Hi, My Son Had Cervical Spine Fusion 12 Months Ago

Hi, my son had cervical spine fusion 12 months ago due to a congenital condition, and was in a neck brace for over 12 months as he developed an infection in his wound 6 weeks after surgery. He hasn't been in the neck brace for about 12 months now, but last night he said he had a lump in the area of his chest where the neck brace used to rest, he noticed it then, when he had the brace off and for physio had to move his head back, it would hurt in that region. So since then he has been exercising a lot, and has started a new job, which is fairly physical. He says the lump hurts on physical movement, or when he presses on it. I'm thinking it's probably a muscular...what do you think?