From the Guidelines
Evaluation of a Septic Joint
The evaluation of a septic joint should start with clinical suspicion and joint aspiration for diagnosis, as it is an orthopedic emergency that requires rapid diagnosis and intervention to prevent permanent damage to the joint 1.
Key Diagnostic Criteria
The Kocher criteria are widely applied in the evaluation of the hip joint to distinguish septic arthritis from transient synovitis, and include:
- Fever >101.3 F
- Erythrocyte sedimentation rate of at least 40 mm/hour
- White blood cell (WBC) count of at least 12,000 cells/mm3
- Inability to bear weight on the affected side Satisfying more of these criteria results in a higher likelihood of septic arthritis, with near 100% likelihood in patients who meet all four criteria 1.
Imaging Studies
Radiographs can provide anatomic evaluation and demonstrate findings of chronic osteomyelitis, but are often normal in early septic arthritis 1. MRI with contrast is the modality of choice in the evaluation of osteomyelitis, but may not be necessary for the initial evaluation of septic arthritis 1. Ultrasound (US) and fluoroscopy are favored for joint aspirations, and US and CT for abscess drainage 1.
Laboratory Evaluation
Laboratory evaluation should include routine cultures, Gram stain, and cell count with differential 1. Elevated C-reactive protein >2.0 mg/dL has been described as an accurate predictor of septic arthritis 1.
Management
Typical management of septic arthritis consists of antibiotics, arthrotomy, irrigation, and debridement 1. Prompt diagnosis and intervention are critical to prevent permanent damage to the joint.
From the Research
Evaluation of Septic Arthritis
The evaluation of septic arthritis involves a combination of clinical findings, laboratory tests, and imaging studies.
- Clinical findings that suggest septic arthritis include joint pain, swelling, erythema, warmth, and limited range of motion 2, 3, 4.
- Laboratory tests, such as synovial fluid white blood cell count and percentage of polymorphonuclear cells, can aid in the diagnosis of septic arthritis 2.
- Imaging studies, such as X-rays and MRI, may also be used to support the diagnosis, but the gold standard is diagnostic arthrocentesis 3, 4, 5.
Diagnostic Criteria
The diagnostic criteria for septic arthritis include:
- Joint pain and swelling
- Fever
- Limited range of motion
- Tenderness of the joint
- New joint swelling and effusion
- Synovial fluid white blood cell count and percentage of polymorphonuclear cells 2, 4.
Laboratory Tests
Laboratory tests that can aid in the diagnosis of septic arthritis include:
- Synovial fluid white blood cell count
- Percentage of polymorphonuclear cells
- Gram stain and culture of synovial fluid
- Blood tests, such as complete blood count and blood culture 2, 3, 4.
Imaging Studies
Imaging studies that can be used to support the diagnosis of septic arthritis include:
Differential Diagnosis
It is essential to consider mimics of septic arthritis, such as:
- Abscess
- Avascular necrosis
- Cellulitis
- Crystal-induced arthropathies
- Lyme disease
- Malignancy
- Osteomyelitis
- Reactive arthritis
- Rheumatoid arthritis
- Transient synovitis 3.