Lump on clavicle near sternum

Hi, I had RTA in Dec 2010, since have Ben a unable to move arm from waist out wards to ear in stops around 80 degrees. Have had physio which made little difference and visit a chiropractor weekly which helps for few days but results where off.  2 weeks ago I notice a hard lump on clavicle near sternum, had an X-ray and was told it wasn't bone.  Any ideas what this could be?

thanks