Patellar Tendon Autograft for ACL Reconstruction

September 29, 2026

A patellar tendon autograft is a strip of tissue harvested from your own kneecap region and used to replace a torn anterior cruciate ligament. Surgeons take the middle third of the patellar tendon along with small bone plugs from the kneecap and shinbone, creating what is often called a bone-patellar tendon-bone (BPTB) graft. It has been a go-to choice for ACL reconstruction in young, active patients for decades, prized for its bone-to-bone healing and low failure rates, though it comes with a well-documented tradeoff in the form of pain at the harvest site.

What Gets Harvested and How It Is Fixed in Place

The graft itself is a rectangular strip of tendon, roughly 9 to 10 millimeters wide, flanked on each end by a small block of bone. One bone plug comes from the lower pole of the patella, the other from the tibial tubercle just below. These bone plugs are the graft’s distinguishing feature: when placed inside drilled tunnels in the femur and tibia, bone heals to bone rather than soft tissue trying to bond with the tunnel wall. That distinction matters for how quickly the graft anchors itself and how much it resists slipping under load.

The bone plugs are typically secured with interference screws threaded alongside them in the tunnels. A classic concern was whether smaller endoscopic screws would hold as well as the larger screws used in older open techniques, but biomechanical testing found no meaningful difference in fixation strength between 7-mm endoscopic screws and 9-mm rear-entry screws when properly placed.¹ Screw placement on the cortical versus cancellous side of the bone plug also does not significantly change initial fixation strength, though it does influence how failure occurs if the construct is loaded to breaking point.²

One comparison that often comes up is how interference screw fixation performs with BPTB grafts versus hamstring tendon grafts. When both are fixed with interference screws, the patellar tendon construct is substantially stronger at time zero: one study measured roughly twice the failure load and twice the stiffness for BPTB fixation compared to hamstring fixation using screws designed specifically for soft tissue.³ That initial mechanical advantage is one reason the BPTB graft has historically been favored for athletes who want to load the knee aggressively early in rehab.

Newer Fixation Alternatives

Interference screws remain the standard, but cortical suspensory devices — small buttons or loops that anchor on the outer surface of the bone rather than inside the tunnel — have gained interest as an alternative for the femoral side. A Scandinavian registry study comparing a fixed-loop cortical device to a metal interference screw for femoral fixation found no significant difference in revision rates at two or five years, and no meaningful difference in patient-reported knee quality of life.⁴

The tradeoff is mechanical behavior under cyclic loading. Bench testing consistently shows that suspensory devices allow more micromotion during repeated loading cycles — roughly 2 to 3 mm of cyclic displacement compared with about 1.3 to 1.7 mm for interference screws — and lower overall construct stiffness.⁵ Ultimate load to failure, though, is similar between the two.⁶ Whether that extra micromotion translates to clinical problems remains an open question; registry data so far suggest it does not.

How the Graft Heals Inside the Knee

After surgery, the transplanted tendon goes through a transformation called ligamentization: it gradually remodels to resemble a ligament rather than a tendon. The process was first described in the mid-1980s when researchers observed that patellar tendon placed in the anatomic position of the ACL eventually took on ligament-like characteristics, initially surviving on synovial fluid nutrients before new blood vessels grew in after about six weeks.⁷

The bone plug side of things heals faster. New bone begins anchoring the plug within about three weeks, though the bone cells inside the plug itself remain dead for roughly 12 weeks before being replaced by living bone.⁸ The tendon portion takes much longer. Tissue retrieved from patients who needed early revision surgery showed immature collagen and active remodeling months after the original operation, while tissue from later revisions looked more like normal ligament with mature fibers extending fully into the tunnel wall.⁹

A sheep study that tracked the process out to a full year found the graft’s mechanical strength recovered to only about half that of a normal ligament at 52 weeks.¹⁰ That timeline explains why surgeons and therapists take return-to-sport criteria seriously even when the knee feels stable: the graft is still remodeling well beyond the point where symptoms resolve.

How Strong Is the Graft Compared to Your Original ACL

One reason surgeons trust the BPTB graft is that its initial strength exceeds what the native ACL provides. Biomechanical modeling found that a 7-mm patellar tendon graft was about 11% stronger than the intact ACL under simulated loading.¹¹ Of course, that strength refers to the graft on the day of implantation. During the necrosis and revascularization phases of healing, mechanical properties temporarily drop, which is the weakest window for the reconstruction. Strength gradually rebuilds through the collagen remodeling stages described above.

