Pain: Why is hardware painful?

Pain from Fixation Hardware

Tenderness
Hardware is well named. The screws and plates are hard and can be felt as tender points under the skin. This type of pain is easy to understand and diagnose.
Diffuse Pain
Even if not tender hardware can cause a diffuse aching pain. The reasons are not well understood but may be due to the small electrical currents which are set up when a metal object is placed in a salt solution. Some people's pain fibers are sensitive enough to be stimulated by this current and feel pain as a result.

- makes me wonder if it was worth it: to get the hardware!