When your doctor removes your torn ACL, they put a tendon in its place. (Tendons connect muscle to bone.) The goal is to get your knee stable again and give it the full range of motion it had before you got hurt.

When the tendon is put into your knee, it’s known as a graft. Three types of grafts can be used with ACL surgery:

• Autograft. Your doctor uses a tendon from somewhere else in your body (like your other knee, hamstring, or thigh).
• Allograft. This type of graft uses tissue from someone else (a deceased donor).
• Synthetic graft. This is when artificial materials replace the tendon. Silver fibers and silk were among the first ones used (in the early part of the 20th century). More advanced options are available now, like carbon fiber and Teflon, but researchers are still working to find the best material for ACL replacement.