Septic Arthritis Involving The Knee

If one of the knee joints suddenly gets hot, red and swollen, the physician must rule out an acute septic arthritis. In about 70% of the cases this is due to a Staphylococus aureus infection. The common pus bug that is contained in boils, pimples, infected wounds etc. can on occasion travel internally to other areas in the body such as a knee joint. When this occurs, it usually happens on one knee only.

The physician will aspirate some of he joint fluid under sterile conditions and send it to the lab. The culture will take a day or two, but the immediate Gram stain will often suggest the cause already as a Gram positive staining will identify the Staph. aureus bug. On the other hand, if the Gram stain shows Gram negative cocci, the diagnosis in all likelihood is Neisseria gonorrhoeae. This is one of the major venereal disease bugs.

This bacterium likes to invade the body and often migrates to one of the knee joints, where an acute septic joint is caused. Finally, with a bad throat infection with a Streptococcus bacterium the Gram staining of joint fluid likely will show ovalshaped Gram positive bacteria lined up in chains of 3 to 5 bacteria, which is typical for this group of bacteria. Although the final diagnosis will eventually be available from the culture report, the physician will treat on clinical grounds as waiting for the results could permanently damage the joint surfaces by these very toxic bacteria.

Antibiotic treatment is done with appropriate antibiotics that are initially usually given intravenously and then orally for a period of time. The associated disease from which the bacteria originated has to also be treated simultaneously (Ref.1,p.1147 and 1156).

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Disclaimer:

This outline is only a teaching aid to patients and should stimulate you to ask the right questions when seeing your doctor. However, the responsibility of treatment stays in the hands of your doctor and you.

References:

1. The Merck Manual, 7th edition, by M. H. Beers et al., Whitehouse Station, N.J., 1999. Chapter 157.

2. ABC of rheumatology, second edition, edited by Michael L. Snaith , M.D., BMJ Books, 1999. Chapter 4.

3. The Merck Manual, 7th edition, by M. H. Beers et al., Whitehouse Station, N.J., 1999. Chapter 270.

4. Wheeless' Textbook of Orthopaedics: http://www.wheelessonline.com/

Last Modified: Jan. 22, 2008