Arthritis Infective

Septic arthritis, Infectious arthritis

Infectious arthritis is a serious joint infection that can rapidly damage cartilage and bone within days if left untreated, but with prompt treatment, most people can make a full recovery.

Table of contents

• What is infectious arthritis?
• What causes this condition?
• Who is affected?
• Signs and symptoms
• How is it diagnosed?
• Treatment options
• What to expect

What is infectious arthritis?

Infectious arthritis, also known as septic arthritis, is a painful infection in a joint that happens when germs spread to one or more of your joints and cause inflammation^[1][2]. The inflammation affects the surface of the cartilage (a type of connective tissue) that lines your joints and the synovial fluid that lubricates your joints^[2].

This is a serious medical condition that requires immediate treatment. Without proper care, the infection can quickly and severely damage the cartilage and bone within the joint, sometimes within just 24 to 48 hours of the infection starting^[5]. The good news is that with prompt treatment, this is usually a curable form of arthritis^[3].

Most cases of infectious arthritis affect only one joint, although in rare cases multiple joints can become infected^[2][17]. The knee is the most commonly affected joint, but the infection can also occur in the hip, shoulder, ankle, wrist, and other joints^[1][5].

• Knee
• Hip
• Shoulder
• Ankle
• Elbow
• Wrist

What causes this condition?

Infectious arthritis is caused by an infection from bacteria, viruses, or fungi that reaches a joint^[2]. The infection-causing germs can enter a joint in several ways^[3]:

• Spreading through the bloodstream from another part of the body, such as the lungs during pneumonia
• Through a nearby wound
• After surgery, an injection, or trauma
• Through a penetrating injury, such as an animal bite

The most common cause of infectious arthritis is bacteria, particularly Staphylococcus aureus (staph), which is a bacterium that often lives on healthy skin^[2][5][17]. Other bacteria that can cause the infection include Streptococcus species, Haemophilus influenzae, and in sexually active individuals, Neisseria gonorrhoeae (which causes gonorrhea)^[3][6].

In children under 2 to 3 years of age, Kingella kingae is the most common bacterial cause^[13]. People with certain conditions, such as sickle cell disease, may be at risk for infection with Salmonella species^[13].

Viral infections can also cause infectious arthritis, and these cases often resolve on their own without specific treatment^[3][17]. Fungal infections are less common but can occur, especially in people with weakened immune systems or those on prolonged antibiotic therapy^[6].

Who is affected?

Infectious arthritis is not very common. There are approximately 2 to 6 cases per 100,000 people per year^[2]. However, certain groups of people are at higher risk^[4][5]:

Children more commonly experience septic arthritis than adults. In fact, approximately 50 percent of children with joint infection are under 3 years of age^[2]. People born male between 2 and 3 years of age are most likely to get septic arthritis^[2].

Adults at increased risk include those who are older than 80 years, particularly older adults who may have more health conditions^[5]. People with the following conditions or situations face a greater risk^[4][5]:

• Rheumatoid arthritis or other forms of inflammatory arthritis
• Diabetes
• A weakened immune system, including HIV infection
• Recent joint surgery or a prosthetic joint (such as a knee or hip replacement)
• Skin infections
• Use of immunosuppressive medications, including corticosteroids
• Injection drug use
• Cancer
• Chronic medical illnesses such as lung disease or liver disease
• Gonorrhea (a sexually transmitted infection)

Signs and symptoms

Symptoms of infectious arthritis usually develop quickly over a few days and need to be checked straight away^[4]. The most common symptoms include^[1][2]:

• Severe pain in the affected joint, which often starts suddenly
• Swelling and warmth around the joint
• Redness of the skin around the joint
• Difficulty moving the affected joint or limited range of motion
• Not wanting to use or move the affected joint
• Fever, feeling hot and shivery, or chills

More than 50 percent of patients with septic arthritis have a history of joint swelling, joint pain, and fever^[5]. In children, symptoms may also include being grouchy or irritable, loss of appetite, vomiting, sore throat, or headache^[6].

If you have an artificial joint, such as a knee or hip replacement, signs and symptoms may be different. Minor pain and swelling may develop months or years after the surgery. The joint may also loosen, causing pain while moving or putting weight on it. The pain typically goes away when at rest, but in severe cases, the joint may become dislocated^[1].

