What is usually done for a displaced meniscus to prevent osteoarthritis forming? I have having a lot of medial side pain doc told me to live with it?

Meniscus padding . Missing the meniscus decreases the cushion on your joints. Although there is no way to replace that cushion at this time you can try to have a lateral or medial heel wedge in your shoes depending on the side removed. Appropriately fitted this could shift the pressure to the side with the intact meniscus when you were walking, running etc. Also appropriate exercises such as quadriceps strengthening is important.