MRSA Joint Infection


A joint infection is an infection of the joint fluid. Joints are bathed in fluid that is encapsulated by a fibrous covering. Joint infections are concerning, because left untreated these infections can destroy a joint in a matter of days.


  • Classic presentation is a red, swollen, warm, and painful joint. The joint is termed irritable, because it hurts to move the joint or to have someone else move it.  
  • The hip and knee joints are more commonly infected, but any joint can be affected. 
  • Fevers are common.
  • Other symptoms may include weakness, body aches and fatigue.


The diagnosis of a joint infection is often challenging, because there are many causes for an irritable joint. The diagnosis is determined clinically via the history and physical with the aid of diagnostic testing.

  • Blood work
    • A blood count (CBC) provides evidence for infection, when the white blood cells are elevated. 
    • Sedimentation rate (ESR) and C-reactive protein (CRP) are two separate tests for inflammation, and are often elevated with an infection. 
    • Note: the above blood tests provide evidence for infection, but do not diagnose infection.
  • Ultrasound
    • Ultrasound can identify excess joint fluid, which may indicate an infection.  
    • Ultrasound provides guidance for needle aspiration of the joint.
  • Needle aspiration: Needle aspiration is the process whereby fluid is removed from the joint. A needle is inserted directly into the joint, sometimes under the guidance of ultrasound. Joint fluid is aspirated, and subsequently sent to the lab for evaluation.
    • Microscopic examination: Bacteria and/or a large number of white blood cells (fight infection) provide preliminary evidence for an infection. 
    • Joint fluid is also sent to the lab for testing. Success enables you to know the exact bacteria causing the infection, and which antibiotics will best treat the infection.