English
Degenerative joint disease (also called arthritis) refers to degeneration and loss of the articular cartilage in a horse’s joints.
Common triggers for arthritis include aging, traumatic injuries, and excessive use. Horses may develop symptoms such as joint swelling, reduced range of motion in the joint, and lameness.
There is no definitive treatment for arthritis, and the disease is progressive. Treatment primarily focuses on pain control and slowing the progression of disease. Common treatments include joint injections, anti-inflammatory medications, and rest from exercise.
The prognosis for degenerative joint disease varies depending on the severity of cartilage degeneration and the joint affected. Horses with equine arthritis require ongoing management and adjustment of treatment protocols for the remainder of life.
By working closely with veterinarians and other qualified bodywork practitioners, owners can ensure the best quality of life possible for their arthritic horses.
Degenerative Joint Disease in Horses
In horses, degenerative joint disease or osteoarthritis can develop in any joint, however it is most common in weight-bearing joints found in the limbs.
Normally, articular cartilage protects the bones on either side of a joint from rubbing against each other. [1] In horses with arthritis, the cartilage degenerates and the bones contact each other, resulting in grinding of the bone surfaces and pain. [1]
Arthritis in horses usually occurs from one of two scenarios: abnormal cartilage experiencing normal stresses, or normal cartilage experiencing abnormal stresses. [1]
Abnormal Cartilage
Abnormal joint cartilage is any cartilage unable to withstand a normal workload. In affected horses, the joint cartilage sustains damage when even mild forces are applied during use of the joint. [2]
This damage activates enzymes (proteins that break down tissue) within the joint, resulting in further cartilage damage. [2]
Common examples of abnormal joint cartilage include osteochondrosis, a developmental defect of joint cartilage, and aging.
Osteochondrosis
In osteochondrosis, the joint cartilage fails to completely cover the bony surfaces within the joint or produces wavy or indented cartilage that does not glide smoothly. [1]
Interaction of these defects during movement of the joint can damage the cartilage, triggering inflammation and arthritis. [2]
Aging
With aging, several changes occur that compromise the function of joint cartilage. Major changes include: [3]
- Thin cartilage unable to withstand extreme forces
- Increased activity of enzymes that break down cartilage
- Reduced activity of healing and repair products in the joint fluid
- Poor synthesis of new cartilage to replace damaged tissue
The combination of these factors results in weak cartilage that is unable to repair small injuries, making the joint more likely to develop arthritis even under normal use. [2]
Abnormal Stresses
Abnormal stresses on joint cartilage can result from injuries to the joint and its surrounding structures, or from excessive use of the joint. [2]
Injuries
Injuries, such as bone fractures, ligament tears, or tendon damage, can affect the stability of nearby joints, causing irregular or erratic movement (joint laxity). [2]
When unstable joints are used, there is a risk of the cartilage surfaces contacting each other, causing abrasions or irritation. [2]
Abrasions from joint laxity can damage chondrocytes, the cells that make up cartilage. [2] Chondrocyte damage activates enzymes that break down tissues and results in loss of key structural components of the cartilage. [2]
Loss of cartilage tissue resulting from chondrocyte damage eventually leads to arthritis. [2]
Excessive Use
Excessive use of a joint can also result in chondrocyte damage and loss of cartilage structure. [2] Exercise can produce microtrauma within cartilage, microscopic injuries that must be repaired by the joint’s repair mechanisms. [2]
Under most circumstances, microtraumas are quickly repaired and the joint continues normal function. [2] With excessive joint use, microtraumas accumulate faster than the cartilage is able to repair them. [2] Eventually, continued chondrocyte injury activates degrading enzymes, which initiates inflammation and arthritis. [2]
Horses with the highest risk of excessive joint use are those used for disciplines with frequent high-impact weight bearing events. [2] Example disciplines include racing, jumping, and barrel racing, where the joints experience a large amount of concussive force as the horse performs. [2]
Effects of Cartilage Degeneration
Once joint cartilage is damaged, it activates inflammation, which leads to further damage within the joint. [2]
The cycle of cartilage damage triggering inflammation leading to further cartilage damage results in progressive destruction until there is no joint cartilage remaining. [2]
Inflammation can also cause secondary effects in the joint itself and the tissues surrounding it. [1] The main outcomes of degenerative joint disease are: [1]
- Pain
- Joint swelling
- Reduced range of motion
- Changes in joint fluid consistency
- Alterations in bone composition within the joint
Pain
Cartilage does not have nerve endings, however the bones and soft tissues surrounding the joint do. [1] The inflammatory response associated with arthritis produces proteins that activate these pain-sensing nerves. [1] As a result, horses with cartilage degeneration feel pain from flexing the joint or during movement. [1]
An additional contributor to pain from arthritis is disruption of the periosteum, the connective tissue that covers bones. [1] The periosteum contains a large network of nerve endings that can be disrupted by bony proliferations associated with advanced arthritis. [1]
Affected horses can develop high levels of pain from osteophyte (new bone tissue) development for this reason. [1]
Joint Swelling
Inflammation makes blood vessels in the affected area leaky, causing increased fluid accumulation in the joint. Leakage into the joint also increases the concentration of anti-inflammatory proteins in the affected joint. [1] These factors combined result in joint swelling.