ACL Repair & Reconstruction
Treatment Information
The ACL is a crucial ligament located in the center of your knee, providing essential rotational stability during activities that involve cutting, twisting, and pivoting.
If you think you may have torn your ACL, get evaluated quickly.
Reparative treatment (BEAR) is time-sensitive. The window to repair your own ACL, versus using a graft, closes within roughly the first 50 days after injury.
Even if BEAR isn't right for you, an early evaluation lets us protect any meniscus or cartilage damage and start prehab.
ACL Treatment Videos
Dr. Nathe has performed over 1,400 ACL reconstruction surgeries and is experienced in all techniques, including BEAR ACL Repair.
Dr. Nathe takes pride in matching the right ACL treatment to the right patient. He’ll evaluate your injury alongside the bigger picture – your activity level, overall health, knee history, and desired outcomes – to help you determine which treatment plan is right for you.
What is the ACL?
The anterior cruciate ligament, known as the ACL, is one of four major ligaments holding your knee together. It runs through the center of the joint, from the back of your femur to the front of your tibia, crossing the posterior cruciate ligament in an X. It’s about the size of your pinky finger and made of thousands of densely packed collagen fibers.
The ACL has two jobs. It prevents your shin bone from sliding forward on your thigh bone, and it provides rotational stability. When you plant your foot and cut, pivot, or change direction, the ACL keeps your knee from buckling inward. It’s the reason you can run sideways, pivot on a basketball court, or carve a turn skiing.
When the ACL tears, the knee loses that rotational stability. You can usually still walk, and often still run in straight lines. But anything that requires your knee to resist rotation can make it can give out.
How do ACL tears happen?
About 70% of ACL tears are non-contact. You don’t need to be hit. A typical scenario: you’re running, you plant your foot to change direction, your knee rotates in a way the ACL can’t tolerate, and you feel (and often hear) a pop. Your knee buckles.
Another classic mechanism is skiing. Typically the downhill ski edge gets loaded and the skier begins to crash. As their backseat falls below their ski, the ACL tears when the binding doesnt detach. In my experience, a crash, pop, and toboggan ride down the mountain ends up being an ACL tear about 95% of the time.
Women tear ACLs at 2–8× the rate of men in comparable sports. The reasons are a mix of anatomy, hormonal influence on ligament laxity, and — importantly — modifiable neuromuscular patterns. Well-designed prevention programs, like the FIFA 11+, can meaningfully lower that risk.
Classic mechanisms for ACL tears:
- Cutting and pivoting – soccer, basketball, football, lacrosse
- Landing from a jump – volleyball, basketball, gymnastics
- Deceleration – sudden stop while running
- Ski injury – the ski catches, the body rotates, the knee doesn’t
- Direct blow – a tackle or collision forcing the knee inward
What you typically feel:
- A pop – often audible, almost always felt
- Immediate sensation that something inside the knee is wrong
- Inability to continue playing
- Swelling within 2-4 hours from bleeding inside the joint
- A feeling of instability when you try to plant and turn
Diagnosing Your ACL Injury
Physical Exam:
A careful exam can often diagnose an ACL tear before any imaging. The most reliable tests are the Lachman and the pivot shift — the single most specific test for ACL injury. A skilled examiner is right about the diagnosis before the MRI roughly 95% of the time.
MRI:
MRI is the gold standard. It confirms the ACL tear, tells us whether it’s complete or partial, and shows us everything else. Roughly half of ACL tears occur alongside a meniscus tear, and a meaningful minority have damage to other ligaments or cartilage surfaces. The MRI also shows the tear pattern, which determines whether you’re a candidate for BEAR repair (proximal tears) or whether reconstruction is the right path.
X-Rays:
X-rays don’t show ligaments, but I get them to rule out fracture, look at alignment, and occasionally identify an “avulsion fracture” where the ACL has pulled off a small piece of bone.
If you were recently injured, timing matters.
