- What is septic arthritis?
- Septic arthritis in children
- Other names for septic arthritis
What is septic arthritis?
Septic arthritis, also known as infectious arthritis or pyogenic arthritis, is a very rare condition caused by an infection in the joint. It is usually caused by bacteria, though it may be caused by other microorganisms. Incidence is about six per 100,000 of the population in any given year.
The condition can affect anyone but it is most common in those with underlying joint disease or prosthetic joints, and more common in older people and those with diabetes or a weakened immune system. Any joint may be affected, but septic arthritis is most common in the knee and hip, sometimes also occurring in the shoulder, elbow and ankle.
Symptoms usually develop quickly, over a few hours or days, and include pain, redness, swelling, heat and difficulty moving in the affected joint or joints. Many people will develop a fever. If the infection spreads, a person may also develop nausea, dizziness or drowsiness.
Septic arthritis occurs when infectious microorganisms reach the inside of the joints, most commonly entering the joints directly, for instance during joint replacement surgery. Infection in the bloodstream can also cause this condition if it spreads to the joints.
A diagnosis is confirmed when a fluid sample from the affected joint shows that bacteria or other infectious agents are present.
Septic arthritis is treated with antibiotics delivered into a vein, normally in a hospital stay of two weeks or more, followed by further antibiotics taken orally at home. Fluid may also be drawn from the infected joint using a needle and syringe.
Septic arthritis normally occurs in just one joint, but polyarticular septic arthritis, in which multiple joints throughout the body are infected, is also possible.
Good to know: It is very important to seek medical attention immediately if septic arthritis is suspected. The condition can rapidly cause irreversible joint damage and, left untreated, can be life threatening. However, with prompt treatment, most people will recover well.
Septic arthritis symptoms
- Redness of the overlying skin
- Stiffness and difficulty moving
- Inability to bear weight
In most people with septic arthritis, the onset of symptoms occurs very quickly, within a few hours or days. In about half of cases, the knee is affected. Other commonly affected joints include the hip, shoulder, elbow, ankle and, in the case of intravenous drug users, sternoclavicular joint between the collarbone and breastbone.
Septic arthritis causes
Septic arthritis is caused by bacteria entering the joint. This can occur indirectly by entering the body through, for example, a wound and traveling through the bloodstream to a joint, or by directly entering a joint, such as through injury or surgery.
As soon as bacteria invade the bloodstream, the body begins an immune response. White blood cells and joint lining cells may attempt to surround and digest the bacteria. The chemical signals sent out by these cells contribute to the characteristic inflammation of septic arthritis, which can cause destruction of cartilage. Depending on the infecting organism, the level of inflammatory response and joint destruction varies.
Most commonly, septic arthritis occurs in connection with a prosthetic joint (joint replacement). Prosthetic implant infection most often results from local infection, and may enter the joint during the joint replacement procedure. Bacteria may also enter the bloodstream at another site and travel to the joint, which may be more susceptible to infection as it heals.
- Age of 80 or above (45 percent of those affected are older than 65)
- Prosthetic implant, such as artificial knee or hip, or other recent joint surgery
- Prior joint damage, particularly from rheumatoid arthritis
- Cirrhosis (liver scarring due to conditions such as hepatitis and chronic alcoholism)
- HIV and AIDS or otherwise compromised immune system
- History of gout or other crystal-induced joint pain
- Recent blood infection
- Intravenous drug use
- A bone infection near to a joint
People with diabetes and weakened immune systems should seek prompt treatment for all infections, including urinary tract infections and skin infections.
Septic arthritis diagnosis
A diagnosis may be suspected based on symptoms and examination of the affected joints.
If a doctor suspects septic arthritis, they will immediately refer a person to the nearest emergency department for an assessment.
The diagnosis is confirmed when a sample of fluid from the joints reveals the presence of bacteria. Further diagnostic testing may include blood tests, an ultrasound, an X-ray, a CT scan or magnetic resonance imaging (MRI) of the joints.
Septic arthritis interview and physical exam
It is important that a person describe any joint pain and other symptoms, as well as how long they have been going on for.
A doctor will look for signs of septic arthritis, such as swollen, tender, warm joints with painful or limited movement and fever.
Septic arthritis laboratory tests
A blood test: This may reveal an elevated white blood cell count, which is normally found in cases of septic arthritis. Abnormally high levels of certain markers in the blood would also support a diagnosis that symptoms are caused by an inflammatory condition such as septic arthritis. Inflammatory markers which may be detected by a blood test include:
- C-reactive protein (CRP)
- Erythrocyte sedimentation rate (ESR or sed rate)
However, these tests come back normal in many cases of septic arthritis, so cannot be relied upon to rule out the condition.
Joint fluid aspiration: Joint fluid is drawn using a needle, and examined for the presence of infection to confirm diagnosis and to identify any organism found.
