If anterior cruciate ligament (ACL) reconstruction is recommended, an important decision is what tissue should be used to make the new ligament. The main choices are part of your own patellar tendon, quadriceps tendon or hamstring tendon—known as autografts—or donated human tissue, known as an allograft.
There is no single “best” ACL graft for every patient. Age, sport, occupation, previous surgery and personal priorities all matter. Graft choice is only one part of knee reconstruction. Accurate surgery, rehabilitation and a safe return-to-sport plan remain essential.
How strong are ACL grafts?
A young adult’s native ACL can withstand roughly 1,700–2,160 newtons (N) in laboratory testing. Reported starting strengths are approximately 2,900 N for patellar tendon, 2,350 N for quadriceps tendon and 4,000 N or more for four-strand hamstring. Figures vary with graft thickness and testing methods (biomechanics review).
This does not mean a hamstring graft makes the knee twice as strong as the original ACL. After surgery, blood vessels and cells grow into the graft as it becomes more ligament-like—a process called ligamentisation. Fixation and healing, not starting strength alone, protect it during recovery.
Patellar tendon graft
This uses the middle of the patellar tendon below the kneecap, with bone at each end. The bone ends often heal within their tunnels over approximately six to eight weeks, while the graft matures for many months.
Patellar grafts have long-term evidence and low re-rupture rates, making them a common option for young pivoting-sport athletes. Disadvantages include a longer front scar and more anterior or kneeling pain. A review found anterior knee pain rates of 5.4%–48.4% and kneeling pain of 4.0%–75.6%; wide ranges reflect varied methods and definitions (systematic review).
Temporary thigh weakness can occur. Rare complications include patellar fracture or tendon injury. This option may be less attractive for frequent kneelers.
Quadriceps tendon graft
The quadriceps tendon above the kneecap provides a thick graft, with or without a small bone block. It usually leaves a short scar.
Quadriceps grafts tend to cause less kneeling pain than patellar grafts and preserve the hamstrings. Their main disadvantage is early weakness in the front thigh muscles, relevant to jumping, landing and slowing.
A tendon-only graft takes roughly eight to twelve weeks to attach within bone tunnels, but maturation continues for at least 12 months. Evidence indicates quadriceps, hamstring and patellar autografts provide similar stability, patient-reported results and survival (2026 meta-analysis).
Hamstring tendon graft
A hamstring graft folds one or two inner-thigh tendons into several strands. It has high starting strength, small incisions and usually less kneeling pain than a patellar graft.
Disadvantages include weakness when bending the knee, particularly deeply, and variable graft thickness. Hamstrings matter for sprinting and controlling the shin bone. Soft-tissue attachment within bone tunnels usually takes longer than bone-to-bone healing.
Graft diameter and sporting demands need particular attention in smaller adolescents and young pivoting-sport athletes. Evidence has not established patellar or hamstring graft as better for every adult, although patellar grafts cause more anterior and kneeling pain (Cochrane review).
Allograft
An allograft is donated tissue. With no tendon harvested from the patient, there is less early pain, weakness and scarring. It can be useful in revision or multi-ligament surgery, or for selected older, less active patients.
The important drawback is slower biological incorporation. Although the knee may feel more comfortable early because there is no graft-harvest site, the allograft itself does not heal faster. Reviews describe slower revascularisation and incorporation than with autograft tissue (review of allograft healing). Tissue processing also matters: high-dose irradiation used during sterilisation may weaken a graft.
Allograft failure is a particular concern in young, active patients. The MOON prospective study found that the odds of graft rupture were about four times higher with allograft than autograft after accounting for age (MOON cohort study). A review of patients aged 19 or younger reported pooled failure rates of 25.5% for allograft, 8.5% for patellar tendon autograft and 16.6% for hamstring autograft (systematic review and meta-analysis). These group averages cannot predict exactly what will happen to one patient.
Return to sport and patient satisfaction
ACL reconstruction does not guarantee a return to the same sport or level. Across different grafts, a large analysis found that 81% of patients returned to some sport, 65% returned to their pre-injury level and 55% returned to competitive sport (British Journal of Sports Medicine meta-analysis).
Research has not shown that one autograft consistently produces better satisfaction or return-to-sport results for every patient. Confidence, strength, movement control, associated meniscus or cartilage injuries and fear of another injury can be as important as graft choice. Younger age, high exposure to pivoting sport and returning before adequate recovery all increase re-injury risk.
Return-to-sport decisions should therefore consider time since surgery, swelling, movement, strength, hopping ability, confidence and sport-specific skills. Feeling good at a few months does not mean the graft has finished maturing.
Which graft suits which patient?
For teenagers and young competitive athletes in pivoting sports, an autograft is generally preferred because allograft failure rates are higher. Patellar or quadriceps tendon may be considered when reducing re-rupture risk is a high priority, balanced against possible pain or weakness at the harvest site.
Hamstring grafts can suit many active patients, particularly those who kneel frequently or wish to avoid a larger scar at the front of the knee. The possible effect on hamstring strength should be discussed. For an older recreational patient, autograft remains appropriate, but a carefully selected allograft may sometimes be reasonable if avoiding tendon harvest is important. Revision surgery requires a personalised plan based on the previous graft, existing bone tunnels and other causes of instability. Children with open growth plates need specialised techniques.
The best ACL reconstruction graft is the one most appropriately matched to the individual patient. The final choice should be made through a balanced discussion of the evidence, your knee, your activities and your priorities.
This article provides general information only and should not be considered individual medical advice. Treatment decisions should be made following a thorough assessment and discussion with your treating orthopaedic surgeon. It is not possible to determine the most appropriate procedure without considering your individual symptoms, examination findings and imaging.
