Preliminary Diagnosis: Avascular necrosis

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

MRI

II. Describe the advantages and disadvantages of this technique for diagnosis of avascular necrosis.

Advantages

  • Most sensitive and specific imaging technique for diagnosis of avascular necrosis

  • It is the preferred technique for early and accurate detection.

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  • Noninvasive method

  • Does not use ionizing radiation

Disadvantages

  • Expensive

  • Time-consuming imaging modality

  • Requires marked patient cooperation to limit motion artifact

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

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

IV. What alternative imaging techniques are available?

  • Bone scintigraphy

  • CT scan

  • Plain film (radiography)

V. Describe the advantages and disadvantages of the alternative techniques for diagnosis of avascular necrosis.

Bone scintigraphy
Advantages

  • Sensitive in diagnosing avascular osteonecrosis in early stages. However, it is less sensitive than MRI.

Disadvantages

  • Has less sensitivity, show less spatial resolution than the other methods and cannot grade the severity of the disease

  • Includes exposure to ionizing radiation

CT
Advantages

  • High-resolution images of structural anatomy

  • Notably more accurate than conventional radiography in staging the disease

Disadvantages

  • Requires a large amount of ionizing radiation

Plain film
Advantages

  • There is far less radiation exposure using plain film compared with CT.

  • Plain films can be used in staging of the disease.

Disadvantages

  • Low sensitivity level for diagnosis

  • Plain film is less accurate than CT in grading the disease in all stages and cannot show early stages (not sensitive to stages 0 and I).

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

Bone

  • Bone scintigraphy is contraindicated in pregnant and breastfeeding patients.

  • CT is contraindicated in pregnant patients, especially within the first two trimesters.

  • No significant contraindications exist but must be avoided in pregnant patients.

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