Thank you for your question. His report suggests that he still has some defects at C5-C6 level that may cause nerve impingement. Therefore, due to nerve irritation in the cervical (neck) spine contact between the edges of the vertebrae can cause neck pain. In few people, this pain may be referred and perceived as occurring in the back of head (as electric sensation)- LHERMITTES SIGN, shoulders, arms or chest, rather than just the neck. It will be best that you consult a neurologist who would like to prescribe Pain killers, steroid and muscle relaxants. Other treatments could be cervical orthosis such as a soft cervical collar/stiffer neck brace to restrict neck movement. In addition, cervical traction may also be suggested by the doctor, if condition is severe. Hope this helps.
You need to get his surgeon to explain that one. There should be no defects at the fusion sites.