Most operations don't come with a 100 per cent guarantee. There are too many factors that can affect the final outcome. Sometimes patients don't follow the rehab program carefully. Stiffness, loss of motion, and loss of function are the final outcomes.
In other cases, factors out of the patient's control can affect the results. For example, an infection can cause implant loosening and failure.
Revision surgery may be more helpful for some problems than for others. When soft tissue tightness called contracture prevents motion, then implant revision may work well.
If there's a problem with the implant size, design, or other structural problems, then gains in motion and function following revision surgery may only be modest.