Hello.
Thank you for your query at DoctorSpring.com.

I have gone through your son's MRI images. He seems to have a tear of the supraspinatus tendon which is one of the muscle whose tendon forms the rotator cuff at his shoulder.
Your surgeon is right. This has to be surgically repaired. If it is not repaired, it may lead to its continuous impingement and pain.

Hope this was helpful to you. Feel free to ask queries.

With best wishes.