For the person asking about ACL reconstruct, I hadn't heard the term allograft so I googled and this is what I found...not sure how accurate it is, but it may help your choice.

 

ACL Reconstruction

Graft choices for ACL surgery

 

Anterior cruciate ligament (ACL) reconstruction can be done with several different graft choices. These include patellar tendon, hamstring tendon, and donor tissue (allograft). Each of these choices has advantages and disadvantages.

ACL reconstruction is not an ACL repair. A repair implies that you can fix something that is broken. If an ACL is completely torn, it will not heal back together, even if the torn ends are sewn together. In actuality, the tendon almost always appears frayed when visualized after an ACL tear. What does work well, is to remove the torn ends of the ACL and replace the ligament with a different structure (a graft). To secure the graft into the position of the normal ACL, tunnels are made in the shin bone (tibia) and thigh bone (femur), and the graft is passed through these tunnels to reconstruct the ligament.

Patellar Tendon
The patellar tendon is the structure on the front of your knee that connects the kneecap (patella) to the shin bone (tibia).

• Advantages: Many surgeons prefer the patellar tendon graft because it closely resembles what needs reconstruction. The length of the patellar tendon is about the same as the ACL, and the bone ends of the graft can be placed in to the bone where the ACL attaches. This allows for "bone to bone" healing, something many surgeons consider to be stronger than any other healing method.
• Disadvantages: When the patellar tendon graft is taken, a segment of bone is removed from the kneecap, and about 1/3 of the tendon is removed. There is a risk of patellar fracture or patellar tendon rupture following this surgery. Also, the most common problem following this surgery is pain on the front of the knee ("anterior knee pain"). In fact, patients sometimes say they have pain when kneeling, even years after the surgery.

Hamstring Tendon
The hamstring muscles are the group of muscles on the back of your thigh. When the hamstring tendons are used in ACL surgery, two of the tendons of these muscles are removed, and "bundled" together to create a new ACL. Over the years, methods of fixing these grafts into place have improved.

• Advantages: The most common problem following ACL surgery using the patellar tendon is pain over the front of the knee. Some of this pain is known to be due to the graft and bone that is removed. This is not a problem when using the hamstring tendon. The incision is also smaller, and the pain both in the immediate post-operative period, and down the road, is thought to be less.
• Disadvantages: The primary problem with these grafts is the fixation of the graft in the bone tunnels. When the patellar tendon is used, the bone ends heal to the bone tunnels ("bone to bone" healing). With the hamstring grafts, a longer period of time is necessary for the graft to become rigid. Therefore, people with hamstring grafts are often protected for a longer period of time while the graft heals into place.

Allograft (Donor Tissue)
Allograft is most commonly used in lower demand patients, or patients who are undergoing revision ACL surgery (when an ACL reconstruction fails). Biomechanical studies show that allograft (donor tissue from a cadaver) is not as strong as a patient's own tissue (autograft). For many patients, however, the strength of the reconstructed ACL using an allograft is sufficient for their demands. Therefore this may be an excellent option for patients not planning to participate in high-demand sports (e.g. soccer, basketball, etc.).

• Advantages: Performing the surgery using allograft allows for decreased operative time, no need to remove other tissue to use for the graft, smaller incisions, and less post-operative pain. Furthermore, if the graft were to fail, revision surgery could be performed using either the patellar tendon or hamstring grafts.
• Disadvantages: Historically, these grafts were of poor quality and carried a significant risk of disease transmission. More recently, techniques of allograft preparation have improved dramatically, and these problems have greatly improved. However, the process of graft preparation (freeze-drying), kills the living cells, and decreases the strength of the tissue. There is also the concern of disease transmission. While sterilization and graft preparation minimizes this risk, it does not eliminate it entirely. The risk of complication from other factors unrelated to allograft tissue is much higher than the risk of disease transmission, but it is still there.

Summary
Many surgeons have a preferred technique for different reasons. The strength of patellar tendon and hamstring grafts is essentially equal. There is no right answer as to which is best, at least not one that has been proven in orthopedic studies. The strength of allograft tissue is less than the other grafts, but the strength of both the patellar tendon and hamstring tendon grafts exceed the strength of a normal ACL. The bottom line is 85% to 95% of patients will have clinically stable knees following ACL reconstructive surgery.