The replacement ligament or tendon (called a graft) chosen for your surgery has the largest controllable impact on your risk of retearing your ACL.
Every anterior cruciate ligament reconstruction (ACLR) has a risk to retear. Research shows each graft type comes with a different retear risk.
Based on your age, sport and activity level, the differences can be significant. You can calculate yours here.
With autograft, the replacement tendon comes from your knee, hamstring or quadriceps. With allograft, it comes from a cadaver, often the Achilles tendon at the back of the heel.
On average, autograft using a patella tendon (from your knee) has the lowest retear risk. Allografts have three times the retear rate of autografts. The younger you are, the more this matters.
Our recommendation: know your retear risk when discussing graft options with your surgeon.
If your goal is to minimize your risk of a retear, graft choice is your most important decision. Your primary criteria should be retear risk.
Here’s what MOON Knee Group research says about ACLR graft options:
These results come from MOON Knee Group’s long-term study of 3,500 ACLR patients at seven institutions in the US. More than five dozen papers have been published based on this research.
Why should the lowest retear risk be your most important criteria in graft choice?
When comparing graft types using the ACL retear risk calculators, use the absolute difference. That is, subtract the lower retear risk number from the higher retear risk number.
Use the difference between the two numbers to determine your graft choice (see the guide to the right or below on mobile).
Why use the absolute difference? Because percentage difference is misleading:
Calculate your expected failure based on the risk calculators and discuss with your doctor the advantages and disadvantages of each autograft type for you.
When the absolute difference between retear risks is:
Regardless of the type of graft used, you can reduce your risk of a repeat ACL tear by 40 to 60 percent by following MOON Knee evidence-based rehabilitation therapy coupled with a return-to-sport program.
All patients should participate in rehabilitation programs before resuming normal activities or returning to sports. Even after six to nine months of recovery, you may still have neuromuscular deficiencies that require fine-tuning.
Below are brief descriptions of each graft type. (Go here for a description of ACL reconstruction surgery.)
Your surgeon will recommend a graft type for you based on your age, sport, position, goals, available time and commitment to rehabilitation, plus any additional injuries in your knee and leg.
The medical community continues to debate the benefits of different graft types. The conversation is evolving. We describe each graft type with general information about the failure rate from the MOON study and what this might mean for your choice.
Know your failure risk for each graft type by using the graft risk calculators.
This autograft type is often called bone-patella tendon-bone (BTB). The patella tendon connects the kneecap and the tibia (shin). The surgeon will remove 9 to 10 millimeters from the middle third of the tendon, keeping small blocks of bone at each end. The surgeon then inserts and fixes the bone blocks inside the tunnels drilled in the thigh and shinbones for the replacement ligament.
BTB autografts have the lowest retear risk.
In a hamstring autograft, multiple bands are taken from your hamstring tendon along the back of your thigh. These bands are joined and fixed into the tunnels in your femur and tibia to reconstruct your ACL. While in some cases hamstring grafts may have a similar retear risk as patella tendon grafts, on average the retear risk with hamstring grafts is higher.
Using bands from the quadriceps tendon to replace an anterior cruciate ligament is a newer development. The surgical technique is similar to using the hamstring tendon. As ACL reconstruction outcomes using quadriceps tendon are not studied in MOON research, there is currently not enough data to draw any conclusions about this graft type.
An allograft comes from a cadaver, often the Achilles tendon. This means there is no second surgical site on your knee or thigh. Yet many surgeons no longer use allografts in young patients. As noted above and elsewhere, allografts are three times more likely to retear than autografts.
This is significant for those 22 and younger. Every competitive athlete younger than their mid-twenties should elect ACL reconstruction using autograft.
For those in their mid-twenties and older, the absolute gap between the two methods becomes insignificant. And those older than their mid-twenties suffer fewer ACL retears overall (research so far provides no conclusive reason for this).