Carbon dioxide bubbles?

[Simpo Two]

About 9 months ago I fell and landed badly on my left thumb, which made a sharp crack under the impact. An X-ray showed it wasn't fractured, so what was the crack noise?

It wasn't getting 100% better so yesterday I went to a physiotherapist. I told him which part of my thumb was affected and after much pulling and squeezing he told me which part of my thumb was affected.

I asked him about the crack noise. He said that when joints are compressed they give off bubbles of CO2 which then collapse and make the noise. That sounded like bks to me because to get gas out of a liquid you reduce, not increase, the pressure (like propellor cavitation).

Was he talking bks or is there a vestige of truth in it?

[RTB]

That's exactly what they are. The sound you hear is the cavitation as the bubble collapses. Basically by increasing the volume (thereby lowering the relative pressure) within the joint (by stretching the joint) you create a "bubble" as the fluid degases, when the joint returns to it's normal volume the bubble collapses.

http://journals.plos.org/plosone/article?id=10.137...

Edited by RTB on Tuesday 14th March 11:17

[Simpo Two]

Thanks. If the joint had been stretched that might make sense - but I fell on my thumb end on - the joints were under sudden severe compression not tension.

[RTB]

Simpo Two said:

Thanks. If the joint had been stretched that might make sense - but I fell on my thumb end on - the joints were under sudden severe compression not tension.

I guess if you were to impinge the joint with enough force you could have the effect of increasing the pressure in the synovial fluid on one side of the joint (as the joint compressed and displaced to one side - the joints will slide past one another), whilst the pressure on the other side momentarily decreased, allowing a gas bubble to form.

Just a guess though.