is the invasion of the joint space by an infectious agent which produces
Arthritis . The usual etiology is bacterial, but viral, mycobacterial, and fungal arthritis occur occasionally. Bacteria are either carried by the bloodstream from an infectious focus elsewhere, introduced by a
Skin Lesion that penetrates the joint, or by extension from adjacent tissue (e.g. bone or bursae).
For bacterial infection,
In newborns, the most common pathogen is
Group B Streptococci .
In children older than 2 or 3, about 50% are due to
Staphylococcus Aureus .
Haemophilus Influenzae Type B used to be a major cause before the use of the
Vaccine .
In sexually active individuals, a major cause is
Neisseria Gonorrhoeae .
Septic arthritis should be suspected when joint (
Monoarthritis ) is affected and the patient is
Febrile . In ''seeding'' arthritis, several joints can be affected simultaneously; this is especially the case when the infection is caused by
Staphylococcus or
Gonococcus bacteria.
Diagnosis is by aspiration (giving a turbid, non-viscous fluid),
Gram Stain and
Culture of fluid from the joint, as well as tell-tale signs in laboratory testing (such as a highly elevated
Neutrophils (approx. 90%),
ESR or
CRP ).
Therapy is usually with
Intravenous Antibiotic s,
Analgesia and washout/aspiration of the joint to dryness.
Traditionally, the diagnosis of septic arthritis was based on clinical assessment and prompt
Arthrocentesis . However, the clinical picture may be obscured by multiple confounding factors and a paucity of specific findings especially for the deep joints, ie. the hip or shoulder. Imaging can be used to confirm the diagnosis of septic arthritis and more importantly, imaging findings suggestive of septic arthritis can direct the clinician to a diagnosis that may not have been considered.
Plain film findings of septic arthritis include: joint effusion, soft tissue swelling, periarticular osteoporosis, loss of joint space, marginal and central erosions and bone
Ankylosis . CT is more sensitive than plain films for the detection of early bone destruction and effusion.
The role of
MRI in the diagnosis of septic arthritis has been increasing in recent years in an effort to detect this entity earlier. Findings are usually evident within 24 hours following the onset of infection and include: synovial enhancement, perisynovial edema and joint effusion. Signal abnormalities in the bone marrow can indicate a concomitant osteomyelitis. The sensitivity and specificity of MRI for the detection of septic arthritis has been reported to be 100% and 77% respectively.
- Septic arthritis by William Brinkman, M.D., University of Washington Department of Radiology
- Karchevsky M, Schweitzer ME, Morrison WB, Parellada JA. MRI findings of septic arthritis and associated osteomyelitis in adults. AJR 2004; 182:119-122.
- Resnick D. ''Bone and joint imaging''. Philadelphia, PA: WB Saunders Co; 1989; 744-749
- Stoller DW, Tirman P, Bredella MA. ''Diagnostic imaging orthopaedics''. Salt Lake City, UT: Amirsys; 2004; 4-99.
- Edwards MS. "Osteomyelitis and Septic Arthritis"
