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ACL injury: what rehabilitation looks like and when it is safe to return to sport
Whether you have surgery or not, rehab is the core of ACL recovery. What trials show about surgery vs. rehab first, return-to-sport timing and testing, and preventing the next injury.
Published · 5 min read Leer en español
The anterior cruciate ligament (ACL) keeps the shin bone from sliding and twisting under the thigh bone. It is often torn during a sudden stop, cut or awkward landing. The American Academy of Orthopaedic Surgeons estimates about 200,000 ACL injuries a year in the United States [1]. Female athletes are at higher risk: in high school sports, girls had about 1.6 times the risk of boys per exposure, and girls’ soccer had the highest risk per season [2].
If you or your child has just torn an ACL, here is what the research says about the road back.
Surgery first, or rehab first?
For young, active adults, two well-known trials tested starting with structured rehabilitation and having surgery later only if the knee stayed unstable.
- In the Swedish KANON trial, people who had rehab with optional later surgery did as well at two years as those who had early reconstruction [3]. At five years there was still no meaningful difference in knee scores, activity level or knee osteoarthritis on X-rays [4].
- In the Dutch COMPARE trial, early surgery scored slightly higher at two years (84.7 vs. 79.4 out of 100), a difference the authors described as not clinically relevant [5].
About half the people in the rehab-first groups eventually chose surgery:
| Trial and follow-up | Rehab-first patients who later had reconstruction |
|---|---|
| KANON, 2 years | 23 of 59 (39%) |
| KANON, 5 years | 30 of 59 (51%) |
| COMPARE, 2 years | 41 of 82 (50%) |
Sources: Frobell et al., 2010 and 2013 [3] [4]; Reijman et al., 2021 [5].
That means rehab first is a reasonable option for some people, and for others surgery is the right call. The orthopedic guideline notes that when surgery is chosen for an isolated ACL tear, early reconstruction is preferred, because the risk of further cartilage and meniscus damage starts to rise within three months [1]. This is a decision to make with an orthopedic surgeon, based on your knee, your sport and your goals. Either way, rehabilitation is the backbone of recovery.
What rehab after ACL surgery involves
The physical therapy guideline for knee ligament injuries recommends [6]:
- Moving early, within the first week after surgery
- Supervised rehab in the clinic plus a home program, with education so you can do it correctly on your own
- Strength training for the thigh muscles, starting within 4 to 6 weeks and continuing 2 to 3 times a week for 6 to 10 months
- Neuromuscular electrical stimulation for 6 to 8 weeks alongside strengthening
- Neuromuscular training: balance, landing and movement-control work
- Hop tests to help decide when you are ready to return to activities, and a questionnaire to check psychological readiness, since fear of reinjury can hold people back [6]
A 2023 international guideline adds that a visit before surgery may help, with possible gains in quadriceps strength, knee motion and time to return, though the certainty of that evidence is low [7]. It also calls exercise “the mainstay” of rehab and says the length of rehab should be based on meeting criteria, not just on time [7].
Not everyone gets back to the same level
A meta-analysis of 69 studies with more than 7,500 people found that after ACL reconstruction [8]:
- Returned to any sport81%
- Returned to pre-injury level65%
- Returned to competitive sport55%
Source: Ardern et al., British Journal of Sports Medicine, 2014 [8].
People who returned to their pre-injury level were more likely to have symmetrical hop test results, to be younger, and to have a positive psychological response to recovery [8].
When is it safe to go back?
Returning too early is one of the biggest risks. In the Delaware-Oslo cohort, 100 athletes in pivoting sports were followed for two years after ACL reconstruction [9]:
- Returned before 9 months39.5%
- Returned after 9 months19.4%
Source: Grindem et al., British Journal of Sports Medicine, 2016 [9]. Bars are scaled to 40%.
The reinjury rate dropped by 51% for each month that return was delayed, up to 9 months after surgery [9]. Strength mattered too: each 1-point improvement in quadriceps strength symmetry was linked to a 3% lower reinjury rate [9].
The study also tested a set of criteria: scoring above 90% on quadriceps strength symmetry, four single-leg hop tests, a knee function questionnaire and the athlete’s own rating of knee function. Only 1 of the 18 athletes who passed was reinjured, compared with 21 of 55 who did not pass [9]. The study was small, so that difference was not statistically significant, but together with the timing finding it supports a simple message: wait at least 9 months, and pass objective tests before going back [9].
This matters because second ACL injuries are common. Across 19 studies, 15% of people had a second ACL injury (to either knee), and among athletes under 25 who returned to sport the rate was 23%, nearly 1 in 4 [10].
Preventing ACL injuries
The good news is that ACL injuries can often be prevented. The physical therapy prevention guideline gives its highest grade of recommendation to exercise-based knee injury prevention programs, such as the FIFA 11+ and similar warm-ups, for athletes 12 to 25 years old in high-risk sports, and especially for young female athletes [11]. It recommends using them with all young athletes, not just those screened as high risk [11].
A review that combined eight meta-analyses found these programs cut ACL injuries by about 50% overall, and non-contact ACL injuries in female athletes by about 67% [12]. After reconstruction, the same kind of neuromuscular training in the late phase of rehab may also help prevent a second injury [11].
The takeaway
- Rehabilitation is the core of ACL recovery, with or without surgery.
- Rehab first with optional later surgery is a reasonable option for some young adults, but about half eventually choose reconstruction.
- After surgery, plan on months of progressive strength and neuromuscular training.
- Waiting at least 9 months and passing strength and hop tests before returning is linked to a much lower reinjury rate.
- Prevention warm-ups can cut ACL injury risk roughly in half.
You can start physical therapy in Utah without a referral. Whether you have just been injured, are preparing for surgery or are working toward your return, we can help you plan each phase.