Is the patellar tendon used in reconstructing the acl?

It can be: The traditional gold standard acl reconstruction uses a patella tendon along with some bone on both sides. There are alternatives aug as hamstring tendon and donor cadaver grafts that are now used more commonly. There are studies that claim each is better than another.

Yes: The patellar tendon and hamstring tendons are the most common grafts used to reconstruct the acl; it cannot be repaired once torn. Another option is to use an allograft which means a cadaver tissue graft from a deseased person. These are also often patellar tendon or hamstring grafts. The literature is mixed but in general, using your own tissue is more successfull than using an allograft.