SGEM#39: Weak in the Knees (Diagnosis of Septic Joint)

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Date: June 2, 2013
Title: Weak in the Knees (Diagnosis of Septic Joint)

Guest Host: Dr. Chris Carpenter

Case Scenario: 40yo construction worker presents to the emergency department with a swollen and painful right knee. No history of injury. No significant past medical history. Palpable effusion on examination with no overlying redness or warmth to touch. Any movement of the joint is very painful. He is taking no medications. Vital signs are normal.

Question: What history, physical or diagnositc studies can help in the diagnosis of septic arthritis?

Background: There are many causes for monoarticular arthropothies which present to the emergency department. These include trauma, rheumatoid, lupus and infectious (viral, fungal, and bacterial). Septic arthritis due to bacteria has an incidence rate of 10 per 100,000 each year in the USA. The incidence is higher in patients with prosthetic joints or pre-existing rheumatoid arthritis. Immunocompromised patients with HIV are also at increase risk of septic arthritis.

Septic Monoarticular Arthropothies:

Knees (50%)
Hips, shoulders and elbows
Any joint can ultimately be infected

Prompt diagnosis and appropriate treatment is required to prevent morbidity and mortality. Previous research has suggested that most cases of acute monoarticular arthropoties can be diagnosed using history, physical examination and diagnostic testing in three days. However, most emergency physicians only have a few hours not three days to differentiate between septic and non-septic arthritis.

Reference: Carpenter CR et al. Evidence-based Diagnositcs: Adult Septic Arthritis. Academic Emergency Medicine 2011

Population: Adult patients
Intervention: History and physical examination and laboratory testing (serum and synovial)
Control: Unaided clinical gestalt
Outcome: Diagnostic accuracy (sensitivity, specificity and likely hood ratios)

Results: Prevalence of non-gonococal septic arthritis in the ED patients

EBM Extras:

MOOSE Criteria: Meta-analysis of Observational Studies in Epidemiology (MOOSE) statement is intended for the reporting of meta-analyses of observational studies.
QUADAS: Quality Assessment of Diagnostic Accuracy Studies (QUADAS). This is an evidence based quality assessment tool to be used in systematic reviews of diagnostic accuracy studies.
STARD Criteria: Standards for Reporting Studies of Diagnostic Accuracy (STARD). The objective of the STARD initiative is to improve the accuracy and completeness of reporting of studies of diagnostic accuracy, to allow readers to assess the potential for bias in the study (internal validity) and to evaluate its generalisability (external validity).

Authors Conclusions: “Recent joint surgery or cellulitis overlying a prosthetic hip or knee were the only findings on history or physical examination that significantly alter the probability of nongonococcal septic arthritis. Extreme values of sWBC (>50 · 109 ⁄ L) can increase, but not decrease, the probability of septic arthritis. Future ED-based diagnostic trials are needed to evaluate the role of clinical gestalt and the efficacy of nontraditional synovial markers such as lactate.”

BEEM Comments:

Limited search to English
Low to moderate QUADAS scores
Excluded gonococcal infections
Lacked definitive septic arthritis treatment randomized controlled trials
No patient-centred outcomes reported

BEEM Bottom Line: When it comes to the accuracy of history, physical examination, serum tests or synovial tests for the diagnosis of septic arthritis in ED patients we just don’t know but synovial lactate looks promising.

Case Resolution: You successfully tap the knee and send the synovial fluid off for examination. Orthopaedics is consulted. Three days later you get the lab tests back describing urate crystals consistent with gout.

KEENER KONTEST: Last week’s winner was Dr. Chris Edwards from Australia. I challenged TheSGEM listeners to come up with some ED themed memes. A meme is “an idea, behavior, or style that spreads from person to person within a culture.” A meme acts as a unit for carrying cultural ideas, symbols, or practices that can be transmitted from one mind to another through writing, speech, gestures, rituals, or other imitable phenomena. Supporters of the concept regard memes as cultural analogues to genes in that they self-replicate, mutate, and respond to selective pressures.

Be sure to listen to this weeks podcast for another chance to a cool skeptical prize. Email your answer to TheSGEM@gmail.com. Use “Keener Kontest” in the subject line. First one to email me the correct answer wins.

Remember to be skeptical of anything you learn, even if you heard it on The Skeptics Guide to Emergency Medicine. Talk with you next week.