Question
My friend was playing tackle football (no pads) and hurt his collar bone after a tackle. Pressing a part of the collarbone that is close to the chest causes a lot of pain. A few days later, he's mentioned pain in his shoulder and his neck. The doctor took an xray and found no broken bones, but he still has a lot of pain. Could it be a muscle tear? And are all the different pains related?

Answer
All of the different pains may very well be related.  He most likely straind the joint between the collarbone and the breastbone.  The impact probably transmitted to the outer joint of the collarbone and the shoulder blade.  All of these are connected by muscles of the chest, upper back and neck.  I would suggest, since he has seen his family physician, that he see a chiropractor.  Most likely it is soft tissue that needs to be addressed, but, if there is misalignment involved, a chiropractor should be able to treat this as well.