Some joint diseases, such as arthritis, affect the joint membranes themselves. Other types of joint conditions affect the tendons, cartilage, bursae, and fluid within the joint. Joint disorders may be congenital (present at birth) or may be the result of injury to the joint, abnormal development, immune-related conditions, or infections.
Displacement of the Kneecap
This hereditary disorder is caused by abnormal development of the kneecap (patella). Displacement of the kneecap is often associated with multiple deformities of the hindlimb, involving the hip joint, femur, and tibia.
Signs vary widely based on the severity of the displacement. In mild cases, the kneecap can be manually displaced but easily returned to normal position. As displacement becomes more severe, the dislocated kneecap is more often out of place, the limb is consistently lame, and bone deformities may be seen. X-rays can help your veterinarian see how severely the kneecap is displaced and what effects this has had on the limb.
There are several surgical options for treatment, depending on the severity of the displacement. Cats are less severely affected than dogs and have an excellent outlook for recovery.
Hip dysplasia is an abnormal development of the hip joints. It is rare in domestic cats but occurs more commonly in purebred cats. It is characterized by a loose hip joint that eventually leads to degenerative joint disease (osteoarthritis). Signs of hip dysplasia vary, and lameness may be mild to severe. Most cats require no surgical treatment; however, lifestyle changes such as weight reduction may help reduce discomfort.
Osteoarthritis (Degenerative Joint Disease)
The joint cartilage in freely moving joints may degenerate over time, leading to loss of joint movement and, in many cases, pain. Joint degeneration can be caused by trauma, infection, the body's own immune system, or malformation during development. This leads to inflammation of the joint membrane, continued cartilage destruction and inflammation, and abnormal joint function. Although more commonly diagnosed in dogs, this condition does occur in cats. It may not be noticed because of differences in the lifestyles of cats and dogs.
Signs of osteoarthritis include lameness, joint swelling, wasting away of muscle, thickening and scarring of the joint membrane, and a grating sound during joint movement. X-rays show increased fluid within the joint, soft-tissue swelling around the joint, the formation of bony outgrowths, hardening and thickening of bone beneath the cartilage, and sometimes a narrowed joint space.
Treatments can be either medical or surgical. Medical therapy may include the use of appropriate drugs to reduce pain and inflammation. Surgical options include joint fusion, joint replacement, cutting of the joint, and amputation. The outlook for recovery depends on the location and severity of the joint disease. Other treatments, including weight reduction, carefully monitored exercise on soft surfaces, and the use of joint-fluid modifiers, may help prevent further cartilage degeneration.
Infectious, or septic, arthritis is usually caused by bacteria that spread through the blood or enter the body as a result of trauma (with penetrating wounds) or surgery. Other causes of septic arthritis include rickettsia and spirochetes. see Infections: Introduction to Infections
Signs of septic arthritis include lameness, swelling, pain of affected joint(s), fever, listlessness, loss of appetite, and stiffness. X-rays may reveal increased fluid within the joint in early cases and degenerative joint disease in longterm conditions. Laboratory tests on fluid removed from the joint may be useful in confirming the diagnosis.
Treatment consists of antibiotics administered by mouth or intravenously, flushing of the joint cavity, and surgical removal of dead, damaged, or infected tissue in severe cases.
Arthritis caused by the body's own immune system can cause inflammation of joints. It generally affects several joints. In some types of immune-mediated arthritis, joint cartilage and bone beneath the cartilage is destroyed. Feline progressive polyarthritis, which resembles rheumatoid arthritis in people, is an example of the type of arthritis that destroys joint cartilage and bone beneath the cartilage. Systemic lupus erythematosus (see Immune Disorders of Cats: Systemic Lupus Erythematosus (Lupus)) is the most common form of arthritis that causes inflammation of the joint without destruction of cartilage and bone. This condition may affect other organ systems, including the skin.
Signs of immune-mediated arthritis include lameness, pain and swelling in multiple joints, fever, a general feeling of illness, and persistent loss of appetite. These signs commonly come and go. In addition to signs, the diagnosis is aided by x-rays, biopsy of joint tissue, and examination of joint fluid (commonly called a joint tap).
Treatment involves anti-inflammatory medications and chemotherapeutic drugs. The outlook for recovery is uncertain. Relapses are relatively common and the cause of the reactions is often unknown.
This type of arthritis is most commonly caused by a tumor known as a synovial cell sarcoma. It is the most common cancerous (malignant) tumor involving the joints. Signs include lameness and joint swelling. X-rays show soft-tissue swelling and a reaction around the bone. A biopsy reveals evidence of a soft-tissue tumor. Spread of the cancer to the lungs occurs in about 25% of animals; thus, amputation of the limb is usually recommended to prevent spreading.
Several types of joint trauma that can affect the joints in cats, including cranial cruciate ligament tears and palmar carpal ligament breakdown.
Cranial Cruciate Ligament Tear
Tearing of the cranial cruciate ligament of the knee joint (stifle) is usually caused by serious injury. However, injuries are more likely to occur when the joint structure is already weakened by degeneration, the animal's own immune system, or defects in conformation of the joint. Most injuries involve a tear in the middle of the ligament, although some result from bone separation at the origin of the ligament. A tear of this type can make the knee unstable and can lead to cartilage injury, buildup of joint fluid, bony outgrowths, and hardening and thickening of the joint membrane.
Signs include lameness, pain, joint swelling, fluid buildup, and a grating sound when the joint is moved. In addition, the joint may appear to be abnormally loose. Partial tears are characterized by a reduced ability to move the joint, especially bending it. X-rays may show the injury and/or damage to the joint; testing of fluid removed from the joint may also be used to help diagnose the condition.
Both medical and surgical treatment options are available. Physical therapy, weight reduction, and nonsteroidal anti-inflammatory drugs ease discomfort from inflammation and degenerative joint disease. The outlook after surgery is good as long as degenerative joint disease has not progressed too far.
Palmar Carpal Ligament Breakdown
Injuries sustained when falling or jumping can cause hyperextension, in which the limb extends beyond its normal range of motion. This produces excessive force on the wrist (carpus), which can cause tearing of the palmar carpal ligaments and fibrocartilage, leading to collapse of the joints. This is a rare problem in cats. Signs include lameness, swelling of the carpal joint, and a characteristic stance in which the heel is touching the ground. For mild cases a splint or cast may be sufficient, but surgery is usually required. Surgery involves fusing the affected joints using a bone plate and screws, pins and wires, or an external system. The outlook for recovery is good.
Dislocation of the Hip
Hip dislocation is usually the result of injury or trauma that displaces the head of the femur from the socket of the hip joint. Signs of hip dislocation include lameness, pain during movement of the hip joint, and a shortened limb. X-rays are useful in confirming the dislocation and revealing the presence of fractures. Nonsurgical treatment involves forcefully moving the joint back into place (closed manipulation) and using slings to keep the hip in its normal position. Surgical treatment involves stabilization using sutures or pins. Surgical resection of the bones involved or total hip replacement may be performed if more conservative treatment has not succeeded. The outlook for recovery is usually excellent.
Last full review/revision July 2011 by Russel R. Hanson, DVM, DACVS, DACVECC; Joerg A. Auer, DrMedVet, Dr h c, MS, DACVS, DECVS; Joseph Harari, MS, DVM, DACVS; Dale A. Moore, MS, DVM, MPVM, PhD; Sheldon Padgett, DVM, MS, DACVS