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Knee Injury (ACL) Health Decision Guide

You have some decisions to make about how to best treat your injury. One treatment choice isn't right for everyone. Your decision will be based on the specific nature of your injury, how it's affecting your lifestyle and the types of activities you participate in.

Think of yourself and your doctor as partners in the decision about how to treat your injury. You'll want to carefully consider your options and their trade-offs in relation to your lifestyle and what's important to you. The information presented here is intended to help you decide which treatment is best for you.

You can watch and listen directly to people who have made different choices as well as from a sports medicine doctor at Mayo Clinic. We also offer some key questions to help you in this important decision-making process.

It takes about 30 minutes or more to go through this information in sequence by following the links at left or at the end of each page. This helps you understand more about anterior cruciate ligament (ACL) injuries, your treatment options, why other people made the choices they did and the trade-offs to consider in making your decision.


About an ACL injury

Injuries to the ACL are among the most common of all sports-related knee injuries. It's estimated that each year in the United States between 95,000 and 250,000 people sustain a torn or ruptured ACL.

An ACL becomes torn when it's stretched beyond its normal range of elasticity. Generally the injury is related to a sports or fitness activity, although a torn ACL doesn't usually result from contact between players. Once the ligament tears, it doesn't heal it remains loose.

Women have ACL injuries more often than men do. The exact reason for this isn't clear. It may be due to differences in anatomy, hormones, strength or conditioning.


What is an ACL?

Your knee contains four ligaments that connect the thighbone (femur) to the shinbone (tibia). These ligaments hold the bones in proper alignment and help control the way your knee moves.

The two ligaments on either side of the knee are called collateral ligaments. They provide side-to-side stability. The other two ligaments are inside the knee and cross each other as they stretch diagonally from the bottom of the thighbone to the top of the shinbone. The posterior cruciate ligament (PCL) connects to the back of the shinbone, and the ACL connects near the front of the shinbone. Both provide front-to-back stability.

The ACL controls the movement of your lower leg bone in several ways. It limits the side-to-side rotation of your lower leg and prevents the tibia from moving too far forward in relation to the knee. It also keeps your knee from extending beyond its normal range of motion.


How does an ACL injury occur?

Most ACL tears occur during sports and fitness activities, such as football, basketball, soccer and skiing. Typically they happen when you slow down suddenly or cut or pivot with your foot firmly planted, twisting or overextending the knee. This type of stress in the knee can stretch the ACL beyond its limit and tear it. Landing awkwardly from a jump is also a frequent cause of ACL injury. This type of injury usually doesn't result from contact with other players.

When you tear your ACL, you may feel or hear a pop in the knee, feel significant pain in the knee and have immediate swelling. When you try to stand and put weight on the injured leg, the knee may give way and feel unstable. In most cases, you must stop physical activity due to pain or because the knee is no longer stable enough to support your weight.


Diagnosing a torn ACL

To diagnose a torn ACL, your doctor first wants to know as much as possible about how the injury occurred. Be prepared to describe:

bulletHow the injury felt and whether you heard your knee pop
bulletWhether the injury swelled immediately afterward
bulletIf you were unable to continue being physically active

All of these are signs and symptoms of a possible ACL tear.

Next, your doctor physically examines your knee to determine if the ACL is torn. Commonly used exams are the Lachman test and the pivot shift test.

Lachman test. In this test, while lying flat, you bend your knee at a 30-degree angle and the doctor gently moves your lower leg forward at the knee. If your lower leg moves forward freely without reaching a firm endpoint, your ACL is torn.


Pivot shift test. In this test, the doctor extends your knee and rotates your foot inward while applying pressure to the outside of your knee and slowly bending it. The doctor is checking for signs of instability indicated by a shifting of the shinbone on the thighbone.

These tests sometimes can't detect a torn ACL if the movement in your knee is restricted by swelling or by contraction of the muscles in the back of your upper leg. These two factors prevent accurate assessment of the forward movement of the shinbone.

X-rays won't show a torn ACL, but they may be used to check for any bone injury. An ACL tear may be associated with specific types of bone fractures that occur in the shinbone.

You may expect that you need a magnetic resonance imaging (MRI) scan of the knee to confirm that your ACL is torn. However, an MRI is relatively costly and usually isn't necessary for diagnosis of an ACL tear. In trained hands, the physical examination is as good as an MRI at diagnosing a torn ACL if your physical condition allows adequate examination.

