Removal of an intramuscular lipoma. How do I go about finding a doctor that knows about them?

I had a ultrasound that showed a solid mass tumor. I then went for an MRI and it shows what appears to be an intramuscular Lipoma 4x3x10cm in my Deltoid muscle. My family dr said nothing to worry about and it needed no treatment. That conflicts with everything I am finding on them. Second opinion today and this dr also does not know anything about them and at my insistence referred me to an orthopedic surgeon. How do I go about finding a Dr that knows about them? Range of motion is effected.