You should see a doctor immediately if you have severe joint pain that started suddenly, or if you feel generally unwell with a high temperature and joint symptoms^[1][4].

How is it diagnosed?

Diagnosis of infectious arthritis includes a complete medical history, physical examination, and laboratory tests^[17]. Before starting antibiotic therapy, it is important to obtain and analyze synovial fluid from the affected joint through a procedure called arthrocentesis^[5].

The fluid sample is tested for^[6][7]:

• White blood cells and bacteria
• Gram stain to help identify the type of bacteria
• Cultures to grow and identify the specific organism causing the infection
• Crystal analysis to rule out other types of arthritis

Blood tests may also be done to look for bacteria and signs of infection in the blood^[6]. Your doctor may order additional tests such as^[6][7]:

• X-rays to assess damage to the joint
• Other imaging tests to look for changes in the joint or to check for loosening of an artificial joint
• Tests of phlegm, spinal fluid, and urine to look for bacteria and find the source of infection

Treatment options

Treatment for infectious arthritis involves two main approaches: draining the infected joint fluid and giving antibiotics^[7][17].

Draining the joint

Removing the infected joint fluid is crucial because a septic joint should be considered a closed abscess, and antibiotic treatment alone should not be expected to resolve the infection^[10]. This can be done in several ways^[7][17]:

• Joint aspiration: A needle is inserted into the joint space to withdraw fluid. This is the least invasive method.
• Arthroscopy: A flexible tube with a video camera is placed in the joint through a small incision. Suction and drainage tubes are then inserted through small incisions around the joint.
• Open surgery: Some joints, such as the hip, are more difficult to drain with a needle or arthroscopy and may require an open surgical procedure.

Antibiotics

After synovial fluid has been obtained, antibiotic therapy should be started immediately if there is clinical concern for septic arthritis^[5]. Initial treatment is chosen to cover the most likely bacteria, particularly Staphylococcus aureus and Streptococcus species^[5]. Once the specific organism is identified from cultures, the antibiotic can be adjusted to target that specific germ^[7].

Antibiotics are usually given through a vein in the arm at first. Later, you may be able to switch to oral antibiotics^[7]. Research shows that oral antibiotics are not inferior to intravenous antibiotics for treatment of septic arthritis^[5].

You will usually be treated in hospital with antibiotics given straight into a vein, and you will probably have to take antibiotic tablets for several weeks after you leave hospital^[4]. The average hospital stay is about 2 weeks, and most people start feeling better quickly once they are given antibiotics^[4].

The total duration of antibiotic therapy ranges from two to six weeks, though certain infections require longer courses^[5]. For example, septic arthritis caused by methicillin-resistant Staphylococcus aureus (MRSA) should be treated with drainage or debridement and 14 days of intravenous antibiotics followed by oral antibiotics, totaling three to four weeks of therapy^[5].

It is very important to keep taking the antibiotic tablets for as long as you are told to, even if you feel better. Stopping treatment too soon could lead to the infection coming back^[4].

Other treatments

Infectious arthritis caused by a virus usually goes away on its own with no specific treatment, and fungal infections are treated with antifungal medication^[17].

In addition to treatment prescribed by your doctor, it is important to rest and protect the inflamed joint^[17]. You may be referred to a physiotherapist to help you get the joint moving again after the infection has been treated. This should help prevent any long-term stiffness in the joint^[4].

If the infection was in an artificial joint, the joint may need to be removed. It may be possible to replace it with a new artificial joint once the infection has been treated^[4].

What to expect

Although infectious arthritis is rare, it is a serious condition that can cause permanent damage to the affected joint and other complications. It can also cause death if it is not treated^[2]. If the infection is not treated, it can spread to other parts of the body, a condition called sepsis, which is life-threatening^[2].

However, when diagnosed and treated promptly, most people can make a full recovery^[4]. Early diagnosis and treatment are crucial for preserving joint function and preventing permanent joint damage^[5][13].

The long-term outlook depends on how quickly treatment begins. If appropriate antibiotic therapy is not started within 24 to 48 hours of onset, there can be permanent problems including bone loss beneath the cartilage, cartilage destruction, and permanent joint dysfunction^[5].

Be sure to see your healthcare provider or go to the nearest hospital immediately if you experience symptoms of infectious arthritis^[2].