In some cases, your doctor may order an MRI to determine if there is any damage to the protective cartilage in the knee that provides a cushion between the upper and lower leg bones (meniscus). Depending on the nature of the injury and other exam findings, an MRI can also help identify other ligament or structural damage in the knee.

Treatment options


There's no single best way to treat a torn ACL. Whether surgical treatment is right for you depends on many factors, including:

bulletHow much damage was done to your knee
bulletYour lifestyle
bulletYour willingness to modify your activities
bulletYour motivation to work through rehabilitation to strengthen the knee after surgery

Your doctor will tell you if you have any associated injuries that require surgery. If not if a torn ACL is the extent of your injury consider if the non-surgical option is acceptable to you. This means making some changes to your activities, including avoiding sports that require cutting, pivoting and jumping. If these lifestyle changes aren't acceptable to you, then discuss surgical options with your doctor.

Keep in mind that there's no advantage to having surgery immediately. You don't have to decide right away. In most cases, people who have surgery do better if they wait for the swelling to go down, exercise before surgery to regain strength and full range of motion in their knee, and then undergo surgical repair of the knee.

Before making any decision, consider the pros and cons of both non-surgical rehabilitation and surgical reconstruction in relation to what's most important to you.


Non-surgical rehabilitation

If your knee is stable during typical daily activities, the knee cartilage hasn't been damaged, and you have no desire to participate in high-risk activities involving jumping, cutting, and pivoting, you and your doctor may decide that surgery isn't necessary. You may be able to continue with your daily activities by doing physical therapy exercises, changing your activities and possibly wearing a knee brace for more moderate-risk activities.

Non-surgical rehabilitation (rehab) may also be appropriate for a child or an adolescent with a torn ACL. If your child has no damage to the knee other than to the ACL and can avoid high-risk activities, your doctor may recommend postponing surgery until your child's bones have finished growing.

As with all treatment options, you'll want to consider the trade-offs before deciding if non-surgical rehabilitation is the best choice for you.


Physical therapy: Readying a knee for life without an ACL


The goal of physical therapy is to strengthen the muscles around your knee to make up for the absence of an intact ACL. Training focuses on the muscles in the back of the thigh (hamstrings), the muscles on the front of the thigh (quadriceps), the calf, the hip and the ankle. Some exercises can be done at home. Others require the use of weight machines, exercise bicycles or treadmills, which may require visits to an athletic club, fitness center or clinic.

In the early stages of rehab, you work on re-establishing full range of motion in your knee. Then you progress to knee-, hip- and ankle-strengthening exercises combined with training to improve your stability and balance. Finally, you work on training specific to your sport or work activities, including exercises to help you prevent further injury, such as learning how to land properly from a jump.

A non-operative rehabilitation program may be easier and less painful than doing the physical therapy that's needed after surgery. You can expect to be back to your normal daily activities in as soon as three or four weeks. However, the amount of time you need to devote to physical therapy exercises can be significant, from 30 to 60 minutes on most days in the first few months after your injury. In addition, a program of strength and stability exercises for your legs should be performed two to three days a week throughout your life to maintain maximum knee stability.


Changing activities to protect your knee

You'll need to change your activities to avoid high-risk sports that could further damage your knee. Avoid activities that include jumping, cutting, pivoting and sudden slowing down or stopping (deceleration), such as basketball, football and soccer. You'll likely be able to do other activities, such as jogging, swimming and bicycling, without difficulty.

Most people who choose non-surgical rehabilitation have few symptoms five years after their injury, but that's if they stop taking part in high-risk sports, such as skiing, soccer and basketball. By doing this, they reduce their chances of having problems with the injured knee in the future. However, people who continue to participate in sports or activities that involve cutting, pivoting or sudden deceleration may find their knee giving out.

Before you decide on a course of treatment, ask yourself if you're willing to change your activities and give up those that may further damage your knee.


Knee brace: A stabilizer when you're active


A knee brace doesn't take the place of the torn ACL, but it can help stabilize your knee while you take part in activities such as skiing, tennis or hiking over uneven ground. These braces are usually custom-fitted or tailored. They can be costly and may not be covered by your insurance provider.

With the aid of a brace, most people can continue to participate in many of their previous activities that don't involve jumping or cutting and pivoting. People wearing knee braces report fewer episodes of instability or giving way, but it's not known exactly why this occurs.

You may continue to experience instability in your knee during certain types of activities, even while wearing a brace. If this happens, consider making additional changes in your activities or reconsider surgical reconstruction. These repeated events could damage the cartilage and other parts of the knee.

