Septic Arthritis in Cats

Vets explain septic arthritis as an illness started by one of several bacteria, fungi or the feline calicivirus. Conditions such as diabetes, Addison’s disease, past penetrating injuries, an intra-articular injection or an existing osteoarthritis can make a cat more prone to this condition.

Septic arthritis is caused by a bacteria that causes infections, disease, and abscesses within the joints and tissues in cats. The bacteria and sepsis develop inside one or more joints in the cat’s body. This infection causes the characteristic joint inflammation known as arthritis. While septic arthritis is common in dogs, it’s much rarer in cats. Several different kinds of bacteria can lead to the development of septic arthritis. Feline calicivirus and fungal agents can also cause this condition.

A cat who has developed septic arthritis will be in obvious pain, not feeling well:

• Pain in the affected joint or joints
• Loss of appetite
• Fever
• Stiffness
• Listless and sluggish
• Lame (acute or chronic)
• Joint or joints are swollen
• Affected joints are hot to the touch
• Poor range of motion in affected joint or joints

The causes of septic arthritis are varied, ranging from infection to injury or existing arthritis:

Infection:

• Bacteria entering the cat’s bloodstream
• Rickettsia spp. (Rocky Mountain spotted fever)
• Spirochetes (causes Lyme disease)
• Ehrlichiosis (Ehrlichia)
• Pasteurella bacteria
• Staphylococci
• Coliform bacteria
• Streptococci
• Bacteroides
• Propionibacterium
• Fusobacterium
• Peptostreptococcus
• Feline calicivirus
• Mycoplasma
• Leishmania
• Blastomyces
• Coccidioides
• Cryptococcus

Any one of the above bacteria or viruses can enter the cat’s body after a penetrating injury or surgery, leading to the development of septic arthritis.

Some cats may live with one or more risk factors, which include:

• Hypoadrenocorticism or Addison’s disease
• Drug therapy that suppresses the cat’s immune response
• Diabetes mellitus
• Disease
• Existing bony arthritis or osteoarthritis
• Pre-existing damage to the joint or joints
• Steroidal intra-articular injection (into the joint space)
• Past trauma that penetrated the affected joint or joints

The vet who suspects septic arthritis observes the cat’s symptoms, such as lameness. They will take a complete history, asking the cat owner about past animal fights, injuries or illnesses that could have initiated the septic arthritis. 

Vets run several lab tests, including a complete blood count (CBC), biochemistry profile and urinalysis. If the vet has already begun to suspect septic arthritis, they will order X-rays, allowing them to look for any changes to the cat’s joints. If the vet sees unusual or abnormal bone formations, bone destruction or irregular joint spaces, this leads them to narrow the diagnosis down, but they aren’t done yet.

The cat will be anesthetized and fluid will be removed from the affected joint or joints. The vet is looking for an abnormal amount of fluid in these spaces, a high numbers of inflammatory cells, an unusual color to the fluid and, if the cause of the cat’s illness is bacterial, any bacteria that may be present. 

Culturing the joint fluid allows the illness-causing microorganisms to develop in the lab, which helps the vet to make a firm diagnosis. It’s vital to get an accurate diagnosis as soon as possible to help the cat make a full recovery. If the vet finds more white blood cells, such as neutrophils, the diagnosis is more certain.

Once the vet has confirmed a diagnosis of septic arthritis, the cat begins taking antibiotics, either through an IV or by mouth. Depending on how persistent the bacterial infection is, the cat may need to be on an antibiotic long-term. It’s vital for the cat to take its entire course of antibiotics. These may include amoxicillin or cephalosporin.

Anti-inflammatory medications (NSAIDS) may also be prescribed to reduce pain and inflammation. Pain medications may be prescribed to help control the cat’s pain.

The joint cavity will be flushed to remove infectious agents (this is known as “joint lavage”).  This helps to minimize the extent of the injury in the cat’s joint or joints.

The vet may also choose to immobilize the cat’s limb to improve its level of comfort. If this is done, it should only be for a short time.

If the infection and arthritis are long-standing, the cat will undergo surgery to remove the debris within the joint (debridement). The joint will be cleaned and, after that is done, the vet places a catheter or drain to allow the joint to continue draining. While the cat is under treatment, the vet will take samples of the fluid being removed by the catheter. This allows them to track the cat’s recovery from infection.

The vet may opt for arthroscopy, which enables them to inspect the joint close-up. This process also allows the vet to target treatment as well.

Hot and cold packs will be placed on the joint, both in the hospital and at home. This helps to promote blood flow to the area and helps to reduce swelling, which allows the cat to begin recovering. While the cat is recovering, it will be kept on restricted activity until all of its symptoms have been resolved. Cage rest may be necessary.

If the cat’s septic arthritis (acute) is diagnosed within 24 to 48 hours, its response to antibiotic therapy should aid in a good recovery. Bacteria resistant to antibiotics or a delayed diagnosis makes the cat’s recovery more difficult to obtain. This form of bacteria is called a virulent organism and makes the cat’s prognosis guarded to poor.

The cat may suffer from long-term degenerative joint disease, which is a kind of arthritis. Here, the cartilage within the joint begins to break down, causing significant symptoms and pain. The cat may develop stiff joints and limited range of motion.

Bacterial (or fungal) infections could come back; or the cat could develop a generalized, body-wide infection or sepsis. If infection goes into the bone, this is known as osteomyelitis. The cat’s owner should be on the lookout for a recurrence of the bone infection, because quick diagnosis gives the cat a better chance of recovery.

Some cats may need to go through physical therapy to help regain normal joint movement, maintain the health of the cartilage in its joints, and to prevent the contraction of the muscles close to the infected joints.