Some joint disorders, such as arthritis, affect the joint membranes themselves. Other types of joint conditions affect the tendons, cartilage, bursae, and fluid within the joint (synovial fluid).

Arthritis

Arthritis refers to inflammation in a joint. All joint diseases that affect large animals produce some degree of inflammation, often with accompanying swelling, pain, redness or heat.

Important arthritic conditions include traumatic arthritis, osteochondritis dissecans, subchondral cystic lesions, septic (infectious) arthritis, and osteoarthritis.

Traumatic Arthritis

Traumatic arthritis includes inflammation of the synovial membrane and joint capsule, chip fractures within the joint, tears (sprains) of ligaments or cartilage near or within a joint, and the gradual loss of cartilage of the joints known as osteoarthritis. It may be seen in any horse but typically occurs in horses that are athletes. A similar condition occurs in human athletes that undergo traumatic or repeated injury of a particular joint, such as the knee.

In its early stage, excess fluid enters injured joints, which can make the surrounding tissues swollen and warm. In more severe cases, manipulation of the joint causes pain. The chronic stage includes a general thickening and scarring of connective tissue, which reduces the range of joint motion. The horse's gait may change mildly, or it may become severely lame.

Veterinarians take x-rays to exclude other traumatic conditions, such as bone disease or fractures in bone or cartilage. Examination with an endoscope may be necessary to exclude tearing of ligaments or cartilage in the leg joints.

Treatment of traumatic joint inflammation includes rest and physical therapy regimens such as cold water treatment, ice, passive bending of the joint, and swimming. Nonsteroidal anti-inflammatory drugs are routinely prescribed to relieve pain and inflammation; corticosteroids may be recommended in some cases. In more severe cases, a veterinarian will flush the joint with water to remove any inflammatory or cartilage debris. This is more effective than joint drainage alone.

Arthroscopic surgery may be recommended to remove fragments of bone and cartilage (most commonly seen in the carpus and fetlock) to minimize the ongoing development of osteoarthritis. After such surgery, 2 to 6 months of rest follows, with physical therapy during the recovery period. The success rate in returning horses to previous performance levels is high if the degeneration is minimal at the time of surgery.

Osteochondritis Dissecans

In osteochondritis dissecans, the immature joint cartilage separates from the underlying bone. Fluid enters the space, and cysts may form under the cartilage. The cartilage may break away completely or, if the joint is rested or protected, reattach itself to bone. Osteochondritis dissecans usually is seen in young animals (less than 1 year old), most commonly at the femoropatellar (knee) joint, tarsal joint, fetlock joints, and the shoulder. The exact cause is unknown but contributing factors likely include a genetic predisposition in the animal, rapid growth, high caloric intake, disproportionate levels of copper and zinc in the diet, and hormonal factors (see Bone, Joint, and Muscle Disorders in Horses: Osteochondritis Dissecans).

Cysts beneath the Cartilage (Subchondral Cysts)

Cysts beneath the cartilage, called subchondral cysts, occur in the femorotibial joint and in the fetlock, pastern, elbow, shoulder, and distal phalanx of horses. Lameness is the usual sign. Levels of excessive joint fluid vary, so the diagnosis is usually made on the basis of the location of lameness and the responsiveness to pain within the joint. X-rays are necessary to confirm the diagnosis.

Surgery using an arthroscope is currently recommended in the femorotibial joint whenever a complete cyst is present. Smaller cysts are treated conservatively at first. Athletic soundness is achieved in 65 to 70% of these horses. More recently, some horses have been treated with an injection of corticosteroids.

Surgery is usually recommended for cysts beneath the cartilage in the fetlock. Single cysts associated with the pastern and elbow joints are treated conservatively and have a fair outlook for recovery. If possible, surgery is recommended for cysts of the distal phalanx because results with conservative treatment are very poor.

Septic Arthritis

Infectious, or septic, arthritis is usually caused by bacterial infection in a joint. Infection may occur after a traumatic injury, surgery, or injections, or it may enter the joint through the bloodstream. A common example of bloodborne infection is called navel ill, in which the infection reaches the foal through the umbilical cord. Infections in a horse's digestive tract or lungs can also travel to a joint through the blood.

Septic arthritis usually produces severe lameness and swelling of the joint. When fluid from the joint is obtained and examined, it is cloudy and contaminated. In foals, the infection often inflames the bone and bone marrow.

