Joint Infection
It is possible for joints to become infected. This may occur by two processes: (1) - infection from direct injury or (2) infection via the bloodstream from another infected site such as a skin lesion. Susceptibility to infection by either process is facilitated by chronic inflammation of joints, such as that in rheumatoid arthritis. Similarly, those who are immunocompromised, such as patients with AIDS, patients on immunosuppressant therapy, patients who abuse alcohol and the elderly, are at increased risk of joint infection. Artificial joints may also become infected, analogous to infection of synthetic heart valves causing endocarditis.
Infectious Organisms
Septic arthritis is most commonly caused by Staphylococcus aureus. Less common organisms which may be implicated are: Streptococci, Neisseria gonorrhoeae and Haemophilus influenzae. The latter is more affiliated with childhood joint infection.
Clinical Presentation
A young, fit individual will present with a joint that has an elevated temperature, is red and appears swollen. The patient is often in immense pain and consequently the surrounding muscles will go into spasm to immobilise the joint. An elderly patient may present with symptoms more insidiously. In approximately 20% of cases, multiple joints will be infected.
Investigations
- Aspiration - a sample of fluid must be obtained from the joint and then sent for culture and Gram-Staining. The fluid may have a turbid or purulent appearance.
- Blood Cultures - A blood sample must be cultured for infective organisms
- Full blood count - this is likely to reveal a leucocytosis
- ESR and CRP - These are markers of inflammation and may also be used to ascertain the subsequent response to antibiotic treatment
- Skin wound swabs - The primary site of infection may be a skin lesion
- Sputum culture - Respiratory tract infections may be the primary infection
- Urinanalysis - Urinary tract infection may be the primary infection
Treatment
Intravenous flucloxacillin at a dose of 1-2grams must be administered immediately and given a 6 hour intervals. Other antibiotics e.g. erythromycin or gentamycin, are also suitable in the case of drug allergy and pathogenic insensitivity. The antibiotics must be given for one to two weeks to prevent extensive joint destruction. Surgical drainage may be required if there is joint destruction or osteomyelitis.