The Donor Site Problem

The biggest downside of the patellar tendon autograft is what it does to the front of the knee where the graft was taken. After the central third of the tendon is removed, the remaining tissue has to heal across a gap, and the surgical incision crosses an area dense with nerve fibers. That creates two distinct problems: anterior knee pain and numbness.

The reported incidence of anterior knee pain varies enormously across studies, from as low as about 5% to nearly 50%, depending on how pain is defined and when patients are assessed.¹² The pain is most pronounced early on. One large cohort study found that about a quarter of BPTB patients reported anterior knee pain at six months compared with only 6% of hamstring graft patients, but by one and two years the difference was no longer statistically significant.¹³ At five years, BPTB patients were still somewhat more likely to report pain, but it was mostly mild and did not affect activity scores, sports participation, or quality of life.

Kneeling is a different story. Difficulty kneeling tends to persist longer and is more clearly linked to graft choice. Data from the New Zealand ACL Registry found that at two years, about 21% of BPTB patients reported significant kneeling difficulty compared with roughly 9% of hamstring patients.¹⁴ For people whose jobs or hobbies involve a lot of kneeling — flooring installers, gardeners, religious practitioners who kneel regularly — that is a practical consideration worth discussing with a surgeon before choosing a graft type.

Numbness around the incision site is also common. A prospective study tracking patient-reported numbness found that about 70% of all ACL reconstruction patients reported some numbness at six weeks regardless of graft type. BPTB patients reported higher severity early on, but numbness tended to fade over the first year for all groups.¹⁵ Surgical technique matters here: a subcutaneous two-incision harvest technique has been shown to cause substantially less sensory disturbance than the traditional single-incision approach.¹⁶

Does the Harvest Damage the Kneecap

A reasonable worry is that cutting into the patella to take a bone plug might weaken it enough to cause a fracture. The risk is real but small. Recent biomechanical testing compared patellae with 20-mm and 25-mm bone plug harvests and found no significant difference in ultimate load to failure between the two, even though the longer harvest removed close to half the patella’s length.¹⁷ Both groups withstood loads well above what the kneecap would experience during normal activity.

Another concern is that closing the tendon defect after harvest might pull the kneecap lower, a condition called patella baja that can limit knee motion. Studies measuring patellar height before and after surgery have found negligible changes. One study reported an average shortening of the tendon of roughly 1 mm after defect closure, and no patients developed patella baja.¹⁸ A separate study using the Insall-Salvati index found no significant differences in patellar height before and after surgery.¹⁹

Patellar Tendon Versus Hamstring Tendon

The rivalry between patellar tendon and hamstring tendon autografts has been debated for decades. On graft survival, patellar tendon has a consistent edge. A meta-analysis pooling over 47,000 patients found that BPTB grafts ruptured at a rate of about 2.8%, nearly identical to the hamstring group’s 2.8%, but the adjusted odds still slightly favored BPTB.²⁰ An earlier meta-analysis had found a more dramatic difference, with patellar tendon graft failure at about 2% versus nearly 5% for hamstrings.²¹ A French multicenter cohort with over 24 months of follow-up reported an even starker gap: 2.1% failure for patellar tendon versus 6.5% for hamstrings, with hamstring grafts failing earlier on average.²²

Knee laxity tests, which measure how well the reconstruction restores normal joint tightness, generally show similar outcomes between the two graft types. In that large meta-analysis, there was no statistically significant difference on the pivot-shift test, Lachman test, or instrumented laxity measurements.²³ The practical difference between the grafts comes down to where you prefer to take the hit: front-of-knee pain and kneeling problems with patellar tendon, or hamstring weakness and potentially higher re-tear rates with hamstring.

The Quadriceps Tendon as an Emerging Alternative

The quadriceps tendon, harvested from just above the kneecap, has become a popular third option. A systematic review and meta-analysis comparing quadriceps tendon to BPTB autografts found no significant differences in knee laxity measurements, pivot-shift grades, Lysholm scores, subjective knee function scores, or graft failure rates.²⁴ The one area where quadriceps tendon clearly won was donor-site pain, with substantially less harvest-site discomfort. A more recent systematic review found mixed results on functional outcomes: some studies showed equivalent performance, while one found BPTB patients scored as “normal” on the International Knee Documentation Committee scale more often than quadriceps patients.²⁵

The trade-off profile is still being refined. Some evidence suggests quadriceps grafts carry lower donor-site morbidity but potentially a slightly higher risk of graft rupture compared with BPTB grafts.²⁶ The research base for quadriceps tendon is smaller and younger than for BPTB, so long-term data are still catching up.