Septic arthritis must be treated promptly to avoid permanent damage. Infections are treated with injectable broad-spectrum antibiotics, as well as antibiotics injected directly in the joint. Nonsteroidal anti-inflammatory drugs may be prescribed as well. Other useful therapies include flushing the joint with saline solution and cleaning and draining the joint with an endoscope. The effectiveness of treatment is monitored carefully by watching for signs and repeating the examination and analysis of the joint fluid.

Osteoarthritis

Osteoarthritis, which is sometimes called degenerative joint disease, is a progressive deterioration of the joint cartilage. It represents the end stage of most of the other diseases discussed above, such as traumatic arthritis involving the synovial membrane and joint capsule, joint fractures, traumatic damage to cartilage, osteochondritis dissecans, cysts beneath cartilage, and infective arthritis.

Osteoarthritis produces lameness. There may be varying degrees of excess fluid in the joint, an abnormal thickening and scarring of the membranes, and restricted motion of the involved joints. X-rays show decreased joint space, bony outgrowths, inflammation of the muscles or tendons, and a hardening and thickening of the tissue below the cartilage. In less severe cases, an endoscope is used to observe the degree of joint damage.

Treatment of osteoarthritis is generally limited to reducing joint pain and stiffness. Nonsteroidal anti-inflammatory drugs (for example, firocoxib, ketoprofen, and phenylbutazone) or corticosteroids may provide relief. Physical therapy may prove helpful. In advanced cases, surgical fusion may be performed on selected joints. Some horses return to athletic soundness following surgical fusion of the pastern or tarsal joints. For very valuable animals, the fetlocks may be surgically fused, making the horse comfortable and capable of breeding.

Bursitis

A bursa is a small fluid-filled sac between a tendon and a bone (or other tissues that rub against one another) that reduces friction around the joint. Common in horses, bursitis is an inflammatory reaction within a bursa that can range from mild inflammation to infection. True bursitis involves inflammation of a natural bursa, for example, fistulous withers. In contrast, acquired bursitis is the development or inflammation of a bursa where none previously existed, as with capped elbow or hock.

Bursitis may develop suddenly with swelling, warmth, and pain, or it may persist over a long time with excess fluid and generalized thickening. Chronic bursitis often develops as a result of repeated trauma, abnormal thickening and scarring of connective tissue, and other longterm changes. The cold, painless swellings associated with chronic bursitis do not severely interfere with joint function unless they are greatly enlarged.

Infective bursitis is more serious and may produce pain and lameness in the joint. Infections may begin locally following an injection or travel from elsewhere to the bursa through the bloodstream.

Bursitis pain may be relieved with cold packs, by draining the bursal sac, or by directly medicating the bursa. (Repeated injections, however, pose a risk of infection.) Chronic bursitis is treated with surgery. Treating infective bursitis requires injectable antibiotics as well as drainage of the infected area.

Fistulous Withers and Poll Evil

Fistulous withers is the name of a condition in which the bursa in a horse's withers region (the ridge between the shoulder bones) becomes infected and inflamed. Poll evil is a virtually identical condition, except that the location of infection is the bursa behind the horse's ears in the area known as the poll. In each instance, a ruptured bursal sac creates an opening that makes the bursa susceptible to infection. Both conditions are rare.

Both fistulous withers and poll evil may be caused by trauma or an infection. Infections frequently are caused by Brucella abortus bacteria. If tests reveal the presence of Brucella, owners should be aware that this bacterium can be transmitted to people. Outbreaks of brucellosis in cattle have occured after contact with horses with open bursitis.

The inflammation caused by fistulous withers and poll evil thickens the bursa wall. The bursal sacs swell and may rupture if unprotected. In more advanced cases, nearby ligaments and the tips of the vertebral spines are affected, sometimes causing the death of these tissues.

The earlier treatment is started, the better the outlook for recovery. The most successful treatment is complete surgical removal of the infected bursa. However, the cost of treatment required in longterm cases often exceeds the value of the animal, and the risk of human infection (in cases in which Brucella is involved) should be carefully considered. It is prudent to keep horses separated from Brucella-infected cattle, and to keep cattle separated from horses with discharging fistulous withers.

Capped Elbow and Hock

Capped elbow and hock are acquired forms of bursitis. Bursas beneath the hock and elbow can become inflamed if a horse suffers trauma from falling in or kicking its stall, from lying on poorly bedded hard floors, riding a trailer tailgate, wearing iron shoes that project beyond the heels, or from leaning or reclining for long periods of time.

