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, cancer, or infections.
This hereditary disorder is caused by abnormal development of the kneecap (patella). Displacement of the kneecap can be associated with multiple deformities of the hindlimb, involving the hip joint, femur, and tibia. Cats of any age can be affected.
Signs vary based on the severity of the displacement. In mild cases, lameness occurs infrequently, and 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. Veterinarians can often feel the displacement. X-rays can help your veterinarian see 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.
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. The condition is common in cats but it may not be noticed because cats often hide signs of pain. Approximately 60 to 90% of older cats have osteoarthritis.
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 weight loss (when appropriate), controlled exercise on soft surfaces, warm compresses of the affected joint, and the use of appropriate drugs to reduce pain and inflammation. Other treatments, such as joint fluid modifiers, may help prevent cartilage degeneration. 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.
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 rickettsiae and spirochetes.
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 help to confirm the diagnosis and identify the cause. Blood tests may also be necessary.
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.
The body’s own immune system can cause inflammation of joints (immune-mediated arthritis). 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 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, blood tests, 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. When diagnosed, spread of the cancer to the lungs has already occurred in about 25% of animals. Amputation of the limb is usually recommended to alleviate pain and, if possible, prevent spreading.
Several types of joint trauma can affect the joints in cats, including cranial cruciate ligament tears and palmar carpal ligament breakdown.
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 (meniscus) 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 excessive fluid in the joint and signs of arthritis. Testing of fluid removed from the joint or arthroscopy (examining the joint with a specialized camera) 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.
The shoulder, elbow, carpal (wrist), hip, stifle (knee), and tarsal (ankle) joints are those most commonly involved in fractures due to injury. In young animals, the portion of the bone where growth occurs—called the growth plate and usually located at the ends of the bones—is weak compared with adjacent bones, ligaments, and joint membranes, making this area more prone to injury.
Signs of joint fractures include lameness, pain, and joint swelling. If the injury affects an active growth plate, limb deformities can result. X-rays and computed tomography (CT) scans are used to confirm and locate the fracture.
The goal of treatment is to allow the fracture to heal in proper alignment while maintaining joint and limb functions. This is usually done by holding the fracture in place internally with pins, wires, or screws to stabilize it. The outlook for recovery is good as long as damage to the joint is not severe.
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 joint. 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.
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.
Also see professional content regarding arthropathies and related disorders in small animals.