The condition known as septic arthritis is different from ordinary arthritis as most people understand it. While the term arthritis, as it is conventionally used, refers to pain and inflammation in the joints, septic arthritis is a bacterial infection in the joint cavity, usually caused by staphylococcus aureus bacteria (in layman’s terms, a staph infection).

While it occurs more often in the knee than in other joints, septic arthritis in the ankle is not uncommon.

It can occur at any age, but when it occurs in children it is most often seen in children under the age of 3. It is also sometimes called suppurative arthritis due to the pus that often accompanies bacterial infection.

This condition is a medical emergency, and if you experience any of the symptoms described here you should see a doctor immediately. In an infant, it can be recognized by the child’s behavior—the baby may cry whenever the affected foot is moved or touched.

Symptoms of Septic Arthritis in the Ankle To Look For

Septic arthritis in the ankle is usually accompanied by:

• Severe pain
• Swelling
• Redness
• Warmth emanating from the joint
• Fever

It is the combination of these symptoms that most strongly suggests an infection of this type—particularly the fever and the warmth of the ankle.

Causes and Risk Factors for Septic Arthritis

As noted above, the most common cause of septic arthritis in the ankle is staph infection. Good health and personal hygiene do not rule it out; staphylococcus bacteria are everywhere, and they can live even on the skin of a healthy person.

The synovial membrane that lines your joints is ill-equipped to fend off infections, and your body reacts to the problem by inflaming the surrounding tissue, which reduces blood flow and increases pressure, thereby making the problem worse.

Other types of bacteria can also cause septic arthritis. Candida bacteria can even cause chronic septic arthritis, although this is rare.

Fungal infections are also a possibility. Regardless of the type of microorganism that causes it, this condition occurs when the bacterial or fungal agent responsible gets to the affected joint via the bloodstream, often because of direct injury to the ankle.

In rare cases, the infection can be contracted during surgery (or afterward, if the surgeon’s post-operative wound-care instructions are not followed correctly).

Factors that can increase the risk of this condition include:

• Existing bacterial infection elsewhere in the body (e.g., a respiratory infection), which can spread to the joint through the bloodstream
• Prosthetic joint implants. Ankle joints are particularly susceptible—the infection rate for them is about 9%. If this happens, the joint implant will most likely need to be removed.
• Certain chronic illnesses, including diabetes, or any disease that weakens the immune system
• Existing problems with the ankle joint, such as gout, rheumatoid arthritis, or osteoarthritis
• Medication for osteoarthritis, rheumatoid arthritis, and other conditions: Any medication that suppresses the functioning of the immune system can make you more susceptible to infection, and immunosuppressive drugs are sometimes used to treat some forms of arthritis that occur when the immune system attacks the synovial membranes.
• IV drug use (heroin, for example). People who use illegal drugs sometimes risk infection by sharing unclean needles.
• Recent arthroscopic surgery
• Recent ankle injury

In sexually active young adults, gonorrhea is one of the most common causes of this kind of infection.

Progression and Complications of Septic Arthritis

If septic arthritis in the ankle is left untreated, it can cause degeneration in the joint, leading to permanent damage.

Diagnosis and Treatment of Septic Arthritis

If your doctor suspects septic arthritis, he or she will insert a needle into the joint cavity and withdraw a small sample of the synovial fluid (the fluid that fills all joint cavities), for analysis.

Blood tests will also be performed in order to look for the presence of certain bacteria in your bloodstream. An x-ray of your ankle may also shed light on the problem.

Once the problem has been diagnosed, it can be treated. The bacterial infection will be addressed with antibiotics, which will be administered intravenously at first; later you will be given oral antibiotics to take (be sure to follow your doctor’s instructions for these).

It will also be necessary to drain the infected synovial fluid from the joint. This may be done with a needle, or with arthroscopic surgery, which involves a tiny video camera at the tip of a small, flexible tube that also carries tiny surgical instruments.

While you are recovering from your surgery, you may find that you experience side effects from the antibiotics you are taking, including nausea and diarrhea. Be sure to inform your doctor if this happens, and he or she may be able to find a different antibiotic that does not affect you quite so strongly.

What is the Prognosis for Septic Arthritis?

If treatment is administered promptly with antibiotics, the prognosis is excellent. In some cases the situation may be complicated—for example, a prosthetic implant may need to be removed and possibly re-implanted at a later date—but most patients recover from septic arthritis with minimal long-term damage if the problem is diagnosed before the infection has a chance to do serious harm.