Capped elbow and hock rarely cause lameness, but fluid-filled swellings may develop on and around the affected bursa. The bursa may be soft at first but is soon surrounded by a fibrous capsule, especially in the case of a recurrent, older injury. The amount of initial swelling may vary. Infection may occur in chronic cases.

If detected early, the condition may respond well to applications of cold water, followed in a few days by fluid drainage and a corticosteroid injection. The bursa may also be reduced in size by ultrasonic radiation therapy. Another method involves the application of a substance called a counterirritant that irritates the skin and thereby reduces the inflammation of the bursa. Older bursas are more resistant to treatment. Surgery is recommended for advanced longterm cases or when infection is present. If a capped elbow has been caused by the heel or the shoe, a shoe-boil roll should be used to prevent reinjury. For a capped hock, modifying the horse's behavior so it does not kick the stall may offer the only hope of a permanent solution.

Tendinitis

Tendinitis is the inflammation of a tendon. Tendon inflammation may be short-term (acute tendinitis), or build up over a period of time (chronic tendinitis). The condition is most common among horses that do fast work, such as racehorses. The flexor tendons are generally involved, and the forelegs are more likely to be affected than the hind legs. The condition ruptures the tendon fibers to varying degrees. Blood vessels are also ruptured, and fluid may accumulate in the affected area.

Tendinitis usually appears after a horse is exercised improperly. Contributing factors may include fatigue or overextension, poor conditioning, and poor racetrack conditions. Tendinitis also develops when horses are trained despite prior inflammation of the tendon. Improper shoeing increases a horse's vulnerability to tendinitis, as do any malformations of the joints.

Horses with acute tendinitis are severely lame, with affected joints that are hot, painful, and swollen. In chronic tendinitis, fibrous tissues around the tendon join together, thicken, and scar. The horse may appear sound while walking or trotting but becomes lame again when put to a gallop. Your veterinarian may use ultrasonography to locate defects or injuries that are otherwise undetectable.

Horses with acute tendinitis should be stall-rested. Swelling and inflammation should be treated aggressively with cold packs and anti-inflammatory drugs; however, corticosteroid injections directly into the tendon are not recommended. Depending on the amount of damage, inflamed tendons may need to be supported and immobilized. In some cases, tendon splitting is recommended to decrease pressure within the tendon due to fluid or blood buildup. Recently, bone marrow injections that introduce stem cells and growth factors have produced encouraging results.

Rehabilitation following tendinitis should include a regimen of increasing exercise. Regardless of treatment, the outlook for full recovery in a racehorse is guarded.

Tenosynovitis

Tenosynovitis is an inflammation of the synovial membrane and usually the outer fibrous covering of the tendon. Possible causes include a response to traumatic injury or infection. When seen in young animals where the cause is uncertain, the condition is called idiopathic synovitis.

Lameness and swelling of the tendon sheath varies depending on severity of the condition. Where infection is involved, the horse will be very noticeably lame. Longterm tenosynovitis is common in the tendon coverings near the hock and fetlock.

In cases where the cause is unknown, no treatment is recommended initially. When inflammation is severe, cold packs, nonsteroidal anti-inflammatory drugs, and rest may relieve the signs. In more chronic cases, counterirritants and bandaging may be tried. Radiation therapy may be helpful. Infective tenosynovitis requires whole-body antibiotics and drainage of the affected site.

Last full review/revision July 2011 by Russel R. Hanson, DVM, DACVS, DACVECC; Joerg A. Auer, DrMedVet, Dr h c, MS, DACVS, DECVS; Andrew P. Bathe, MA, VetMB, DACVS, DEO, MRCVS; Leo B. Jeffcott, MA, BVM, PhD, FRCVS, DVSc, VD; Svend E. Kold, DMV, MRCVS, RCVS Specialist in Equine Surgery (Orthopedics); C. Wayne McIlwraith, BVSc, PhD, DSc, FRCVS, DACVS; Dale A. Moore, MS, DVM, MPVM, PhD; Sheldon Padgett, DVM, MS, DACVS; Tracy A. Turner, DVM, MS, DACVS, DABT; Stephanie J. Valberg, DVM, PhD, DACVIM; John F. Van Vleet, DVM, PhD