2 evenings ago I got up from my desk barefoot and immediately had a knot form with associated pain on the bottom ball of my left foot under the little toe. Started bruising also. The next day the bruising got worse but the knot seemed to go away. Went to doc and she ordered an xray and it did not show a fracture. Right after xray the knot got bigger and the bruising is now from the ball of my foot over half way down my foot on the outside portion. Bruising color is black to purple. Doc wants to do a mri but has no idea what is causing this. I am a triathlete but again this happened after i had been sitting most of the day working.
Since bone is very vascular, injury to a bone can cause significant bruising. Athletes who compete in repetitive activity such as running are at risk for developing stress reactions (all the way to a stress fracture).
However, frank fractures usually show up on x-ray, especially ones which would cause that much bruising. To have that much blood in the subcutaneous tissues, you have had to have damaged something.
Since you are an elite athlete, who probably wants to continue, figuring out what is going on is the first step. So, the MRI is probably warranted.
If you are not seeing an orthopedic surgeon, you probably should be. If possible, you may want to see an orthopedic foot and ankle surgeon.