If you’re within the first several weeks of your injury, you may be a candidate for BEAR repair. This is a newer technique that repairs your own ACL rather than replacing it with a graft, but the window is time-sensitive. Dr. Nathe will evaluate your MRI and your situation to let you know whether this option is on the table.
Learn more about BEAR ACL Repair →
Is surgery the right choice?
Not always. If your knee feels stable and your goals are activities like cycling, walking, or light jogging, many patients do very well with a structured rehabilitation program, particularly when there’s no meniscus damage involved.
When Dr. Nathe recommends surgery:
- You want to return to cutting, pivoting, or jumping sports (soccer, basketball, football, lacrosse, tennis, skiing, competitive volleyball)
- Your knee feels unstable in daily life — it gives way walking on uneven ground, going down stairs, turning in the kitchen
- You have a repairable meniscus tear — an unstable knee can’t protect a meniscus repair, and losing meniscal tissue is a major long-term predictor of arthritis
- You’re young, active, and want to keep your cartilage intact for the next several decades
When nonoperative treatment is reasonable:
- You are an older or less active patient whose sports are largely straight-line (running, cycling, swimming, hiking)
- Your knee is stable in daily life after the initial swelling resolves and you’ve rebuilt quad strength
- There’s no associated meniscus tear that requires surgical attention
- You’re willing to accept some modification of your activities
Many individuals return successfully to cycling, walking, and light jogging after completing a comprehensive rehabilitation program – even with an ACL-deficient knee.
But if your goal is to return to pivoting, jumping, or skiing, surgery is generally recommended to restore the rotational stability the ACL provides.
Reconstruction vs. Repair
There are two surgical routes we can take to address your torn ACL: reconstructive surgery or reparative surgery with a BEAR implant. Both can get you back to the activities you care about. Which one is right for you depends on your injury pattern, your timeline, and your goals.
Read on to learn more about your reconstruction and repair options, or download the handout below.
What are my ACL Reconstruction Options?
There are several options to choose from for a graft to replace your ACL. The ACL is reconstructed with a tendon, and over time your body grows blood vessels into that tendon and remodels the tendon into a new ligament. This process is called “ligamentization” and takes approximately 9-12 months.
The first decision is whether to use a tendon from a cadaver (allograft) or from yourself (autograft). The biggest difference is the rate of re-tear after surgery. For young people, there is a higher risk of re-tear with allograft tissue, and autograft is recommended. For people over the age of 45, the difference becomes less substantial and allograft becomes a reasonable option.
Autograft vs. Allograft
Autografts:
If you decide to use an autograft, there are three options: Patellar, Hamstring, and Quadriceps Tendons.
The Gold Standard
Patellar Tendon (BTB)
The middle third of the patellar tendon, harvested with a piece of bone from the kneecap and a piece from the tibia (bone-tendon-bone). The best option for young athletes with closed growth plates.
Advantages:
- Strong graft
- Excellent bone-to-bone fixation
- Lowest risk of failure of any option in young athletes
- Lowest risk of failure and need for revision
Disadvantages:
- Risk of kneeling pain and small patch of numb skin to the outside of the incision
- Risk of patellar tendinitis pain that is rare
- Very rare chance of patellar tendon rupture or patella fracture
- The hardest to rehab of all the options
High-Risk Athletes
Quadriceps Tendon
A strip of the quadriceps tendon, harvested from just above the kneecap. A great graft for high-risk athletes, and particularly useful when patellar tendon isn’t an option (open growth plates, prior BTB harvest in revision settings).
Advantages:
- Strong graft
- Potentially less anterior knee pain compared to the patellar tendon
- Low risk of failure and need for revision
Disadvantages:
- May have a slightly higher risk of complications such as tendonitis or weakness in knee extension
- On average 5-10% quadriceps weakness long term
- This option is newer, and we do not fully understand the long-term risks later in life
Great for 30+
Hamstring Tendon
Two of the hamstring tendons (semitendinosus ± gracilis), harvested through a 2.5–3 cm incision on the front of the shin. A great option for recreational athletes age 30 and above.
