Usually the meniscus is taken ('harvested') from a cadaver donor, processed in a tissue bank to make it safe and inserted into living recipient, where it replaces their own meniscus. Nowadays it is often harvested still attached to a piece of donor bone, which is slid into a recess made into the recipient's bone so that only the outer edges need to be sewn into place.
Feel free to download this eBook on Managing Meniscal Injuries which explains which tears can be repaired and which can not. It follows on from another eBook in the series - Knee Meniscus Injury. Managing Meniscal Injuries explains the rehabilitation, meniscal repair, meniscal trimming, scaffolds, transplants, and it touches upon avulsion injuries, although we have another in-depth eBook on that topic.