Avascular Necrosis

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.

• 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.