Advantages:
- Smaller scar
- Less postoperative pain
- Easier recovery in the first few months
- Lowest risk of donor site morbidity (pain and weakness) of the autograft options
- Equal risk of retear to other autograft options in patients age 30 and above.
- Easiest rehab of the autograft options.
Disadvantages:
- Higher retear rate than patellar tendon autograft in ages 15-25 (approximately 12% vs. 5% according to the MOON study)
- On average 20% hamstring weakness long term
- Rare chronic hamstring pulls
Great for 45+
Allografts:
Advantages:
- No donor site pain and weakness
- Easier early rehab and recovery
Disadvantages:
- Higher re-tear rate in younger patients – generally not a good option under age 40
- Very remote chance of disease transmission
Lateral Extra-Articular Tenodesis (LET)
In some cases, Dr. Nathe will recommend adding a LET to ACL reconstruction. LET reinforces the outside of the knee with a portion of the iliotibial band. In patients under 25 having reconstruction with hamstring autograft, LET has been shown to reduce re-tear rates from 11% down to 4%. Dr. Nathe typically recommends LET when there is very young age, significant baseline knee hyperextension, high-risk pivot sport participation, or a strong family history of ACL injury.
Image via Miach Orthopaedics, BEAR Implant
What is BEAR ACL Repair?
BEAR (Bridge Enhanced ACL Repair) is a newer technique that involves repairing your existing ACL rather than replacing it with a graft. A special implant is used to help the torn ligament heal back together.
Advantages:
- Preserves your natural knee anatomy and function. Your own ACL stays in place.
- Lower long-term arthritis risk compared with reconstruction.
- Faster return of muscle strength — no donor tendon harvested means no quad, hamstring, or patellar tendon to recover from.
- Better proprioception. Your native ACL contains nerve fibers that contribute to the knee’s sense of position. BEAR preserves them.
- Higher patient satisfaction in early studies.
- No donor site morbidity — no kneeling pain, no patellar tendon scar, no hamstring weakness.
Disadvantages:
- BEAR is a newer technique – we don’t yet have 20 years of data like we do with reconstruction. Long-term durability data is still being collected.
- It is currently best suited specifically for proximal tears
- BEAR has a re-tear rate that is roughly equivalent to hamstring autograft reconstruction. While that’s excellent, for the highest-demand athletes I generally still recommend reconstruction with a higher-strength autograft.
The Procedure
ACL surgery is performed as an outpatient procedure under general anesthesia plus a regional nerve block. You go home the same day.
What happens in the operating room:
- Arthroscopy. I begin by looking inside the knee through two small (1/4-inch) incisions with a camera. I confirm the tear and address everything else — meniscus tears get repaired whenever possible, and cartilage injuries are addressed.
- For BEAR: the implant is placed at the site of the torn ACL, and the torn ends of your own ligament are sutured to the implant, which then helps the ligament heal back together.
- For reconstruction: I prepare the graft, drill anatomic tunnels through the tibia and femur at the original ACL attachment points, pass the graft through both tunnels, and secure it under appropriate tension. Tunnel position is the single most important technical factor in ACL reconstruction.
- If LET is part of the plan, I take a strip of iliotibial band from a small additional incision on the outside of the thigh and secure it to reinforce the lateral side of the knee.
- Closure. Small incisions are closed with absorbable sutures and covered with clean dressings. Total OR time typically 60–75 minutes.
Rehab Timeline
ACL surgery is roughly 30% operation, 70% rehabilitation. A technically perfect surgery followed by poor rehab produces a mediocre result. A solid surgery with disciplined rehab produces an excellent one.
Day 0
Surgery Day
Home the same day
You’ll go home in a brace, on crutches, with ice and medications. The regional nerve block reduces pain for the first 12-24 hours.
