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What is septic arthritis?
Septic arthritis is an infection in a joint that can lead to serious pain and permanent damage. It requires immediate medical treatment.
Also known as infectious arthritis, septic arthritis is most commonly caused by bacteria.
- Through the bloodstream from an infection in another part of the body (such as the upper respiratory tract or urinary tract);
- From an injury at or near the joint, and;
- From surgery on the joint, including replacements with a prosthetic.
When the joint is infected, pus builds up, causing damage to the structures of the joint.
Factors that can increase the risk of developing septic arthritis include:
- Conditions that cause joint damage, such as rheumatoid arthritis, lupus, gout or osteoarthritis;
- Recent joint surgery;
- Having a prosthetic joint;
- An impaired immune system, which can be caused by other medical conditions (such as diabetes) or medications that suppress the immune system such as chemotherapy;
- Conditions that increase the risk of skin wounds, such as psoriasis and eczema;
- Alcoholism or injecting drugs, and;
- Untreated gonorrhoea.
Nongonococcal septic arthritis
This is septic arthritis that is caused by organisms other than Neisseria gonorrhoeae. A wide range of organisms can be the cause, but Staphylococus aureus is the most common.
It is more likely to occur in older people and young children. Knees and hips are the joints most likely to be affected.
Gonococcal septic arthritis
It is most common in younger, sexually active people, particularly:
- Young women during menstruation and pregnancy, and;
- Men who have sex with men.
Initially, people with gonococcal septic arthritis tend to experience pain that shifts through the joints such as the knees, ankles, wrists and elbows. Following this:
- Around 60% experience a form of inflammation called tenosynovitis (affecting the lining of tendons) that affect joints such as wrists, ankles, toes and fingers  , and;
- Around 40% experience an infection in one joint such as the knee, elbow or wrist  .
Most people with gonococcal septic arthritis also develop lesions on the skin of their extremities, particularly the palms of the hands and soles of the feet. These lesions often feature a number of small pustules.
Signs and symptoms
Symptoms of septic arthritis include pain, heat and swelling in affected joints. The skin over the joint may be red and the pain can be severe. Often, people with septic arthritis also get chills and fever, but this is not always the case.
The knee is the joint most commonly affected, but septic arthritis can also occur in the shoulder, wrist, hip and ankle and, less commonly, in other joints.
Symptoms usually develop within hours. Usually only one joint is affected, but more than one joint can be involved.
Methods for diagnosis
Tests used to diagnose septic arthritis include:
- Synovial fluid analysis. A sample of fluid from the space within the joint is withdrawn by needle, a procedure known as joint aspiration, and sent for laboratory analysis to identify the organism causing the infection, and;
- Blood tests to identify bacteria present in the bloodstream.
X-rays are generally not useful in detecting septic arthritis, but may be recommended to identify other potential causes of pain in the joint. An MRI may be recommended in cases where it is difficult to assess a joint (such as with the hip).
Types of treatment
A stay in hospital is usually required to treat septic arthritis.
Nongonococcal septic arthritis
High doses of antibiotics such as vancomyacin or ceftazidime are given intravenously. Treatment is usually started as soon as possible and may begin before the type of bacteria causing the infection is definitively identified.
The choice of antibiotic may depend on many factors. The antibiotic may later be changed to better target the infection once the bacteria is identified.
Once the infection has begun to improve, lower doses of antibiotics taken by mouth may be prescribed to ensure that infection clears completely from the joint.
In the much-less common case of a fungus causing the infection, antifungal medications will be used to treat the infection.
Drainage of the joint
Pus is drained from the joint to reduce damage while the antibiotics are fighting the infection. This may need to be repeated multiple times. Depending on the joint affected, drainage may be done with a needle, an arthroscope or, particularly with hip joints, open surgery may be required.
Infection in an artificial joint
If the infection occurs in an artificial joint, the prostheses may need to be removed in order for the infection to be treated. They can usually be replaced once the infection has settled down.
For the first few days, the joint may be placed in a splint because any movement of the joint is often very painful. However, splinting is usually only recommended for a short time.
Physiotherapy is very important to preserve function in the affected joint. Initially, exercises that maintain the range of motion of the joint can help recovery. When the infection has subsided, more strenuous exercises to strengthen the muscles around the joint may be recommended.
Gonococcal septic arthritis
This form of arthritis usually responds quickly to antibiotics (such as azithromycin and ceftriaxone) given intravenously.
If septic arthritis is not treated promptly, serious and permanent damage can occur to the joint leading to:
- A reduced range of movement in the joint, and;
- Chronic pain.
Treatment with antibiotics can cause side effects including nausea, vomiting and allergic reactions.
Prognosis depends on the type of organism that has caused the infection and how promptly it is treated.
People with gonococcal septic arthritis usually make a full recovery. Damage to the joint with nongonococcal septic arthritis tends to be more severe.
Practising safe sex can help to prevent gonorrhoea and gonococcal septic arthritis.