Graft material for bones and ligament come from two sources: from the patient (called an autograft or from a donor (allograft). An autograft of meniscal tissue isn't possible at this time.
Scientists are working on removing a small number of cells and regenerating tissue in a laboratory that could be re-injected into the same patient. This is many years away yet.
Allografts are taken from donors who have died from injuries or acute disease. Most donors have been killed in a car accident or had a stroke.
The tissue is screened carefully for any diseases or infection. Tests can be done to look for hepatitis or HIV/AIDS. Donors must not have received steroids or other potent drugs prior to their death. Healthy donor tissue is frozen and matched to the candidate by size.
Research is underway to make an artificial (synthetic or plastic) meniscus.