Pros and cons

Nonsurgical rehabilitation may be the best course of action for you, especially if you can change your lifestyle to accommodate your injury. Before deciding, consider these points:

Pros Cons
You avoid risks commonly associated with any type of surgery. You must change your activities and give up high-risk activities.
Rehabilitation may be easier and less painful than recovery and rehab after surgery. You may need to wear a knee brace to participate in certain types of activities.
You won't lose as much time from work or school, and you won't require as much help from family or friends as you would with surgery. Even with a knee brace, you may experience repeated episodes of instability during which the knee gives away.
Surgical reconstruction is still an option in the future. Over time, knee instability may cause irreparable damage to the cartilage and other parts of the knee.
  Non-surgical treatment isn't an option if you have damage to your knee cartilage that interferes with your range of motion (locked knee).


Reconstructive surgery


If your knee gives way during typical daily activities (functional instability) or if you're unable to participate in high-risk activities that are important to you, discuss surgical reconstruction with your doctor.

Your doctor may also recommend reconstruction if there's damage to the meniscus, the cartilage in the knee at the top of the shinbone. If the meniscus is torn and needs to be trimmed (partial meniscectomy), removing some of the cartilage makes the knee even more unstable. That often requires ACL reconstruction in order to regain stability in the knee. If the meniscus is repaired without reconstructing the ACL, the repair has a much higher failure rate, and arthritis in the knee may occur earlier than if the ACL is repaired at the same time.

The goal of ACL reconstruction is to give you the most stable knee possible so that you can resume your previous level of activity with a safe knee that minimizes the risk of future knee damage. About nine in 10 people who undergo ACL reconstruction report good to excellent results and are satisfied with their knee stability. Though most people return to sports activities, some don't return to their previous level of high-intensity sports activity after reconstruction and rehabilitation. They limit their activities by choice or because of pain, swelling, persistent looseness, or age-related lifestyle changes.

As with all treatment options, you'll want to consider the trade-offs before deciding if surgical reconstruction is the best choice for you.




A torn ACL doesn't heal, and attempts to repair, rather than replace, the torn ligament haven't been successful. Even if the ACL detaches from the bone without tearing, it's no longer able to function properly, even if it could be reattached.



As a result surgical treatment involves reconstructing the ACL by replacing it with another tendon (graft). A procedure that uses a tendon from your own body is called an autograft, and one that uses a tendon from another person is called an allograft (cadaver graft).

Patellar tendons or hamstrings are most commonly used. A portion of the patellar tendon the wide tendon that connects the kneecap to the shinbone or two hamstring tendons tendons on the inside of the lower thigh are used to replace the ACL.

A patellar tendon graft is performed using arthroscopic techniques. Using a small incision on the knee, the graft is taken from the middle third of the patellar tendon, including a small portion of attached bone at either end. A hole is drilled at an angle through the tibia and into the femur, following the path of the injured ACL. The graft is then threaded through the holes, and the small pieces of bone at either end of the tendon are attached to the femur and the tibia, usually with screws or staples, which are left in place permanently.


Pros and cons of different grafts


Some research has shown small differences in outcomes of patellar tendon grafts and hamstring grafts. Consider these pros and cons:

Type of graft Potential advantages Potential disadvantages
Patellar tendon graft Longer history of successful results. More frontal knee pain.
    Postoperative quadriceps weakness.
Hamstring grafts Less frontal knee pain. Postoperative hamstring weakness.
    Higher rate of follow-up surgery to remove hardware.

Not all research studies agree with these possible pros and cons. And with ever-improving surgical and rehabilitation techniques, these differences may become smaller still. Both grafts are about equal in regard to the number of people who return to their previous level of activity.

If because of your age your own tendons don't provide the best replacement for the injured ligament, your doctor may recommend an allograft. One benefit of an allograft is that recovery from surgery is usually easier, faster and less painful because you don't have to recover from the removal of the tendon used for the graft.

Allografts are taken from cadavers that have been carefully screened and tested. The risk of disease transmission is very small. From 1997 to 2001, more than 2 million musculoskeletal allografts were used without any incidence of human immunodeficiency virus (HIV) or hepatitis transmission. A few cases of bacterial infection from allografts occurred, but the incidence is still low.

Some types of synthetic grafts have been tried either as a replacement for the ACL or to supplement a natural graft. But synthetic grafts have a high failure rate, and synthetic supplemental grafts show no advantage over biological grafts.


