Investigations

Imaging:

• radiographs of the infected joints are usually normal at presentation, but should be obtained to check for associated osteomyelitis or concurrent joint disease
  • radiographic change indicates that an infection has been present for more than 2 weeks
• ultrasound and MR imaging may detect effusions and inflammation in joints that are difficult to examine (hip and sacroiliac joints)

The definite investigation for defining the infective organism is aspiration of the pus, often under ultrasound guidance. Immediate Gram staining and culture allows the best antibiotic therapy to be chosen.

Other useful investigations include:

• full blood count - raised white cells
• ESR - raised
• blood cultures - positive in 50%
• Salmonella may be cultured from the faeces of patients with sickle cell anaemia

The full blood count and ESR may be normal in the very old and the very young.

Reference:

• (1) Axford JS. Joint and bone infections Medicine 2006;34 (10):405-412.