Return to Sport

Getting back on the field is often the question patients care about most. A study of rugby players who received patellar tendon autografts found an overall return-to-play rate of about 85%, with three-quarters returning to the same competitive level at a mean of roughly 11 months. Among professionals, the rate was even higher: 93% returned, at a mean of about 10 months.²⁷

Across a broader population, the picture is more sobering. A long-term follow-up of pivoting-sport athletes found that while 83% returned to some form of pivoting sport after ACL reconstruction, only 53% made it back to their preinjury level.²⁸ In a matched comparison of young athletes, about 57% of those who received BPTB grafts returned to preinjury activity levels, compared with 44% of those with hamstring grafts, though the difference was not statistically significant.²⁹ Psychological readiness, fear of re-injury, and life circumstances probably account for more of the gap between surgical success and actual return to preinjury levels than any graft-specific limitation.

Rehabilitation After a Patellar Tendon Autograft

Rehabilitation protocols for BPTB reconstruction have shifted dramatically over the past few decades. Early programs kept patients non-weight-bearing for weeks and limited knee motion, but accelerated protocols that emphasize early weight-bearing and full extension have largely replaced them. A systematic review comparing delayed and accelerated weight-bearing found that accelerated patients sometimes had better quadriceps strength at three months, though the advantage usually evened out by six months.³⁰

An important question is whether pushing the graft early stretches it out. A study that tracked patients on an accelerated program for two to six years found no evidence of graft stretching: KT-1000 arthrometer measurements (a standard test of knee laxity) were essentially identical at the time of full range-of-motion return and at final follow-up years later, and 97% reported no instability episodes.³¹ That finding has been influential in giving therapists and surgeons confidence that early loading does not compromise the reconstruction.

Adolescents and Open Growth Plates

Using a patellar tendon autograft in teenagers raises a specific worry: the drill tunnels for ACL reconstruction cross through the growth plates of the femur and tibia, and a graft anchored with bone plugs sitting inside those tunnels could theoretically tether growth. A study of adolescents in Tanner stages 3 and 4 — meaning puberty was underway but growth plates were still clearly open — found no growth plate disturbances, no gross leg deformities, and no significant leg-length differences after transphyseal BPTB reconstruction. Boys grew an average of nearly 12 cm and girls about 7 cm after surgery without incident.³² That said, the concern about growth disturbance remains a reason many pediatric sports surgeons prefer physeal-sparing techniques for younger or less skeletally mature patients.³³

Long-Term Joint Health

Perhaps the most sobering data on patellar tendon autograft reconstruction come from long-term follow-up studies tracking arthritis. At a median of 25 years after surgery, about 60% of patients had radiographic osteoarthritis in their reconstructed knee compared with 18% in the opposite knee.³⁴ Another long-term study found grade II or worse degenerative changes in roughly three-quarters of patients, with a fifth showing grade III or IV changes.³⁵

These numbers can be alarming, but context matters. ACL tears themselves, regardless of treatment, accelerate arthritis. Cartilage damage and meniscal tears sustained at the time of injury are among the strongest predictors of later joint degeneration, and many patients already have some cartilage injury before they reach the operating room. Whether the graft type itself changes the long-term arthritis trajectory, or whether the original injury is the primary driver, is still not fully settled.

Platelet-Rich Plasma at the Harvest Site

One attempt to address donor-site morbidity involves applying platelet-rich plasma (PRP) to the tendon defect at the time of surgery. A randomized controlled trial found that patients who received PRP at the harvest site had a significantly smaller tendon gap on imaging compared with controls.³⁶ Another trial reported that PRP-treated patients scored higher on a patellar tendon function scale, and a somewhat larger proportion showed satisfactory bone gap filling, though the bone-healing difference did not reach statistical significance.³⁷ PRP has not become standard practice for BPTB harvest sites, partly because the clinical benefits in pain and function have been modest and inconsistent, but the concept of biologically augmenting donor-site healing remains an active area of research.