What is Septic Arthritis?

Septic arthritis is an infection (usually bacterial) that occurs in the joint cavity. It is the most dangerous form of acute arthritis. The joint cavity is usually a sterile space, with synovial fluid and cellular matter including a few white blood cells.

In septic arthritis, germs infiltrate the joint and damage it, causing severe pain. Bacteria most commonly target your knee, though other joints can be affected by septic arthritis, including your ankle, hip, wrist, elbow and shoulder. Septic arthritis usually affects just one joint, though occasionally it may occur in more than one joint at a time.

Prevalence of septic arthritis

The incidence of septic arthritis has been estimated at 2 to 10 cases per 100,000 in the general population and as high as 30 to 70 cases per 100,000 in patients with rheumatoid arthritis.

How it spreads

  • The most common route of spread is hematogenous
  • Other routes include trauma or inoculation as during steroid injections

Signs and Symptoms

  • Patients with septic arthritis usually present with a single swollen joint with pain on active or passive movement
  • The knee is involved in about 50% of the cases, but wrists, ankles, and hips are also commonly affected
  • Septic arthritis may present as polyarticular arthritis in about 10% to 19% of patients
  • It is more common in patients with prior joint damage as in rheumatoid arthritis, gout, and systemic connective tissue disorders

Apart from the above a few others could include:

  • Fever
  • Shaking chills
  • Severe pain in the affected joint, especially when you move that joint
  • Swelling of the affected joint
  • Warmth in the area of the affected joint


Septic arthritis can begin as an infection elsewhere in your body and travel through your bloodstream to the joint. What may begin as an upper respiratory tract infection or urinary tract infection can spread in your body and cause septic arthritis.

The other relatively unknown causes include

  • puncture wounds
  • surgery
  • drug injections

These could allow bacteria to enter into the patient’s body near the affected joint. In other cases, bacteria may enter your body and circulate in your bloodstream, but not cause an infection anywhere else – just in your affected joint.

Types of bacteria

Numerous strains of bacteria could cause septic arthritis. The most common type involved in septic arthritis is Staphylococcus aureus (staph) – a type of bacteria commonly found on your skin and in your nose.

In the past, septic arthritis was more frequently caused by the bacterium that causes the sexually transmitted disease gonorrhea. But better use of safer-sex practices has led to a decline in gonorrhea and its complications, including septic arthritis. Still, in younger sexually active people, gonorrhea is a more likely cause of septic arthritis.

Other infectious causes of arthritis

Bacteria are just one cause of joint infections. Viruses also can attack joints (viral arthritis), though this condition usually resolves on its own and causes little joint damage


Synovial fluid analysis is of paramount importance in the diagnosis and management of septic arthritis. It should include gram stain, culture, leukocyte count with differential, and crystal examination under polarized microscope