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Tearing your ACL (anterior cruciate ligament) is the most common knee injury, affecting around 200,000 people in the United States each year.

Your ACL is a ligament located on the front (anterior) side of your knee. It crosses with another ligament (the posterior cruciate ligament, or PCL) to help stabilize your knee and prevent excessive forward movement of the thigh bone (femur) over the tibia (shin bone).

An ACL tear is commonly identified by a loud “popping” noise at the time of injury, followed by pain and excessive swelling around the knee.

It’s usually caused by sports that involve a lot of turning, twisting, pivoting, jumping, or sudden changes in direction, such as basketball, soccer, football, tennis, or gymnastics. This is also a common injury for “weekend warrior” types who enjoy leisure sports like skiing.

Though it was once an injury that could end sports careers, advances in research and sports medicine have allowed many athletes to return to sports, even those with severe tears.

Treatment for ACL tears will depend on the severity and prognosis.

First, visit your healthcare professional for a thorough physical assessment. This may include musculoskeletal tests such as the Lachman test and pivot-shift test as well as an MRI to confirm the diagnosis of an ACL tear.

In the majority of cases, a person will have a complete or near-complete ACL tear. Sometimes, a partial tear can occur.

Surgical repair

If surgery is required, the American Academy of Orthopaedic Surgeons 2022 guidelines recommend ACL reconstruction surgery within 3 months of injury to prevent further cartilage or meniscus damage.

The main types of surgery include:

  • ACL reconstruction with an autograph (most common): This procedure is an ACL reconstruction replacing the torn ACL with another ligament that is usually retrieved from the hamstring tendons or patellar (kneecap) tendon. This is known as an autograph.
  • ACL reconstruction with an allograph (less common): This is the same procedure but involves an allograph, which is a ligament from another party (e.g., human cadaver). Due to poorer recovery rates, it’s often reserved for older, active adults.
  • ACL repair (least common): ACL repair involves reattaching the currently existing ACL. However, this is less common due to higher risks of reinjury and complications.
  • BEAR (bridge-enhanced anterior cruciate ligament restoration) implant: a newer, upcoming approach that was approved by the FDA in 2020 which uses a protein-based implant with the patient’s blood to help restore ACL tears. While there are promising studies on this procedure, it still requires more research.

More research is currently underway for ACL repair, and many factors go into choosing the right approach for your treatment. Be sure to speak with your healthcare professional about your options.

Choosing to forego surgery

In some cases, a person may decide not to get surgery even when it is indicated. A person can usually perform day-to-day activities but will have difficulty returning to high level activity since a full ACL tear will not heal on its own.

If a person is willing to give up on their sporting activity (or similar ones that involve twisting and pivoting), has a partial ACL tear that can heal on its own, or is at an age where surgery may pose a greater risk, then they may choose to forego surgery.

If surgery is not required, such as a minor ACL tear or sprain, it’s recommended to work with a physical therapist to rebuild strength and function and to prevent other knee injuries due to instability of the ACL.

While each person is different, you may heal from a partial ACL tear within 3 months, especially if you undergo physical therapy to rebuild strength and function in your knee.

However, depending on the severity of the injury, you may not ever fully recover and may be at higher risk of reinjury if you do not get surgery.

After surgery, recovery time usually takes a minimum of 9 months. This includes the initial healing phases postsurgery and physical therapy.

It’s very important to wait until your ACL reconstruction has healed completely before returning to sports in order to prevent reinjury.

Generally, it takes at least 9 months to recover after ACL reconstruction surgery.

Weeks 1–2

Immediately after surgery, you’ll likely have a lot of swelling and pain. During this time, it’s important to rest, ice, and avoid any activity that results in pain or discomfort.

In most cases, rehabilitation will start within a few days after surgery once the pain and swelling go down. Your physical therapist may recommend gentle walking, aerobic exercise (e.g., a stationary bike), and gradual reintroduction of strength training exercises.

Physical therapy is crucial — especially at this stage — to prevent scar tissue formation and reduce inflammation. It’s important to work on strengthening the quadriceps muscle and regaining 90 degrees of flexion.

Most people discontinue the use of crutches by 2 weeks after surgery, but this can vary greatly based on the specifics of your individual health and surgical procedure.

Often, the use of pain medication is discontinued around 9 days, driving resumes around 11 days (depending on which leg was affected), and people return to work or school around 7–11 days after surgery.

