Do you know the specific Brand and Model of both the Acetabular Cup and liner and the femur stem & ball?
Titanium is often used as the base, but other materials - metals, ceramic and polymer - are in/on some components. A few hip implants have been found to have unintentional adverse consequences like metal ions shedding. These do not necessarily show up on x-rays, and unexplained pain can long after surgery be a sign of a developing problem.
Maybe it's time to get the details and start investigating?
Sue