Septic Arthritis
Even with timely antibacterial treatment, an elderly patient with a septic joint has a 7% to 32% mortality rate. Staphylococcus and Streptococcus are the most commonly cultured pathogens, but consider E. coli, Pseudomonas, and Klebsiella species in patients with diabetes mellitus, malignancy, or other debilitating chronic syndromes; less common agents include tuberculosis and gonococcus. Fever may be present, but a recent study revealed that fewer than 60% of geriatric patients with septic arthritis presented with a febrile illness. Thus, systemic features are not reliable enough to warrant making or excluding the diagnosis of septic arthritis without examination of the synovial fluid. (See Table 5, below.)
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Send synovial fluid for leukocyte count, Gram’s stain, and culture in all suspected cases, and several studies suggest that the diagnostic yield may be improved with direct inoculation of fluid into blood culture vials or isolator tubes. Synovial fluid will also show very low glucose (less than 25% of simultaneous plasma glucose) and very high lactate (greater than 10 mm/l) in the untreated bacterial septic joint.
Treatment of a septic joint includes both appropriate antimicrobial therapy and joint drainage. Three weeks of parenteral antimicrobial therapy directed against the isolated pathogen is usually sufficient once the affected joint has been drained. Surgical drainage is indicated in joints—like the hip—that are difficult to aspirate or monitor. Other indications include pus in the synovial fluid, spread of infection to the soft tissues, or an inadequate clinical response to appropriate antibiotics after five to seven days. Otherwise, daily aspiration is the treatment of choice for an uncomplicated infected joint. Additionally, as is true in any acute monoarthritis, bed rest and optimal joint positioning are required to prevent the occurrence of joint deformation and harmful contractures. TH
Dr. Landis is a rheumatologist and a freelance writer.
Special thanks to Bradley Flansbaum, MD, for his assistance with this article.
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