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Patients ask me how ACL tears are repaired within about thirty seconds of hearing the words “torn ACL.” The short answer surprises most of them. A torn ACL is almost never sewn back together. It is rebuilt.
ACL reconstruction surgery replaces the damaged ligament with a tendon graft, and that graft becomes the new ACL. My own practice is hip and knee replacement, so ACL surgery is handled by my sports medicine partners at the Bone and Joint Institute of Tennessee. What I bring is the long view: after more than twenty years and 700 joint replacements a year, I see what these knees look like at forty, fifty, and sixty.
How Are ACL Tears Repaired?
ACL tears are repaired with ACL reconstruction surgery: the torn ligament is removed and replaced with a tendon graft, threaded through small tunnels drilled in the femur (thigh bone) and tibia (shin bone). The graft is held with a screw or a small button, and it becomes the new ACL over the next several months.
The word “repair” is misleading. Repair means putting the original tissue back together. Reconstruction means building a new ligament from other tissue.
For the ACL, reconstruction is the standard of care.
The work is done through knee arthroscopy. The surgeon uses two or three incisions the width of a pencil, a small camera called an arthroscope, and tools about the size of a chopstick. One longer incision is needed if the graft comes from the patient’s own body.
Most patients go home the same day.
Why Can a Torn ACL Not Just Be Stitched Back Together?
A torn ACL cannot reliably be stitched because it sits inside the joint, bathed in joint fluid, with a blood supply too poor to knit the ends together. Ligaments outside the joint, like the MCL on the inner side of the knee, heal well on their own. The ACL does not.
Surgeons tried direct stitching for decades and gave it up. Modern studies of ACL repair report failure rates several times higher than reconstruction, with the worst numbers in teenagers.
Newer bridge-enhanced repair methods are being studied and look promising for a small group of patients. They are not the standard yet.
What Happens During ACL Reconstruction Surgery?
ACL reconstruction surgery follows the same basic sequence in nearly every case, whether the patient is a high school soccer player from Franklin or a weekend cyclist from Nashville:
- Anesthesia is given, usually with a nerve block that numbs the knee for a day.
- Small portals are made and the arthroscope is placed inside the joint.
- The surgeon checks the meniscus (the C-shaped cushions in the knee) and the cartilage, and repairs any damage found.
- The graft is harvested, unless donor tissue is being used.
- Tunnels are drilled in the femur and tibia at the exact spots where the original ligament attached.
- The graft is pulled through the tunnels, tensioned, and fixed in place.
- The incisions are closed, and the knee goes into a brace.
Here is the part patients rarely hear: the graft is weakest around six to twelve weeks after surgery, while the body turns it into living ligament. That is why the rehab timeline stays slow even though the knee feels good early.
Which Graft Is Used in ACL Reconstruction Surgery?
Most grafts come from the patient’s own body (an autograft): the patellar tendon below the kneecap, the hamstring tendons behind the thigh, or the quadriceps tendon above it. Donor tissue from a tissue bank (an allograft) is the other option.
Autograft is preferred for young athletes: donor tissue carries a much higher re-tear rate in that group.
Allograft is more often chosen for older patients who want a smaller surgery and are not going back to pivoting sport.
How Long Does ACL Reconstruction Surgery Take?
Most ACL reconstruction surgery takes one to two hours in the operating room. Add anesthesia and recovery on either side, and a patient is at the surgery center about four to six hours.
When Should ACL Reconstruction Surgery Be Done?
Most surgeons schedule ACL reconstruction surgery about 3 to 6 weeks after the injury, once swelling has settled and the knee can straighten fully and bend past 120 degrees. Operating on a hot, stiff knee raises the risk of arthrofibrosis, a heavy scarring response that leaves the knee permanently tight.
Those first weeks are not wasted. Patients use them for prehab: motion work and quad control. Knees that arrive strong recover faster.
Waiting too long has its own cost. Delays past three months raise the risk of new meniscus and cartilage damage, because an unstable knee keeps shifting. Studies also suggest that waiting beyond six months lowers the odds of a strong result.
Does Every ACL Tear Need Surgery?
No. Surgery is a choice, not an automatic next step after a torn ligament. It depends far more on how a person uses the knee than on the MRI report.
Nonsurgical care means guided physical therapy, hamstring and quad strengthening, a hinged brace for some patients, and a real change in activity. Straight-line exercise such as running, cycling, swimming, and lifting is usually possible without an intact ACL.
The ACL protects against the pivot: the plant-and-cut motion in soccer, basketball, and football.
Who Does Well Without ACL Reconstruction Surgery?
Patients who do well without ACL reconstruction surgery are typically older, less involved in cutting sports, and free of meniscus or cartilage injury. In my clinic, that is a real group of people.
