Septic Arthritis
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Introduction
Septic arthritis is a limb-threatening condition. While a rare cause of joint pain, clinical suspicion should always exist, given the severity of what it can cause.
Knees are the most common joint involved, followed by hips and shoulders.
The Case of...
a simple case introducing clincial presentation and calling for a differential diagnosis to get students thinking.
Causes and Risk Factors
Septic arthritis is most commonly caused by
- Staphylococcus
- Streptococcus
- H. influenza
- Gonococcus
Pathophysiology
Infection may come from direct innoculation of a joint, or from seeding from the blood.
Signs and Symptoms
The classical triad is fever, pain, and decreased range of motion.
In children, fever, lack of weight bearing, an ESR of >40, and a WBC of >12 virtually guarantees a diagnosis.
- history
- physical exam
History
History of present illness
- pain
- fever
- bites
- trauma
Past medical history
- diabetes
- sexually transmitted infections
- underlying joint disease
- prosthetic joint
- cellulitis
- bacteremia
- recent joint injection
Physical Exam
Vital signs may show evidence of systemic infection:
- fever
- tachycardia
Joint exam may show:
- swelling
- warmth
- erythema
- pain with active and passive ROM
When a joint is infected, it will take the position that will maximize its space, and the patient will reposition at rest:
- knee flexion
- hip flexion, abduction, external rotation
Investigations
- lab investigations
- diagnostic imaging
Lab Investigations
Bloodwork should include:
- CBC
- ESR, CRP
- blood cultures x2
Joint fluid analysis should be done for cells, culture, and crystals
Diagnostic Imaging
MRI or bone scan can reveal evidence of infection.
Differential Diagnosis
The differential diagnosis for joint pain is listed here.
Treatments
Pain control should be offered.
The joint should be drained and immobilized. Surgical debridement may be warranted.
IV antibiotics are critical.
- gram positive: cloxacillin or cefazolin; vancomycin if MRSA is suspected
- gram negative: ciprofloxacin, ceftriaxone
Consequences and Course
Resources and References
Topic Development
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