The short version

For many adults, structured rehab with surgery later only if needed works about as well as early surgery. In one major trial, about half of the rehab-first group never had reconstruction.^[2][3]
Kids and teens with open growth plates are different. Delaying or skipping surgery in that group has been linked with more instability and more meniscus tears.^[4]
Your own tissue (autograft) generally fails less often than donor tissue (allograft) in young, active patients.^[6]
The patellar tendon graft causes more kneeling and front-of-knee pain than hamstring or quadriceps tendon grafts.^[5]
Waiting until at least about 9 months after surgery to return to pivoting sports, and passing strength and hop tests first, is linked with far fewer reinjuries.^[9]

What the ACL does and how it tears

The anterior cruciate ligament (ACL) runs through the middle of the knee, from the back of the thigh bone (femur) to the front of the shin bone (tibia). It stops the shin from sliding forward and helps control twisting.

Most ACL tears happen without contact: a sudden stop, a cut, or an awkward landing. People often feel a pop, the knee swells within hours, and it may feel unstable or "give way" afterward. A torn ACL does not heal back together on its own in most cases, but many people can still build a stable, functional knee with strong muscles.

Other structures are often hurt at the same time, especially the meniscus (the knee's cartilage cushions) and other ligaments. Those extra injuries can change the plan, so ask what your MRI shows beyond the ACL itself.

Do you need surgery?

This is the biggest decision, and the research is more balanced than many people expect.

What the trials found

In the KANON trial, 121 young, active adults with a fresh ACL tear were randomly assigned to rehab plus early reconstruction, or rehab with the option of surgery later if the knee stayed unstable. At two years, knee scores were essentially the same in both groups, and the rehab-first strategy meant far fewer operations.^[1] At five years, 51% of the rehab-first group had gone on to reconstruction, and outcomes were still no different between groups, including arthritis on X-ray.^[2]

A second trial in the Netherlands (COMPARE, 167 patients aged 18 to 65) found that early surgery gave slightly better knee scores at two years, but the authors said the difference was not clearly meaningful to patients. Half of the rehab-first group never needed reconstruction.^[3]

Who tends to lean toward surgery

People who want to return to sports with cutting, pivoting or jumping (soccer, basketball, skiing).
Knees that keep giving way despite good rehab.
Repairable meniscus tears or other ligament injuries alongside the ACL tear.
Children and teens who are still growing (see below).

Rehab first is not "doing nothing." It means months of supervised strength and balance work, with surgery kept on the table. If you go this route, ask your surgeon what would make them recommend reconstruction later.

Kids and teens

Young athletes are a separate case. A meta-analysis of pediatric studies found that children treated without surgery or with delayed surgery reported instability far more often, and had about 12 times the odds of developing a meniscus tear after the injury, compared with early reconstruction.^[4]

Because children still have open growth plates near the knee, surgeons use techniques designed to avoid or limit damage to them. The right technique depends on how much growing your child has left. Ask the surgeon how they will protect the growth plates, and how they will monitor growth afterward.

Young athletes also have the highest risk of a second ACL injury once they return to sport (see Returning to sport).

Choosing a graft

Reconstruction replaces the torn ligament with a tendon graft. The graft can come from your own body (autograft) or from a donor (allograft).

Graft	Where it comes from	What the evidence says
Patellar tendon (bone-tendon-bone)	Middle third of the tendon below your kneecap, with a small bone block at each end	Long track record. Highest rate of front-of-knee and kneeling pain of the three autografts.^[5] In one review of women 25 and under, it failed less often than hamstring grafts, though the evidence was rated low quality.^[7]
Hamstring tendons	One or two tendons from the back of your thigh	Less donor-site pain than patellar tendon.^[5] Often paired with an extra stabilizing procedure in high-risk young athletes (see below).^[8]
Quadriceps tendon	Tendon above your kneecap	Lowest donor-site pain in a network meta-analysis of randomized trials. Complications and revision rates did not differ between the three autografts in that analysis.^[5]
Allograft (donor)	Tendon from a deceased donor	No harvest site, shorter surgery. In young, active patients, failed about 25% of the time versus about 10% for autografts in one review.^[6] Often reserved for older or less active patients, or revision surgery.

There is no single best graft for everyone. Your age, sport, sex, whether you kneel for work, and your surgeon's experience all matter. Ask which graft they use most and why they would pick it for you.

