Hi,

WIth your headaches, it is possible that the C5/6 fusion puts more pressure on the other levels in your neck. Therefore, the upper neck joints might be overworking due to many factors such as posture, activities, sports etc.

Headaches that come from the neck often come from the joints OC1, C1/2 and C2/3. They can give many and varied sympotms.

It is likely that the C5/6 is not really the cause of your problems but other issues not seen on XRays or CT etc.

See a good physio and things should be taken care of.