It happened to me too. I'm talking only about my personal experience. Every doctor is different. I had a visit years ago and I had to take off my clothes, so my arms were exposed, and there were past scars. I was so afraid that the doctor would point them out, but he didn't say anything. I tried to hide my arm so I don't know if he saw them or not.
But you will go to the doctor not for your scars, but for a medical problem. So I think the doctor will focus on the visit. Then, you are not obligated to say anything to him or to make an explanation. You can say it's an issue you had in the past, if you want.
Good luck for the appointment