Hi, thanks for writing to HCM.
It is very unusual to develop pain at the site of implant (plate) 19 years after surgery. But there is a possibility of implant breakage due to fatigue
failure over a period of time which could cause discomfort and pain.
Anyway, it is necessary to get an evaluation done to know the exact cause.
An xray of the local part will show the status of the implant and the underlying bone.
If it is bothering you much, then Implant removal may be needed.
Hope this information is helpful. Good day