When two bones in the spine are fused, the action of the joints above and below changes. This can lead to problems in the joints above or below the fused area. It could explain why you are having problems at the level just below the fused segments of C5 and C6. Your doctor may want you to work with a physical therapist to help ease pain, improve the quality of neck motion, and optimize your posture. A program like this usually includes strengthening exercises for the neck and upper back muscles. The goal is to help improve your condition and give you ways to take care of future pain or problems with your neck.
However, if you keep having significant pain or develop progressive arm or hand numbness, your doctor will examine you again and make further recommendations. A second surgery may have a lower chance of success because of the scar tissue from the first surgery. You and your doctor will need to discuss the risks and benefits when deciding whether another surgery should be done.