US appearance of avascular necrosis (AVN)

[Linh]

Hi Steve,

One of my colleague noticed bony irregularity at the femoral neck when doing a preliminary imaging before a steroid injection into the hip joint. The radiologist decided to offer a CT to further investigate before putting the needle in and discovered patient has avascular necrosis of the entire weight bearing aspect of his femoral head. Patient has a high pain threshold and is a stoic figure.

In your experience, what is the main signs for suspicion of AVN? What are the differentials on US? Is US reliable?

Best regards,
Linh

[Stephen Bird]

Hi Linh,

That is a wonderful pick,

I have never diagnosed it with ultrasound before.

At the practice I work at we always perform a plain radiograph before we do any MSK ultrasound or injection. If they have had one in the last 6 months we are happy with that. If the referral doesn’t ask for one we do a self determined X-ray.

The reason we do this is highlighted by your example.

Plain radiographs are required to support MSK ultrasound in virtually all cases, otherwise you will often miss changes of arthritis, neoplasms, AVN etc.

To do MSK ultrasound without having a plain radiograph to review is a dangerous practice.

There are occasions when I may not have an X-ray available and I am always very careful to assess the bony surfaces. If something looks funny I will chat to my radiologist and ensure a radiograph is performed before proceeding.

Ultrasound certainly should not be the primary modality to make this diagnosis.

Steve

[Linh]

Thanks Steve. It should be a standard practice to have X-ray performed indeed.

[Stephen Bird]

Yes,

For all MSK ultrasound examinations I think we run the risk of missing significant pathology like ANV events, bone masses, mets etc as well as other joint and bone related variations and pathology if we don’t have a recent plain radiograph series available.

It is cheap and good medicine.

Steve.

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