory agent. An intravenous form (Legend®) is now available and there is some experimental data to support its use. It is probably most effective in cases of acute synovitis. It may need to be given weekly for optimum effects.
  • Polysulfonated glycosaminoglycan (PSGAG/ Adequan®) is composed principally of chondroitin sulfate, a component of cartilage. It is anti-inflammatory and is reported to stimulate the production of HA and to interfere with degradative enzymes. It may be given into the joint but greatly increases the risk of sepsis by decreasing the number of bacteria required to overwhelm the immune system. It is more often given im, with a manufacturer’s recommendation of treatment every 4 days for 7 treatments. 
  • Oral supplements have also been developed; chondroitin sulfate and glucosamine are the two most common components. Chondroitin sulfate is similar to PSGAGs in its activity; however, many (all?) forms of chondroitin sulfate are not biologically available. Glucosamine is a precursor of cartilage proteoglycans and may have a number of antiinflammatory activities. Experimental studies on these oral products are limited. The most convincing results have been with Cosequin®.  Other common and perhaps useful brands are FlexFree®, Synoflex®, and MSM®(oral form of DMSO). Tetracyclines are inhibitors of MMPs but use may compound drug resistance issues.  Neutraceuticals are NOT regulated by the FDA. 
  • IRAP (interleukin receptor antagonist protein) competes with interleukin 1 for receptor binding in an attempt to decreased inflammation. Duration of binding is unknown.
  • Free choice exercise helps keep joints mobile. Forced exercise can speed cartilage breakdown. Stall rest (if needed due to a particular therapy) can be very challenging for both horse and owner.
  • Frequent trimming helps to keep the toes short (best ) and to keep the foot balanced. 
  • Rehabilitation/physical therapies may be recommended. Not all are scientifically proven. These therapies include hydrotherapy, ice, swimming, acupuncture, chiropractic, laser, electrical stimulation, therapeutic ultrasound, counterirritants, radiation, shockwave, massage, and heat.
  • Nutrition/weight management. Weight control can be important. Supplements containing fatty acids may help decrease inflammation. Other supplements have variably shown anti-inflammatory and/or analgesic properties

Key Takeaways

Arthritis is common in horses and is usually due to wear and tear along with cartilage damage. Therapy is supportive

  • NSAIDs
  • Free choice exercise
  • Frequent hoof trimming
  • Supplements

Cartilage does not heal well. Joint supplements may be useful to prevent damage but quality varies.

Horse owners love fancy toys and “new” stuff (therapies).

Resources

Clinical insights: Recent developments in equine articular disease (2016–2018), Equine Veterinary Journal 50 (2018) 705–707

Pathophysiology of Osteoarthritis, CCE Jan/Feb 2009, pp 28-40

Management and Rehabilitation of Joint Disease in Sport Horses, Vet Clin Equine 34 (2018) 345–358

Evaluation of polysulfated glycosaminoglycan or sodium hyaluronan administered intra-articularly for treatment of horses with experimentally induced osteoarthritis. AJVR, 2009. DOI:10.2460/ajvr.70.2.203

Influence of trimming, hoof angle and shoeing on breakover duration in sound horses examined with hoof-mounted inertial sensors, Vet Rec 2021 – good explanation of  and how shoes impact it

License

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Large Animal Surgery - Supplemental Notes by Erin Malone, DVM, PhD; Elaine Norton, DVM PhD; Erica Dobbs, DVM; and Ashley Ezzo, DVM is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.