Septic Arthritis

This is a medical emergency as the infection can quickly destroy the joint and cause serious systemic illness. The most common cause of it is Staph aureus, and other causes include Neisseria gonorrhoea (in sexually active teens), Group A strep, and E.coli.

Differentials - Transient Synovitis, JIA, Perthes disease, Slipped upper femoral epiphysis

• Transient synovitis presents very similarly to early SA, but has much milder symptoms

Presentation

• Painful, swollen, hot, red knee

• Resistance to attempted movement of joint

  
  

  • Signs can often be subtle in young children, so always consider this as a differential in a child presenting with joint problems, especially if in pain and refusing to move it

Investigations

• Bloods – WCC, CRP, ESR

• Imaging – Joint US, XR, MRI

• Joint Aspiration and MC&S

N.B. Gram stain is positive in ~50% of cases, so a negative gram stain doesn’t rule out infection.

Management

• Urgent washout of joint IV Abx – Starting with broad-spectrum until sensitivities known