Weeks 3–6

After around 6 weeks, most people can move around normally but still may not be able to perform activities that require deep flexion of the knee.

During this time, your physical therapist will focus on balance and proprioception exercises. They will also introduce basic strength training exercises that aim to strengthen the quadriceps, hamstrings, and surrounding musculature.

It’s important to work closely with your physical therapist and avoid reintroducing sports or activity too soon as this can increase your risk of reinjury.

Months 2–3

By this time, you may be able to gradually reintroduce certain activities as long as you receive clearance from your physical therapist. It’s important that you have a good range of motion and limited swelling before reintroducing exercise.

Your physical therapist may approve reintroduction to some activities that involve a forward motion (e.g., hiking or biking) but should still avoid any activity that requires quick turning or twisting movements.

You’ll likely continue to focus on strength training in your rehabilitation program. Around 3 months, your therapist may start you on a running program that will begin with short-duration jogging, and gradually work up to longer periods of running.

It’s best to continue working with your physical therapist who will continue to modify your exercise and rehabilitation program based on your progress.

Months 3–9

Your physical therapist may begin to recommend that you gradually reintroduce certain movements such as jumping and lateral movement (e.g., side-to-side shuffles).

They may also start to slowly add in sports-specific activity in a controlled fashion. For example, if you play soccer, then may have you practice light kicking or dribbling.

As months go on, your physical therapist will continue incorporating more movement and activity based on how well your knee is healing.

It’s important to note that most people experience great frustration during these months as they may feel that they’re ready to return to sport. However, returning to sport too early — especially when the graft has yet to fully heal — can result in reinjury.

Timelines may vary

While it usually takes around 9 months to heal postsurgery, some people may be approved to return to their sport earlier. On the other hand, some people may need closer to 12 months before returning to their sport.

Your timeline largely depends on how well your injury is healing, your strength levels, and your movement function, which can all vary between individuals.

Your physical therapist and surgeon can perform various tests to determine if you’re ready to return to your normal activities, such as an isokinetic quadriceps strength test and hop test.

Ultimately, it’s best to listen to your surgeon and physical therapist about returning to activity.

Returning too soon to sports — especially those involving twisting, turning, jumping, or pivoting — can greatly increase your risk of injury since you have not given the new graft enough time to heal.

Most research suggests waiting at least 9 months before returning to sports, as well as ensuring sufficient quadriceps and hamstring strength, lowers your risk of reinjury.

For example, one 2016 study found that waiting 9 months before returning to sports led to a 51% reduced risk of reinjury.

Another review found that passing various function assessment tests prior to reintroduction to sport resulted in lower risk of reinjury.

So, it’s best to get proper clearance from your physical therapist or surgeon before returning to your sport.

Reinjury occurs in around 1 in 5 athletes that received ACL reconstruction surgery.

It can be prevented by strictly following your rehabilitation protocol, not returning before you’re ready, and receiving clearance from your surgeon and PT before resuming activities.

However, there is always the risk of reinjury, especially if you return to sports involving a lot of quick turns, pivoting, and jumping.

Can a partial ACL tear heal without surgery?

A partial ACL tear may be able to heal without surgery, though your movement and function may be limited as a result. You should always discuss your options with a healthcare professional.

What should you do immediately after an ACL tear?

If you hear the classic “popping” sound and experience a lot of pain, you should visit your local hospital for an assessment.

How painful is ACL surgery and recovery?

ACL surgery and recovery can be a painful process. However, the pain usually decreases after about 1 to 2 weeks, depending on how a person progresses in physical therapy. The first weeks of physical therapy are crucial to regaining range of motion and preventing the formation of scar tissue.

How long are you out of sports after ACL surgery?

Most athletes are out of sports for at least 9 months after ACL surgery. Some people may be able to return earlier if cleared by their physical therapist or surgeon.

An ACL tear can be a painful and upsetting injury that usually requires surgery.

If you wish to return to your sport, it’s important that you follow a strict rehabilitation program designed by a physical therapist and wait until you receive clearance, which takes an average of nine months of recovery time.

Returning to sport too early can increase your risk of reinjury and prevent you from returning to your sport. So, it’s important to give yourself time to heal.

Though frustrating, many athletes can successfully return to their sport and make a full recovery.