Degenerative Joint Disease

Roman Lamberski

Ruth Ann Lobos

Dr. Daniel J. Burba

Degenerative joint disease (DJD), also known as osteoarthritis, is a common problem seen with horses that have excessive wear and tear on their joints. This can be initiated by training on hard surfaces, excessive training, direct trauma to the joint, or infection in the joint. It could also be due to inherent problems of the horse such as poor conformation, abnormal cartilage formation, and poor nutrition. This can be a devastating disease that, as of now, has no cure.

Causes:

Two major factors control the development and progression of DJD: biomechanical forces and biochemical substances. The biomechanical forces are the excessive forces that the horse puts on its joints through repetitive stress and strain during exercise. The biochemical damage occurs when enzymes are released into the joint, resulting in the breakdown of the joint cartilage. This leads to more enzymes being released, causing further cartilage damage resulting in a self-perpetuating destructive cycle. Cartilage in the joints is made up of cells known as chondroctyes and a matrix of proteins. These cells have a very limited ability to regenerate, resulting in irreversible cartilage destruction.

Joints Involved:

The joints that are usually affected are the lower joints of the legs because they are the major shock absorbers. In the forelimb, it is usually the carpus (knee). In the hind limb it is commonly the hock, also know as bone spavin. In the coffin joint it is called low ring bone and in the pastern it is known as high ring bone. The horses will show signs of lameness and pain with flexion of the involved joints. There is commonly swelling in the affected joint; and if the process has been ongoing, there will be a decreased range of flexion.

How DJD Is Diagnosed:

The involved joint can be pinpointed using nerve and joint blocks. The main diagnostic tool used in conjunction with the presenting signs is radiography. There can be several different changes that appear on the radiographs. This may include bone spur formation, destruction of the underlying bone, and also narrowing of the joint width from the loss of the cartilage. If the latter of the changes occurs, this indicates advanced stages of DJD and worsens the prognosis for soundness. However, it should be noted that the changes on the radiographs do not always correlate with the clinical signs as some horses compensate better than others.

Treatment:

It is important to understand that there is no cure for DJD and that all of the therapy is aimed at slowing the progression of the disease and alleviating the clinical signs. For cases that present with a sudden onset of lameness, the best treatment is bandaging to control joint swelling and stall rest. After 2-3 days of rest, hand-walking the horse will help in repair of some of the damage to the joint. If there is a large amount of swelling, the use of oral anti-inflammatory drugs (i.e. bute) will help to reduce the swelling and decrease the pain. When dealing with more chronic DJD, the therapy is aimed at slowing the progression of this self-perpetuating disease. In order to reduce the swelling, non-steroidal anti-inflammatory drugs (i.e. bute) can be administered orally for 1-2 weeks. If there is a large amount of swelling, intra-articular corticosteroids may be needed. Long term therapy with corticosteroids is not usually prescribed due to potential side effects on the joint. When the joint capsule is inflammed, as it often is with DJD, an abnormal consistency of the fluid occurs; therefore, the cartilage that is present in the joint won’t be properly nourished. To help with this, hyaluronic acid can be injected into the joint every two to four weeks. It is important to understand that there are several different forms of the acid on the market, and as with other products the higher quality formulations cost more but have better proven results. To slow down the destruction of joint cartilage by the previously discussed enzymes, the use of intra-articular or intra-muscular injections of polysulfated glycosaminoglycans (PSGAG’S) are often performed. These substances decrease the detrimental effects of the enzymes on the jount cartilage, thus protecting the remaining cartilage.

There are also products on the market called neutraceuticals, which are oral supplements that claim to help regenerate and replace the damaged cartilage. One such example is Cosequinã. There are no studies as of now that accurately evaluate their effects.

Summary:

The best way to control DJD is to prevent it. Unfortunately, due to the fact that this disease is often secondary to a traumatic incident, the prevention is difficult. However, there are several areas of care that can help reduce the possibility of developing DJD from an injury. A diet with balanced vitamins and minerals and the correct ratio of roughage to grain should be formulated to help with the proper development of cartilage. The conformation of the limbs when the horse is a foal will greatly influence the way the joint will wear as he matures. If there is not proper alignment, there could be abnormal wear leading to premature DJD of the joint. Hoof care is an area that is often overlooked but has a lot to do with the proper alignment of the lower pastern region. Adequate trimming and shoeing can help maintain alignment. Finally the training regime must be reasonable for the animal. It is important that the training ground is level and that the surface is not too hard or too soft. Each animal should have a work schedule tailored to its unique fitness level and injury status. Adequate muscling will help reduce the likelihood for injury and thus reduce the chances for DJD.

There is no cure for DJD. All the therapies are aimed at slowing its progression and alleviating the pain and swelling involved. Therefore, the prognosis for this disease is not good.