Imaging

Knee Effusion

Preliminary Diagnosis: Knee effusion

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

Ultrasound (gray scale and color Doppler imaging)

II. Describe the advantages and disadvantages of this technique for diagnosis of knee effusion.

Advantages

  • Diagnostic

  • Safe, cost-effective

  • Fast and ready available

  • Intraarticular fluid can be easily detected

  • Can also evaluate for other associated findings, such as synovitis or the presence of a Baker's cyst

Disadvantages

  • Less accurate in obese patients

  • May miss small effusions

  • Operator dependent

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

  • There are no contraindications for ultrasound.

IV. What alternative imaging techniques are available?

  • Plain radiographs

  • MRI

V. Describe the advantages and disadvantages of the alternative techniques for diagnosis of knee effusion.

Plain radiographs

Advantages

  • Readily available, fast, low-cost imaging technique

  • Are also useful for osteoarticular evaluation

Disadvantages

  • Exposure to ionizing radiation

  • Limited for soft tissue evaluation, offers poor anatomic detail

  • Findings are often indirect signs and not specific

MRI

Advantages

  • Diagnostic for knee effusions

  • May be able to detect the underlying cause of the effusion and other internal derangements of the knee joint

  • Does not include exposure to ionizing radiation

Disadvantages

  • Expensive

  • Time-consuming

  • Requires significant patient cooperation to minimize motion artifact

  • May be uncomfortable for claustrophobic and obese patients

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

Plain radiographs

  • Contraindicated in pregnant women, especially within the first and second trimesters

MRI

  • Patients with non-MRI compatible implanted electronic devices or implants

  • MR imaging also relatively contraindicated in pregnant women within the first trimester due to the lack of studies regarding the effect of the magnetic field on the embryo

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