Extra procedures you may hear about

Lateral extra-articular tenodesis (LET). A strip of tissue from the outside of the thigh is used to add rotational control. In the STABILITY trial of 618 high-risk patients aged 25 and under, adding LET to a hamstring reconstruction cut graft ruptures from 11% to 4% over two years. Patients with LET had a bit more pain in the first months, but no meaningful difference later.^[8]

Meniscus repair or trimming. If the meniscus is torn, surgeons may stitch it (repair) or trim the damaged part. Repair usually means a slower, more protected early recovery. Ask which one is planned and how it changes your rehab.

What happens on surgery day

ACL reconstruction is usually done arthroscopically, through small incisions with a camera, and most people go home the same day. You'll typically have general anesthesia, often with a nerve block to help with pain afterward.

The surgeon removes the torn ligament remnant, takes the graft (if using your own tissue), drills small tunnels in the femur and tibia in the positions of the original ligament, passes the graft through, and fixes it in place with screws or buttons. The graft then slowly remodels into a ligament-like tissue over many months.

Many surgeons prefer to operate once swelling has settled and you've regained motion. Ask about "prehab" before surgery: getting your knee straight and your quadriceps working beforehand makes the early recovery easier.

Recovery, month by month

Every surgeon has their own protocol, and protocols change with meniscus repair or other procedures. This is a typical shape, not a schedule to follow on your own.

Weeks 0 to 2Control swelling with ice, compression and elevation. The biggest early goals are getting the knee fully straight and getting the thigh muscle to fire. Crutches, often with a brace.
Weeks 2 to 6Walking without crutches when your team clears you. Stationary bike, bending range improving, more strength work.
Months 2 to 4Building real leg strength. Balance and control work. Many people start a return-to-running program around the end of this window if strength and swelling allow.
Months 4 to 9Running, jumping and agility drills that build toward sport. Strength and hop testing to measure how the operated leg compares to the other side.
9 months and beyondReturn to full pivoting sport for many athletes, only after passing return-to-sport testing.^[9]

Braces and ice

A systematic review of 12 randomized trials found no evidence that wearing a brace after reconstruction improved pain, range of motion, graft stability or protection from reinjury.^[13] Many surgeons still use one early on for comfort or after meniscus repair, so follow your own plan.

Cold therapy is better supported for comfort: a meta-analysis of seven randomized trials found it lowered pain after ACL reconstruction, though it didn't change range of motion or swelling drainage.^[14]

Returning to sport, and the risk of another tear

This is where the numbers get serious. In a meta-analysis of studies on second ACL injuries, about 15% of patients overall tore an ACL again (in the reconstructed knee or the other one). For athletes under 25 who returned to sport, it was about 23%, close to one in four.^[10]

Timing and testing matter. In the Delaware-Oslo cohort of athletes in pivoting sports, the reinjury rate dropped by 51% for each month return to sport was delayed, up to 9 months after surgery. Of those who failed the return-to-sport tests, 38% were reinjured, versus about 6% of those who passed.^[9]

Getting back to sport at all is not guaranteed. Across 69 studies of more than 7,500 people, 81% returned to some sport after reconstruction, 65% got back to their pre-injury level, and 55% returned to competitive sport.^[11]

Injury prevention programs

Warm-up programs that train landing, cutting and balance (often called neuromuscular training) are among the best-proven tools in sports medicine. A summary of eight meta-analyses found they cut ACL injuries by about half across athletes, and non-contact ACL injuries in female athletes by about two-thirds.^[12] Ask your physical therapist to build one into your long-term routine.

Ask your surgeon and physical therapist which tests you'll need to pass before going back, not just how many months it has been.

Risks and complications

ACL reconstruction is a common operation, and serious complications are uncommon, but you should know the main ones:

Stiffness, especially trouble getting the knee fully straight.
Graft failure or a new tear in either knee, most often in young athletes (see above).
Pain at the graft site, including kneeling pain with patellar tendon grafts.^[5]
Infection and blood clots, which are rare but need quick treatment.
Arthritis later in life. Knees with ACL injuries have a higher risk of arthritis over time. In the KANON trial, early surgery did not reduce arthritis on X-ray at five years compared with rehab first.^[2] A review of 41 long-term studies found arthritis rates more than 10 years after injury varied enormously between studies, and having meniscus tissue removed was the only consistent risk factor.^[15] That's one reason surgeons try to repair a torn meniscus when they can.

