As Dr Aaron mentions, numbness and pain when extending the finger doesn't fit in with a particular diagnosis, but there might be different problems that are happening concurrently.
If you are having pain around a finger in particular, it could be something like a trigger finger or degenerative (wear and tear) change within a joint. Equally, there could be nerve compression of some sort happening at the wrist (such as carpal tunnel) or along the course of the nerve as it exits your neck.
If there is associated tingling and weakness, this could point towards a nerve issue, while stiffness and difficulty with movement could be more related to a joint or tendon issue. Of course things might not be so black and white.
Hope this helps.
