Free body in 4th PIP joint

[Xue Heng]

Hi, Steve.
Here is a similar case.
The 39-year-old male patient is asymptomatic at the 4th PIP joint.
He had no previous history of trauma.
A free body was observed in the 4th PIP joint, beneath the volar plate.
What might be the cause of the free body and is there any clinical significance?
Thank you very much.

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[Stephen Bird]

Tricky one Xue,

I don’t think it is a loose body.

I have never seen a loose body that is linear and conforms to the shape pf the pharyngeal neck like this appearance,

My favourite option is that it is a bit of nitrogen gas that has come out of solution due to negative pressure in the joint. This is common.

Another option would be a slurry of some sort of crystal deposition but I think this is less likely.

I don’t think it is a significant finding and if it is gas as I suspect it is normal.

You could scan it again and see if it is still there or disappeared.

Steve

[Stephen Bird]

Thinking about this one more, I think another piece of evidence that it is most likely gas, but possibly some crystal deposition and not a loose body is not only the linear shape and the way it conforms to the shape of the phalyngeal neck, but also the fact that there is no acoustic shadow from it. If it was an orthopaedic loose body it should shadow densely.

Gas is still my preferred differential diagnosis.

Steve

[Xue Heng]

Hi, Steve.
Is gas possible?
I think for typical gas, there should be ringdown artifact deep to the echogenic surface.
It was not loose body either, because there was no dense shadow, as you say.
The patient was asymptomatic, so there was no follow up.

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