Septic arthritis medical imaging
A doctor may also recommend an X-ray, CT scan, ultrasound or MRI scan of the affected joint. This can help with diagnosis of septic arthritis and any complications. However, at an early stage of septic arthritis, there may not be any visible joint damage.
Septic arthritis treatment
- Antibiotics: Septic arthritis infection must be cleared with antibiotics delivered into a vein
- Draining the joint: This may be done to clear any infected fluid from the joint. This will either be done using a needle and syringe or by arthroscopy, in which a thin, metal tube is inserted through a small cut made near the affected joint.
- Pain relief: This is important to retain joint mobility
- Physiotherapy: Most people will require a lot of physiotherapy to maximize functioning of the joint after infection has cleared, to promote healing and prevent permanent muscle shortening
- In some cases, surgery: Occasionally, this may be done to clean the joints. If the septic arthritis followed a joint replacement surgery, the joint replacement itself may need removal.
Treatment normally involves a hospital stay of two weeks or more, followed by further antibiotics taken orally at home, normally for at least four more weeks.
Septic arthritis complications
- Osteomyelitis, a painful bone infection and inflammation
- Bone erosions, the loss of bone, caused by destructive joint inflammation
- Fibrous ankylosis, decreased range of motion, which may be caused by destruction of the joint lining
- Sepsis, also known as blood poisoning, in which the body attacks its own organs and tissues in response to infection. Sepsis can be life threatening
Good to know: It is very important to seek medical attention immediately if septic arthritis is suspected, to avoid serious complications. The condition can rapidly cause irreversible bone and joint damage and, left untreated, can be life threatening. However, with prompt treatment, most people will recover well.
Septic arthritis in children
Septic arthritis in children, also known as pediatric septic arthritis, is a very rare but serious emergency that must be treated promptly.
Signs and symptoms include:
- Inability to bear weight on the affected joint
Young children with septic arthritis are likely to be irritable and may cry if the infected joint is moved. They may also try to avoid using or putting any weight on an affected joint.
If a doctor suspects pediatric septic arthritis, they will immediately refer a child to the nearest emergency department for an assessment.
Treatment involves draining the joint, followed by intravenous antibiotics. Ongoing follow-up with an orthopedic surgeon is recommended to monitor and treat long-term effects, such as cartilage damage and growth disturbance. While these effects are rare, early diagnosis and intervention may improve long-term outcomes.
Other names for septic arthritis
- Infectious arthritis
- Pyogenic arthritis
- Suppurative arthritis
- Bacterial arthritis
- Infectious arthritis
- Fungal joint infection
- Bacterial joint inflammation
- Joint infection
Septic arthritis FAQs
Q: Is septic arthritis the same condition as reactive arthritis?
A: No, septic arthritis is not the same as reactive arthritis. In septic arthritis, infection is present within the joint. Reactive arthritis is an autoimmune response triggered by infection, but the infection is not located in the joint. Reactive arthritis generally lasts from a few weeks to a few months and, while its severity may vary, it normally resolves without serious complications. Septic arthritis can lead to disability and, left untreated, may be life threatening. In septic arthritis, the infection is treated with intravenous antibiotics. In reactive arthritis, oral antibiotics may be used to treat the triggering infection, but this does not shorten the duration of joint symptoms. For more information, see the resource on reactive arthritis.
Q: Osteomyelitis vs septic arthritis - what is the difference?
A: Osteomyelitis is infection of the bone, whereas septic arthritis is infection of a joint. Both may have similar causes, such as knife wounds or biting, and may spread through the blood from another location. Osteomyelitis and septic arthritis may also co-exist if, for example, infection spreads from the joint to the bone. Both conditions may have similar symptoms, such as pain in the affected area and fever, so can be mistaken for one another. Both conditions are rare, but can be life threatening if left untreated, so early diagnosis and treatment with drainage and intravenous antibiotics are important
Q: Septic arthritis vs gout - what is the difference?
A: Gout may present in a similar manner to septic arthritis, with acute pain, swelling, warmth, and decreased range of motion, normally starting in a single joint. However, both conditions have very different causes, treatments and outcomes. Gout is caused when there is buildup of uric acid in the blood that deposits urate crystals in a joint, causing a painful immune response, whereas septic arthritis is caused by infection in a joint. Septic arthritis may be life threatening if left untreated. Gout, while it may be acutely painful and, if it develops into a chronic condition, can cause joint damage, it is not life threatening. It is important to seek medical attention immediately, for appropriate treatment.
Medscape. "Advances in the Management of Bacterial Septic Arthritis." Accessed 23 June 2018. ↩
Patient.info. "Septic Arthritis | Symptoms and Treatment | Patient." Accessed 23 June 2018. ↩ ↩ ↩
BMJ Best Practice "Septic arthritis - Symptoms, diagnosis and treatment." Accessed 23 June 2018. ↩
AMBOSS. "Septic arthritis."](https://www.amboss.com/us/knowledge/Septic_arthritis) Accessed 23 June 2018. ↩