Does having a plate and 9 screws in your tibia actually make it stronger? Or does it weaken it?

Probably neither!! After surgery, till the fx has healed, the plate/screws maintain the bones alignment while the bone heals. After the fx has healed and you start strengthening exercises, the muscles get stronger and eventually the bone becomes stronger than when it was broken, but i don't believe it becomes stronger than its normal strength. It does not weaken, unless the pt does not complete her exercises.