Questions to ask your surgeon

Based on my knee and my goals, would rehab first be reasonable for me? What would make you recommend surgery later?
What does my MRI show besides the ACL, and does that change the timing?
Which graft do you recommend for me, and why? Which do you use most?
Would you add a lateral tenodesis (LET) in my case?
If my meniscus is torn, do you plan to repair it or trim it, and how does that change recovery?
Which tests will I need to pass before returning to sport?
Who will run my physical therapy, and how often will I go?
For a child: how will you protect the growth plates, and how will you monitor growth afterward?

Recovery supplies

We're putting together vetted picks at a range of prices. Until then, these are the categories most people end up needing:

Ice packs or a cold therapy unit
Compression sleeve
Crutches (if not supplied)
Shower chair or stool
Leg elevation pillow
Resistance bands
Stationary bike access
Loose shorts for a brace

Check with your surgeon before buying a brace or cold therapy unit. Many practices supply one, and the evidence for braces after reconstruction is weak.^[13]

Sources

Frobell RB, et al. A randomized trial of treatment for acute anterior cruciate ligament tears. N Engl J Med. 2010;363:331-42. https://doi.org/10.1056/NEJMoa0907797
Frobell RB, et al. Treatment for acute anterior cruciate ligament tear: five year outcome of randomised trial. BMJ. 2013;346:f232. https://doi.org/10.1136/bmj.f232
Reijman M, et al. Early surgical reconstruction versus rehabilitation with elective delayed reconstruction for patients with anterior cruciate ligament rupture: COMPARE randomised controlled trial. BMJ. 2021;372:n375. https://doi.org/10.1136/bmj.n375
Dunn KL, et al. Early operative versus delayed or nonoperative treatment of anterior cruciate ligament injuries in pediatric patients (summary of Ramski DE, et al. Am J Sports Med. 2014). J Athl Train. 2016;51:425-7. https://doi.org/10.4085/1062-6050.51.5.11
Kunze KN, et al. Lower donor site morbidity with hamstring and quadriceps tendon autograft compared with bone-patellar tendon-bone autograft after ACL reconstruction: network meta-analysis of randomized controlled trials. Knee Surg Sports Traumatol Arthrosc. 2023;31:3339-52. https://doi.org/10.1007/s00167-023-07402-2
Wasserstein D, et al. A systematic review of failed anterior cruciate ligament reconstruction with autograft compared with allograft in young patients. Sports Health. 2015;7:207-16. https://doi.org/10.1177/1941738115579030
Etzel CM, et al. Graft choice for anterior cruciate ligament reconstruction in women aged 25 years and younger: a systematic review. Sports Health. 2022;14:829-41. https://doi.org/10.1177/19417381221079632
Getgood AMJ, et al. Lateral extra-articular tenodesis reduces failure of hamstring tendon autograft ACL reconstruction: 2-year outcomes from the STABILITY study randomized clinical trial. Am J Sports Med. 2020;48:285-97. https://doi.org/10.1177/0363546519896333
Grindem H, et al. Simple decision rules can reduce reinjury risk by 84% after ACL reconstruction: the Delaware-Oslo ACL cohort study. Br J Sports Med. 2016;50:804-8. https://doi.org/10.1136/bjsports-2016-096031
Wiggins AJ, et al. Risk of secondary injury in younger athletes after anterior cruciate ligament reconstruction: a systematic review and meta-analysis. Am J Sports Med. 2016;44:1861-76. https://doi.org/10.1177/0363546515621554
Ardern CL, et al. Fifty-five per cent return to competitive sport following anterior cruciate ligament reconstruction surgery: an updated systematic review and meta-analysis. Br J Sports Med. 2014;48:1543-52. https://doi.org/10.1136/bjsports-2013-093398
Webster KE, Hewett TE. Meta-analysis of meta-analyses of anterior cruciate ligament injury reduction training programs. J Orthop Res. 2018;36:2696-708. https://doi.org/10.1002/jor.24043
Wright RW, Fetzer GB. Bracing after ACL reconstruction: a systematic review. Clin Orthop Relat Res. 2007;455:162-8. https://doi.org/10.1097/BLO.0b013e31802c9360
Raynor MC, et al. Cryotherapy after ACL reconstruction: a meta-analysis. J Knee Surg. 2005;18:123-9. https://doi.org/10.1055/s-0030-1248169
Lie MM, et al. What's the rate of knee osteoarthritis 10 years after anterior cruciate ligament injury? An updated systematic review. Br J Sports Med. 2019;53:1162-7. https://doi.org/10.1136/bjsports-2018-099751

Spot an error? Tell us and we'll check it and fix it.

ACL reconstruction, explained