Joint Infections (Septic Arthritis) in Cats

Key Takeaways

Septic arthritis (SA) is rare in cats and is described as joint inflammation triggered by infection. 

• SA occurs when a joint becomes infected by a bite or puncture wound 

• Rarely, infection spreads through the bloodstream and infects multiple joints

• Symptoms include sudden onset lameness, swelling of one or more legs, poor appetite, lethargy and fever

• Diagnosis involves physical examination, blood work, culture of joint fluid, and diagnostic imaging

• Treatment includes pain relief, high dose antibiotics and some cases require surgical flushing of the joint under anesthesia

• Prognosis depends on severity and speed of treatment 

• Cases receiving early treatment usually recover quickly, whereas treatment delays sometimes result in damage to the joint surface, irreversible osteoarthritis, and sepsis

A Closer Look: What is SA in Cats?

Septic Arthritis (SA) is a rare, but serious condition resulting in pain and dysfunction of the affected limb.

Prognosis depends on the speed of diagnosis and start of treatment and the degree of damage to the articular cartilage (joint surface). Cartilage damage increases with delayed treatment which can result in: 

• Osteoarthritis 

• Osteomyelitis (bone infection)

• Sepsis

These cases require intensive, long-term care and may have a poor prognosis. 

Cats with suspected SA require prompt veterinary treatment.

Risk Factors

Symptoms of SA vary depending on the underlying disease mechanisms.

Single joint SA usually results from an infection in the joint from an external source, such as a bite or injury. These cases often require treatment of the wound as well as the joint infection itself. Joints most commonly affected include the hip, knee, ankle, and wrist.

Multi-joint infections are more likely to be caused by spread through the bloodstream from other organs such as the bladder, kidneys, heart, teeth, and skin. 

Severe or untreated infections sometimes result in sepsis. Symptoms include:

• Poor appetite

• Weight loss

• Lethargy

• Fever

• Rapid breathing

Neutering male cats reduces fighting behavior, which may reduce the risk of SA. Outdoor cats are at higher risk of SA due to increased risk of penetrating wounds.

Possible Causes

SA results from a single joint becoming infected. Some cases of SA result from the infection spreading to the joint through the bloodstream and can occur in one or multiple joints.

There are multiple causes of SA including:

Bite wounds caused by fighting with other animals, including cats.

Puncture wounds caused by 

• Broken glass 

• Thorns

Injury resulting in exposure of the joint surface caused by

• Car accidents 

• Dog attacks

Medical treatment such as 

• Joint surgery 

• Injections into the joint

Infection as a result of spread through the bloodstream can originate anywhere else in the body but commonly includes:

• Bladder or kidney infection

• Skin infection

• Heart valve infection

• Dental disease

Main Symptoms

Symptoms of SA include:

• Sudden onset, severe lameness of one or more limbs

• Palpable swelling 

• Joint pain

• Lethargy

• Poor appetite

Testing and Diagnosis

Diagnosis of SA involves:

• Physical examination

• Blood work

• X-rays

• CT scan

• Biopsy of the joint capsule

In addition to examination of joint fluid such as:

• Bacterial culture

• Microscopic examination

Steps to Recovery

Treatment options include:

• Pain relief

• Antibiotics 

• Hot and cold compresses

• Surgical flushing of the joint

• Physical therapy

Treatment of sepsis, if present, includes:

• Antibiotics

• Fluid therapy

• Nutritional support

SA is a serious condition which takes many weeks to resolve. Prognosis varies depending on speed of diagnosis and onset of treatment.

Cats with a traumatic injury that is rapidly diagnosed typically require 6-8 weeks of antibiotics, their prognosis is generally good and most cases recover fully.

Delayed treatment allows more time for the infection to cause damage to the joint, and is associated with a poorer prognosis. Severely affected cases of septic arthritis that recover often develop irreparable osteoarthritis, requiring lifelong management.

Cats with multiple joint involvement often have an underlying blood infection. Cats that develop sepsis often recover but require prolonged hospitalization and extensive treatment.

Prevention

Prevention of SA is not possible, however, with rapid diagnosis and appropriate treatment prevention of long term complications is possible. Maintaining an indoor-only lifestyle reduces risk of penetrating injuries which can result in SA.

Is SA Common in Cats?

SA is uncommon in cats.

Typical Treatment

• Pain relief

• Antibiotics 

• Hot and cold compresses

• Surgical flushing of the joint

• Exercise management

• Treatment of sepsis

• Fluid therapy

• Nutritional support