The line I watch is instability. Each episode of giving way can tear meniscus tissue and bruise cartilage, and that is the path toward arthritis.
A quiet knee can often be managed without surgery. A knee that keeps buckling deserves a surgical opinion.
What Does Recovery After ACL Reconstruction Surgery Look Like?
Recovery after ACL reconstruction surgery takes about six to nine months for everyday function and 9 to 12 months before a return to cutting and pivoting sport. Physical therapy starts within a few days of surgery, not weeks later.
I go through the full timeline in how long recovery takes after a torn ACL. The usual progression looks like this:
- Week 1: crutches and a brace, with early work on full extension and quadriceps activation.
- Weeks 2 to 6: walking without crutches, restoring bend, controlling swelling.
- Months 3 to 5: straight-line running begins.
- Months 5 to 8: cutting and pivoting drills are introduced.
- Months 9 to 12: return-to-sport testing and clearance for competition.
About 85 percent of patients get back to their previous level of activity. The ones who do best take rehab seriously in months four through eight, when the knee already feels fine and the graft is not ready.
What Are the Risks of ACL Reconstruction Surgery?
Most patients have no complications. The honest list includes pain at the front of the knee in 10 to 20 percent of cases and lasting stiffness in fewer than 5 percent. Infection and blood clots are rare.
Graft failure is the risk patients ask about most. Fewer than 10 percent of people tear the same ligament again.
The number that deserves more attention: up to a third of young athletes tear an ACL in one knee or the other within two years of returning to sport. Returning too early is the most common reason.
What Does an ACL Tear Mean for the Knee Twenty Years Later?
An ACL tear raises the lifetime risk of knee arthritis, and surgery lowers that risk without erasing it. This is where my practice and this topic meet.
Post-traumatic arthritis is arthritis that follows an injury rather than simple wear. Many of the forty-five and fifty-year-olds I see for total knee replacement can name the exact game their knee was hurt in.
That is not a reason to fear the injury. It is a reason to protect the meniscus and cartilage early, because those tissues decide how the knee does over the next thirty years.
It is also why strength work and a healthy weight matter long after the sports chapter ends. When arthritis does arrive, it often affects one side of the knee only, which can make a partial knee replacement the better answer.
Where to Have an ACL Tear Evaluated in Middle Tennessee
Any knee that pops, swells within a few hours, or gives way should be evaluated within a week or two, not months later. A physical examination, including the anterior drawer test, an X-ray to rule out fracture, and usually an MRI answer the question.
The Bone and Joint Institute of Tennessee is at 3000 Edward Curd Lane, Franklin, TN 37067. Our surgeons care for patients from Franklin, Nashville, Brentwood, Columbia, Murfreesboro, Spring Hill, and across Middle Tennessee. My sports medicine colleagues handle ACL reconstruction; I see the knees that have moved on to arthritis, and I am glad to help sort out which conversation a patient needs.
Call (615) 791-2630 or request an appointment online. No referral is required.
References
Watch: How a Torn ACL Is Rebuilt With a Patellar Tendon Graft
This short clip shows what the graft actually is and where it comes from, which is the part most patients find hardest to picture.
- Kunze KN, Pareek A, Nwachukwu BU, et al. Clinical results of primary repair versus reconstruction of the anterior cruciate ligament: a systematic review and meta-analysis. Orthop J Sports Med. 2024;12(6). PubMed
- Hughes JD, Lawton CD, Nawabi DH, Pearle AD, Musahl V. Anterior cruciate ligament repair: the current status. J Bone Joint Surg Am. 2020;102(21):1900-1915. PubMed
- Forsythe B, Lu Y, Agarwalla A, et al. Delaying ACL reconstruction beyond 6 months from injury impacts likelihood for clinically significant outcome improvement. Knee. 2021;33:290-297. PubMed
- Gagliardi AG, Carry PM, Parikh HB, et al. ACL repair with suture ligament augmentation is associated with a high failure rate among adolescent patients. Am J Sports Med. 2019;47(3):560-566. PubMed
- Kew ME, Bodkin S, Diduch DR, et al. Reinjury rates in adolescent patients 2 years following ACL reconstruction. J Pediatr Orthop. 2022;42(2):90-95. PubMed
- Potter HG, Jain SK, Ma Y, Black BR, Fung S, Lyman S. Cartilage injury after acute, isolated anterior cruciate ligament tear. Am J Sports Med. 2012;40(2):276-285. PubMed
This article is for educational purposes only and does not replace professional medical advice. Always consult a qualified healthcare provider about your own diagnosis and treatment. Individual results vary based on personal health circumstances.
