You were charged with this? Or you are facing this?
The only suggestion I have is to change your method of disciplene. At 16 yrs old, (in my opinion) spanking isn't very effective and there are alot of consequences with spanking a child of that age. I would suggest strict grounding and taking away of privaledges.
There isn't much you can do if you are charged/faced with this. Just prove your case of using this as discipline and make sure that you didn't "cross over" into legal abuse when you spanked this teen. Things aren't like they use to be when we were children.
Good luck.