How long until the plates & screws in elbow to fix monteggia fracture can be removed? need another surgery?

Maybe never: Hardware or instrumentation does not always need to be removed unless it is prominent & then painful. Otherwise, the screw holes that remain are potential sites for re fracture until they heal & there is an increased risk of surgical complications with a second surgery & possible range of motion loss. Discuss with your surgeon your options. You have to be healed plus some time depending age.

Why take them out?: The plates and screws use to fix your fracture rarely need to be removed and can be a difficult procedure. Once the fracture is healed, the hardware is no longer needed. If the hardware causes a problem, it can be removed. I would wait 1- 2 yrs before electively removing the hardware. Activity restrictions are needed after surgery for a limited time.