Week 1
Protection
Control swelling, regain extension
The single most important goal of Week 1 is getting the knee fully straight. Straight beats everything else this week. Formal PT starts 4–7 days after surgery. Most ACLR patients are off crutches at 2 weeks; BEAR patients stay at ~50% weight-bearing for 4 weeks to protect the repair.
Week 2-6
Range of Motion
Formal physical therapy continues
Goal: 0–120° of motion by 6 weeks. Stationary bike (no resistance, seated) starts around week 3. Brace comes off around 2 weeks for ACLR (longer for BEAR or with meniscus repair).
Months 2-4
Strength
Rebuild the muscles that protect your knee
Core, hips, quads, hamstrings, and calves. The quad atrophies dramatically after ACL surgery and needs the most focused attention. Closed-chain strengthening, single-leg work, and progressive loading drive this phase.
Months 4-6
Neuromuscular
Re-teach the knee to cut
Plyometrics, agility, change-of-direction work, sport-specific drills. Progress is based on objective strength and functional testing, not just time on the calendar.
Months 7-12
Return to sport
Testing, not timelines
Return to cutting/pivoting sports is based on passing a return-to-sport test battery, not a date on the calendar. The graft is still maturing – ligamentization takes 9–12 months. Dr. Nathe typically clears patients no earlier than 9 months from surgery. Returning too early is the single biggest predictor of re-tear.
My Physical Therapy Protocols:
Frequently Asked Questions
Can an ACL heal on its own?
In the large majority of cases, no. The ACL lives inside the joint, bathed in joint fluid that interferes with clot formation and traditional healing. The BEAR implant works by providing a scaffold that allows healing to take place in that hostile environment — that’s the innovation that makes BEAR possible. A complete ACL tear without intervention generally does not heal on its own.
How soon should I be evaluated?
Sooner is better, especially if BEAR repair is something you’d like to consider. The window for BEAR is roughly the first 50 days after injury. Even if BEAR isn’t the right fit, an early evaluation lets us protect any meniscus or cartilage injury and start a structured prehab program – which improves outcomes regardless of which surgery you ultimately have.
How long after injury should I have surgery?
The knee needs to recover from the acute injury first — swelling down, motion close to full, the quad firing. Operating on an acutely swollen, stiff knee leads to worse outcomes. Most reconstruction patients have surgery 2–6 weeks after injury. BEAR has a tighter window (roughly the first 50 days). Meniscus repairs occasionally drive a faster timeline.
How is BEAR repair different from ACL reconstruction?
Reconstruction replaces your torn ACL with a tendon graft. BEAR repairs your existing ACL using a collagen implant that helps the ligament heal back together. BEAR preserves your native anatomy, including the nerve fibers in your own ACL. It’s only an option for certain tear patterns (proximal tears), in patients seen early after injury, and is currently best suited for lower-risk patients given that the published re-tear rate is noninferior (equivalent) to hamstring reconstruction.
Which graft has the lowest re-tear rate?
In young competitive athletes, the best current data supports patellar tendon (BTB) and quadriceps tendon autograft. Hamstring carries a higher re-tear rate than BTB in ages 15–25 (12% vs. 5% per MOON). Allograft has higher re-tear rates in young patients and is generally not my first choice for that population. After age 30, the autograft choices have roughly equivalent re-tear rates.
Will I need a brace to play sports?
The evidence that functional ACL braces reduce re-tear rates is weak. Some patients feel more confident with one for the first season back; most do not need one long-term.
How many ACL surgeries have you done?
Over 1,400 to date, across the full range of techniques (BEAR, BTB, quadriceps, hamstring, allograft, with and without LET). I don’t believe in a one-graft-for-everyone approach; the right answer depends on your knee and your goals.
What about PRP or stem cells for ACL tears?
Interesting early research, but nothing that changes the fundamental picture: a complete ACL tear in an athlete who wants to return to cutting sports is still a surgical problem. The biological augmentation story for ACL is genuinely interesting (BEAR is one example of where biology has finally caught up), but PRP or stem cells alone don’t replace the need for repair or reconstruction.
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