Imaging

Septic Arthritis

Preliminary Diagnosis: Septic Arthritis

I. What imaging technique is first-line for this diagnosis?

  • Plain radiograph.

  • As clinically suspected septic arthritis is a clinical emergency, image-guided joint aspiration is advocated as the first-line imaging technique.

II. Describe the advantages and disadvantages of this technique for diagnosing septic arthritis.

Advantages

  • Quickly and accurately detects moderate to large joint effusions, the first radiographic sign of septic arthritis.

  • Accurately detects sequela of septic arthritis: periarticular osteoporosis, joint space narrowing, and marginal erosions.

  • Provides superior resolution of the osseous structures.

Disadvantages

  • Findings are nonspecific, and joint aspiration is required if septic arthritis is clinically suspected.

  • May not detect small joint effusion.

  • Exposes the patient to a small amount of ionizing radiation.

III. What are the contraindications for the first-line imaging technique?

No significant absolute contraindications exist. Some institutions require consent for pregnant patients.

IV. What alternative imaging techniques are available?

  • Ultrasound

  • MRI with gadolinium.

V. Describe the advantages and disadvantages of the alternative techniques for diagnosing septic arthritis.

Ultrasound

Advantages

  • Highly sensitive for detecting joint effusion, if superficial.

  • Does not require the use of ionizing radiation.

  • May be employed for needle guidance for joint aspiration.

Disadvantages

  • Limited to evaluating joints that are superficial.

  • Findings are nonspecific, and joint aspiration is required if septic arthritis is clinically suspected.

  • Nonspecific for type of joint effusion.

  • Inferior to plain film for osseous detail.

MRI with gadolinium

Advantages

  • Highly sensitive and relatively specific in the appropriate clinical setting.

  • Can accurately identify complications associated with septic arthritis, such as adjacent soft tissue abscess or cellulitis.

  • Does not expose the patient to ionizing radiation.

Disadvantages

  • Findings are often nonspecific and joint aspiration is required if septic arthritis is clinically suspected.

  • Provides less osseous detail compared to plain radiographs.

  • Expensive.

  • Time consuming imaging modality.

  • Requires significant patient cooperation to minimize motion artifact.

VI. What are the contraindications for the alternative imaging techniques?

Ultrasound

No significant contraindications exist.

MRI with gadolinium

  • MR imaging is contraindicated in patients with non-MR compatible metallic hardware or foreign bodies.

  • Gadolinium contrast is contraindicated in patients with a GFR ≤ 30.

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