Ban Dong Fy (phonetic) Or Similar- Anybody Heard Of It?

My Thai wife has occasionally problems in her legs. She calles it Ban Dong Fy and claims many Thai people have it. I would like to understand what it might be caused by but have no idea what it is.

So- if it is that common- may be someone else has observed it or knows the answer?

It starts like being brused, the shin turns purple or violet for example above the knee. Then the underlying tissue swells up, gets hard and it feels really really hot. When it disappears it might just come up again close to where it was before. Any suggestions? Cheers and thanks Stefan