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Joint Effusion (Swelling)

By: Dr.Douglas Brum

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Joint effusion may be a sudden (acute) occurrence or a long-standing (chronic) problem. Many times, acute joint swelling is the result of trauma and usually involves only a single joint. External wounds may be noted and the animal is usually lame and painful at the swollen joint. Chronic joint distention may or may not be associated with lameness. The most common cause of chronic distention is degenerative osteoarthritis and may occur in multiple joints. Many animals with this type of joint effusion are more lame after lying down or first thing in the morning. Typically, the lameness improves over the course of the day.

One of the most important observations to make when dealing with joint effusion is if the dog is feeling ill. Animals feeling ill may be lethargic, anorexic, febrile, and they commonly have multiple joints that are affected. Reluctance to walk or even get up is a common complaint. Systemic illness should be expected in ill animals with joint effusion.

Ill animals may often require extensive diagnostic testing before a definitive diagnosis can be made. On the other hand, dogs with acute or chronic joint effusion that are still feeling fairly well are more likely to have conditions that are easier to diagnose. In these dogs a definitive diagnosis can often be achieved by a good history, physical exam and perhaps a radiograph. Rarely, animals with joint effusion will not have obviously distended joints and require arthrocentesis and cytologic evaluation of the joint fluid for diagnosis.

Another important part in evaluating an animal with joint effusion is whether or not there are multiple joints involved (polyarthritis). Animals with polyarthritis may walk very stiffly or have shifting leg lameness. Polyarthritis is a systemic disease that may be acute or chronic and it usually causes an animal to feel ill. Some dogs with polyarthritis have recurrent episodes making diagnosis more difficult. Since there are many causes of joint effusion an accurate diagnosis is crucial for correct treatment.


Joint effusion is caused by an increase in fluid within the joint space. The amount of fluid within the joint can vary greatly, from a visually imperceptible amount to a very distended joint. In all cases of joint effusion, the fluid in the joint is abnormal in either cell type or viscosity (thickness). In many cases, the evaluation of the joint fluid is needed to determine the cause of the effusion. Joint fluid analysis may suggest a specific disease. Many times a simple history may identify the cause of the effusion. Traumatic injury, history of degenerative osteoarthritis, breed and age of the dog, and a travel history are all important in the assessment of joint effusion. The general causes of joint effusion include:

  • Trauma. A traumatic injury to a joint usually causes an acute joint swelling and lameness. The injury may be a soft tissue injury with joint swelling the result of inflammation or bleeding into the joint. Fractures of the bones involving the joint can also lead to severe joint effusion and pain. If a wound penetrates the skin and enters the joint, a bacterial (or septic) infection can result, leading to joint swelling, fever and pain.

  • Chronic degenerative joint disease or osteoarthritis. Commonly known as just "arthritis," it is generally seen in older animals with a history of intermittent or chronic lameness. The joint swelling can result from an increase in joint fluid due to chronic inflammation or an actual increase in bone size due to bony proliferation around the joint. Joint viscosity decreases as chronic intermittent inflammation causes an increase in joint size with time. Typically, the joint swelling develops very slowly; however, a minor traumatic injury to a previously arthritic joint may cause an acute severe effusion.

  • Infectious joint disease. There are many causes of infectious joint disease that can cause a joint effusion. Septic bacterial infections can either be from an external wound or be spread by the blood from another area of the body. Typically only one joint is affected. Other types of effusions caused by infectious agents usually involve multiple joints and may be associated with other symptoms. Tick borne diseases including Lyme disease, Rocky Mountain spotted fever, and ehrlichiosis are more commonly being diagnosed within certain geographic areas. Dogs with these diseases are usually quite ill from additional metabolic dysfunction that might include bleeding problems, vasculitis (inflammation of blood vessels), kidney disease, and neurologic impairment.

  • Immune mediated polyarthritis. Numerous immune disorders may cause joint effusion. Many times this will be associated with other signs of illness. Immune mediated polyarthritis may cause either an erosive (causing bony destruction of the articular bone) or non-erosive arthritis. Causes of erosive polyarthritis include: rheumatoid arthritis and erosive polyarthritis of greyhounds. Non-erosive causes of polyarthritis include: systemic lupus erythematosus (SLE), idiopathic (unknown cause), drug and vaccine reactions, and polyarthritis secondary to other chronic inflammatory, infectious or cancerous conditions.

  • Certain breeds are associated with breed specific polyarthropathies (disease and effusion of multiple joints). Greyhounds, usually under two years, may develop an erosive (bone deforming) polyarthritis (multiple joint inflammation) of their distal extremities. The shar-pei breed may develop a disease called "shar-pei fever," categorized by fevers and swellings of the hock and carpal joints. Over time, severe kidney disease (renal amyloidosis) may develop. Akitas, boxers, Weimaraners, Bernese Mountain dogs, German shorthair pointers and beagles have been known to develop a polyarthritis or a polyarthritis/meningitis (inflammation of the spinal cord) syndrome that affects young dogs.

  • Clotting abnormalities. Occasionally animals with clotting abnormalities have acute bleeding into a joint. This is called hemarthosis. Most of the time, this is related to a minor traumatic injury that under normal circumstances would not cause a problem, but when a tendency to bleed is also present, a bloody joint effusion may form. Some causes of clotting problems include: thrombocytopenia, hemophilia, rodenticide intoxication, and von Willebrand's disease.

  • Tumors of the joint capsule or bone. Tumors that involve the joint capsule most commonly a synovial cell carcinoma can cause joint effusion. A single joint is affected and it generally occurs in middle-aged to older dogs. Other tumors of the bone around the joint space can occasionally cause effusion and joint swelling.                

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