What do I need to know about Arthritis?

Arthritis is inflammation of a joint which causes pain and stiffness.

Related conditions including degenerative joint disease (DJD), osteoarthritis (inflammation involving bone changes), synovitis (inflammation of the synovium, i.e., joint lining), are often called 'arthritis'.

How Does Arthritis Occur?

Normal, painless joint function is essential for an athletic animal and for this to occur, each component of the joint structure must be healthy and working properly. Smooth movement of the opposing bone ends relative to each other, and the surrounding structures is achieved by its complex structure:

  • The special shape of the end of each bone

  • The covering of smooth cartilage over the end of each bone

  • The presence of synovial fluid ('joint fluid') which lubricates the cartilage

  • All contained within the joint capsule which forms an elastic pouch that encloses the structures of the joint and in some cases contains supporting ligaments

Diagram of a simple joint to show these structures:

Arthritis is Interference

Arthritis occurs when there is interference with normal structure and function

Damage to the cartilage and/or the bone through trauma (injury) or infection results in roughening of the smooth surfaces. Movement of the roughened bone ends and/or damaged cartilage results in inflammation, producing inflammatory mediators that alter the synovial fluid, all of which causes swelling of the joint, pain, and restriction of movement. This initial response is called acute arthritis.

Injury to the joint capsule and its ligaments can also trigger inflammation resulting in thickening of the capsule, reducing its elasticity, and thinning of the joint fluid, reducing its lubricating ability.

Chronic Arthritis

Over time, new bone is formed in response to surface damage. This new bone is rough and is not covered with protective cartilage, therefore interferes with joint movement, and causes pain. These longer-term effects are called chronic arthritis.

Degenerative Joint Disease

Degenerative joint disease can result in the same long-term changes but in contrast to true arthritis, is usually not associated with pain or inflammation in the early stages.

In DJD the joint structures respond to wear and tear by gradually changing shape and elasticity. Many horses with early DJD are still sound, but these changes typically progress to a stage where the horse develops lameness.

What are the Signs of Arthritis in Horses?

Joint inflammation increases the amount of fluid in the joint and this usually causes visible and/or palpable bulging of the joint capsule (e.g., 'bog' spavin, 'popped' knee, 'windgall').

However, not all joint swellings are due to arthritis. In arthritis, there is pain when the affected joint is flexed (bent) and the horse may be lame or stiff at the walk or trot. In acute arthritis, the swollen joint may feel warm to touch.

Acute Arthritis

In acute arthritis caused by infection ('septic' arthritis) there is usually severe inflammation, pain, and lameness. If not quickly controlled, this condition can cause severe destruction of joint surfaces that may end a horse's athletic career and may even necessitate euthanasia on humane grounds. Septic arthritis must therefore be treated as a medical emergency. Infection may be introduced directly by injury (joint puncture) or via the bloodstream from a primary focus of infection elsewhere.

Chronic Arthritis

With DJD and chronic arthritis, joint mobility is reduced but there may not be pain on flexion of the joint. There may be lameness which has gradually worsened over time or lameness which improves with exercise, i.e., the horse 'warms up'.

In cases where there is multiple joint involvement, the horse may appear generally stiff all over. In an older horse, the main sign of abnormality may be difficulty in standing up after a period of lying down.

How is the Diagnosis of Arthritis Confirmed?

If you are worried that your horse might have arthritis, you should ask your veterinarian to examine him. This will involve:

  • Feeling the limbs to look for abnormalities such as swelling, reduction in range of movement or pain on flexion. In acute arthritis, the joint may be hot and swollen.

  • Examining for lameness or stiffness. This might mean just walking and trotting in hand if the lameness is obvious but if the gait abnormality is only subtle, the horse may need to be ridden or lunged 

In many cases, it is not possible to confirm the diagnosis or its significance by clinical examination alone. Further examinations may involve:

  • Nerve block examinations, where local anaesthetic is injected around specific nerves in the leg to determine the source of pain

  • Radiographic and fluoroscopic (x-ray) examinations to rule out fractures and to look at the bones at the joint surfaces for signs of injury, degeneration, or abnormality

  • Ultrasound examination of joint surfaces and soft tissues

  • Joint fluid collection for laboratory analysis to look specifically for signs of infection

How is Arthritis in Horses Treated?

Conservative Treatment

Some horses with acute inflammation respond simply to rest and anti-inflammatories for a period of weeks to months. In most cases, this will mean that the horse is confined to a stable. Do not be tempted to turn the horse out during this time. Even though you are not riding him, he could still gallop or leap about and cause more damage to the inflamed structures.

 Oral joint supplements that include glucosamine are recommended. Intra-muscular injections of Adequan or intravenous injections of hyaluronic acid may be prescribed.

Joint Injections

In some cases of arthritis, it may be necessary or useful to inject medication into the joint itself. The more commonly used intra-articular preparations are corticosteroids, hyaluronic acid, and Adequan. These reduce inflammation within the joint and help re-establish the normal lubricating properties of the joint fluid.

While this treatment is often initially effective, some cases require repeated injections. 

Surgery

Where there has been extensive new bone formation or where a chip fracture has occurred as a consequence of DJD, arthroscopic surgery may be helpful to give the joint a better chance for recovery.

If, in spite of all efforts, severe chronic arthritis remains and the horse has a persistently painful joint with little movement, it is sometimes possible to restore soundness by surgically fusing the affected joint. This is occasionally used for the pastern and lower hock joints but only as a last resort after all other forms of treatment have been tried.

Overall

The choice of appropriate therapy must be based upon an accurate and complete diagnosis and the needs of the individual case. Your veterinarian will help you with this.

What is the Prognosis?

If a case of acute arthritis that is diagnosed and successfully treated early, a complete cure may occur, leaving no residual abnormality.

If the inflammation does not respond to treatment and/or is complicated by infection or cartilage or joint injury, new bone may form, and the joint may be permanently affected by chronic arthritis. If controlled by careful management and appropriate treatments, this may not cause lameness with its associated pain and restricted mobility.

Caution

It is important to realize that a horse can have arthritic changes which are visible on radiographs but may still move soundly and be able to compete successfully. Also, it is possible for a horse to suffer from arthritis, involving the cartilage and joint fluid that will not produce demonstrable radiographic changes.

Both scenarios can produce difficulties when a horse is being examined for purchase, i.e., 'vetted'. If radiographs are taken as a requested routine part of a pre-purchase examination, the images must be carefully interpreted with reference to the findings of the clinical examination.