Consider potential complications


As with any surgery, you'll want to consider some potential complications before deciding on ACL reconstruction:

bulletPain in the front of the knee occurs in some people who have ACL reconstruction. Making changes to the physical therapy program usually can control this.
bulletLimited range of motion occurs in a small number of people after surgery, often because of inadequate placement of the graft. In rare cases, this may require a second surgery to correct.
bulletA small percentage of people experience increased motion in the knee, sometimes referred to as a loose graft. This may be related to stretching of the graft over time or re-injury.
bulletOccasional swelling of the knee can occur despite a successful ligament reconstruction.



After ACL surgery your knee may be placed in a splint or brace for your comfort and protection. Most people go home on the day of surgery and use crutches for several weeks. This first week at home can be challenging because your mobility is restricted and your typical daily activities are more difficult. During this period you're largely dependent on others, so it's important that you have someone at home who can help.

It typically takes six to nine months of physical therapy and strengthening exercises before you'll be able to return to your previous level of activity. You'll need to do a lot of work that will take a significant amount of your time. It's important that you have the motivation needed to complete the rehabilitation program before deciding to have surgery.

Expect your rehabilitation to occur in three phases. Progression from one phase of rehab to the next depends on the nature of your particular injury and how well you master the goals within each phase. Your rehab may be shorter or longer than this example:

Phase 1. The first phase of postoperative rehabilitation begins on the first day after surgery and takes six to eight weeks. It consists of controlling the pain and swelling in the knee, regaining your range of motion and preserving muscle strength. You work with a trained physical therapist a few times a week at first, then once every week or two as you progress. On days when you don't have a therapy session, you do exercises at home for 30 to 60 minutes a day.

Phase 2. The second phase of rehab typically lasts from two to four months after surgery. During this phase, you focus on controlling swelling and recovering full muscle strength. In addition to daily strengthening exercises, you begin working on stability and balance training. You see the physical therapist less often, but you continue with 30 to 60 minutes of exercises each day.

Some exercises require the use of weight machines, exercise bicycles or treadmills that you might do in a supervised clinic setting. Depending on the facilities available where you receive treatment and the number of physical therapy visits allowed by your insurance provider, you may need to visit an athletic club or fitness center to do some of the exercises.

Phase 3. The final phase of postoperative rehab lasts from four to eight months after surgery and consists of a gradual return to full activity. This requires full motion, normal muscle strength and the absence of swelling. You'll continue with stability, balance and strength training as well as training specific to your sport or work activities. This may include exercises to help you prevent further injury, such as learning how to land properly from a jump.

After ligament reconstruction and rehabilitation, you should be able to return to full activity without a brace. It's important not to try to return to full activity too soon because the knee may become inflamed or re-injured. The graft needs to heal, and too much stress before it's completely healed may increase the risk of the graft failing.

Pros and cons

Reconstructive surgery may be the best course of action for you, especially if you aim to return to the same activities you participated before your injury. Before deciding, consider these points:

Pros Cons
Successful reconstruction and rehabilitation can allow you to return to full activities with a healthy knee. Surgery and anesthesia carry risks, including infection.
After rehab, you should be able to participate in sports without the use of a brace and experience no episodes of instability in which the knee gives away. Immediately after surgery, your mobility is restricted and daily activities are difficult. This can have a significant impact on your work and family.
The grafted ligament eventually becomes as strong as or even stronger than the original ACL. Graft failure, at worst, is less than 5 percent. Rehab after surgery is more work than non- surgical rehab. Recovery from surgery can be painful, and the postoperative rehabilitation program can be strenuous and time-consuming.
  The financial cost of surgery and rehabilitation can be significant.


Things to consider

Choosing what's best for you means weighing all of the options in relation to your values and your own situation. As you make the decision about how to treat your ACL injury, here are some issues to consider and questions to ask yourself.

What kinds of activities do you want to participate in? How important are these activities to you? Are you willing to modify your lifestyle to avoid cutting, pivoting, and jumping activities that put your knee at risk? Consider your stage in life and the kinds of activities that are important to you. If you can change your activities to eliminate high-risk sports, you may do well without reconstruction. Many people continue to participate in sports such as skiing, tennis and bicycling without reconstruction. They support their knee by wearing a brace.

On the other hand, if it's important to you to be involved in activities that involve leg impact and require pivoting, cutting, and jumping such as basketball, football or soccer it will be hard for you to compensate without ACL reconstruction.

