Authors

 Dr Keran Sundaraj MBBS MSc (Trauma) FRACS FAOA

Septic arthritis is an infection in a joint. Infections may be acute (presenting within hours to days) or chronic (days to weeks), and prompt diagnosis and treatment may prevent significant ongoing illness.

Presentation

Commonly patients will present with a severely painful joint even at rest. The joint is swollen, and pain with movement is a hallmark feature. 

Due to the infection, patients may feel unwell with fevers, sweats and chills. 

Causes

Infection in the joint can come from trauma or injury directly into the joint space or indirectly via the bloodstream from an injury or infection elsewhere (eg. urinary tract infection, skin cut, food poisoning etc). 

Risk factors for developing septic arthritis include:

• Age (young or very elderly)

• Medical conditions

  • Diabetes

  • Rheumatoid arthritis

  • Liver failure

  • Immunocompromised patients

• Recent surgery

Tests

Bloods

• The white cell count and inflammatory markers (CRP) can help determine the degree of inflammation within the body. The CRP can be used as a guide to monitor the infection.

X-rays

• X-rays can rule out other causes of pain, such as arthritis, fracture, or foreign body.

CT

• CT imaging can visualise other structures around the joint such as fluid collections.

MRI

• MRIs are not first-line investigations in joint infections. However, they are used if there is a poor response to treatment or unclear diagnosis.

Aspiration

• Fluid from the joint is collected to look for infection.

• A needle is placed into the affected joint. An ultrasound or CT may be used to guide the needle into the correct position.

• This is the most beneficial test in diagnosing a septic joint. The fluid from the joint is cultured to identify the bacteria and the appropriate antibiotic for the infection. Preliminary results will be back within hours, but final results (include the antibiotic 'sensitivities' may take days).

Treatment

Initial

• Patients are admitted to the hospital when treating a septic joint. This allows for pain relief and close observation of the patient.

• Patients with a joint infection may become unwell quickly. Occasionally, close monitoring in an intensive care unit is necessary.

Antibiotics

• Antibiotics are started after a sample of joint fluid is obtained.

• Infectious Disease Specialists determine the choice of antibiotic and the duration. Antibiotics are often given via an intravenous (IV) line over 2 to 6 weeks.

• A patient may be able to receive antibiotics at home if a PICC line is inserted. Unlike a regular canula, this IV line can stay in for several weeks.

• Depending on the bacteria, and the patient's health, oral antibiotics may be necessary for weeks to months after the initial IV antibiotic course.

Surgery

• Most septic joints require the joint to be 'washed out' of bacteria. Depending on the joint involved, this may either be a keyhole or open surgery.

• Sometimes a tube is placed to help drain any remaining bacteria.

• Occasionally, this surgery may need to be repeated. This is determined by the patient's symptoms (pain) and blood tests (such as CRP).

Complications of Septic Arthritis

The majority of patients improve to relatively normal function after treatment for septic arthritis. However, in some instances, the bacteria may damage the cartilage surfaces leading to arthritis. For some patients, the progression to arthritis may be rapid.

Treatment for post-infection arthritis can be challenging. End-stage arthritis is usually treated with joint replacement. However, this may be extremely risky if there are any remaining bacteria. Therefore, very rarely, a staged operation with an antibiotic loaded-cement spacer is used before the definitive metal and plastic joint is implanted.

What to Discuss with Dr Sundaraj

• How long can I expect off work?

• When can I start driving?

• When can I start physiotherapy?

• How long do I need to be on antibiotics?

• Do I need further surgery?

• What is the likely outcome from this treatment?

• When do I need to come back?