As a patient, you may hear these terms and not know what they mean. Simply stated,
In recent years, Allograft tissue has become more popular for ligament reconstruction. The advantage is primarily "donor site morbidity" or problems inherent in borrowing the tissue.
This in real fact is negligible and problems can be minimized at the donor site easily.
The downside of Allograft is that it is not your own tissue and it is more slowly incorporated. It has poor strength characteristics which do not recover nearly as quickly as autograft. It also has a very low risk of disease transmission from the donor.
Years ago, it was thought that there was little antigenicity (body recognition) of tendon and that allograft or even Xenograft would be acceptable. Although there is some antigenicity, this is likely quite variable. Because the tissue is not matched (like a kidney or heart) to the donor, failure can occur more often than with autograft tissue. In an article in which I was a co-author many years ago as a Fellow: "A comparison of patellar tendon autograft and allograft used for anterior cruciate ligament reconstruction in the goat model"
We found that at 1 year the allograft tissue was only roughly half the strength of the autograft tissue.
Current surgeons use the rationalization that failures of allograft are only slightly greater than those of autograft. This surgeon feels that the only time that allograft should be used is when there are poor autograft options. This can occur with prior autograft failure.
In the case of Anterior Cruciate ligament reconstruction, autograft is superior and the donor site morbidity is minimal when harvested carefully. I feel that allograft should only be considered when there is no other option.
Posterior cruciate reconstruction is a different situation. The only way we can create a graft which is as strong as a native Posterior Cruciate is to combine a patellar tendon autograft and a hamstring autograft. This can be done but of course is more likely to create donor site problems.