Are you able to function in your normal daily activities without your knee giving way? People who have no instability no instances where the knee gives way or pops out can do well without surgery by strengthening the muscles around their knee to improve their balance and stability. Some people with a torn ACL, however, have episodes of knee instability when performing such routine daily activities as stepping off a curb or stepping out of the shower. If your knee gives way during your typical daily activities, you may need to consider reconstruction.

Are you willing to do the rehabilitation exercises needed after surgery? Recovery and rehab after surgery is more difficult and painful than nonsurgical rehabilitation. Recovery from surgery can be quite painful, and the first 2 weeks after surgery are especially difficult for most people. The success of ACL reconstruction depends on your motivation and willingness to participate in the rehabilitation program. Surgery alone won't fix your knee. The end result of your treatment is dramatically affected by your commitment to your rehab. If you're unwilling to do the rehabilitation work needed, you probably shouldn't have reconstructive surgery.

How will having knee surgery affect your family and your job? After surgery, your mobility is restricted and your daily activities are more difficult. You depend on others for help, and you're unable to help them in ways you usually do. Consider the timing of your surgery in order to minimize the effect on work and family. Don't rush into surgery. By waiting and doing some preoperative rehab, you may even improve the outcome of your ACL reconstruction.

Does your surgeon have significant experience with ACL reconstruction? If you decide to have your ACL repaired, your chances for a successful outcome are greater if the operation is performed by a surgeon who has done this type of surgery many times before.



allograft. Tissue transplanted into one person from another.

anterior cruciate ligament (ACL). The ligament that attaches the bottom of the thighbone (femur) to the top front of the shinbone (tibia).

arthritis. A chronic condition characterized by pain and swelling of the joints.

arthroscopy. Examination of a joint with a lighted viewing instrument inserted through a small incision in the skin.

autograft. Tissue transplanted from one part of a body to another part of that body.

cadaver. A dead body.

cartilage. Bloodless connective tissue found in the joints, ears and nose.

collateral ligaments. The two ligaments, one on each side of the knee, that in conjunction with the ACL and PCL attach the thighbone (femur) to the shinbone (tibia).

femur. Thighbone.

graft. Tissue or organ transplanted from one part of a body to another part of that body, or from one person to another.

hamstring tendon. One of three tendons that are part of the hamstring muscles.

hamstrings. The three muscles on the back of the thigh.

hepatitis. Inflammation of the liver. Some forms are caused by viruses.

human immunodeficiency virus (HIV). The virus that causes acquired immunodeficiency syndrome (AIDS).

Lachman test. (LAK-mun test) Used for diagnosing ACL injuries. With the knee bent slightly, the tibia (shinbone) is moved forward at the knee. With an intact ACL, the tibia should reach a firm endpoint.

ligament. Connective tissue that attaches bone to bone or bone to cartilage.

menisectomy. (men-i-SEK-tuh-me) Surgical removal of all or part of the meniscus.

meniscus. (muh-NIS-kus) The crescent-shaped cartilage in the knee that provides a cushion between the thighbone (femur) and the shinbone (tibia).

magnetic resonance imaging (MRI). Technology that uses magnetically induced radio waves to produce detailed, three-dimensional images of the body for diagnostic purposes.

patella. (puh-TEL-uh) The kneecap, or bone at the front of the knee.

patellar tendon. (puh-TEL-uhr TEN-dun) Tendon that attaches the kneecap (patella) to the shinbone (tibia).

patellofemoral. (puh-tel-o-FEM-uh-rul) Related to the kneecap (patella) and thighbone (femur).

physical therapist. A person trained and licensed to help in the diagnosis and treatment of physical disabilities.

physical therapy. The treatment of disorders that uses exercise, heat or cold, water therapy and other methods to promote the regaining of function after an illness or injury.

pivot shift test. Used for diagnosing ACL injuries. With the knee extended and foot rotated inward, pressure is applied to the outside of the knee while the knee is gradually bent to check for signs of the thighbone sliding against the shinbone.

posterior cruciate ligament. (pos-TERE-e-or KROO-she-ayt LIG-uh-munt) The ligament that attaches the bottom of the thighbone (femur) to the top back of the shinbone (tibia).

postoperative. Occurring after surgery.

quadriceps. The four muscles on the front of the thigh.

tendon. Tissue that connects muscle to bone.

tibia. Shinbone.


By Mayo Clinic staff