Home > Health Library > Anterior Cruciate Ligament (ACL) Injuries
An anterior cruciate ligament, or ACL, injury is a tear in one of the
ligaments that joins the upper leg bone with the lower
leg bone. The ACL keeps the knee stable.
Injuries range from mild, such as a small tear, to
severe, such as when the ligament tears completely or when the ligament and
part of the bone separate from the rest of the bone.
treatment, the injured ACL is less able to control knee movement, and the bones
are more likely to rub against each other. This is called chronic ACL
deficiency. The abnormal bone movement can also damage the tissue (cartilage) that covers
the ends of the bones and can trap and tear the pads (menisci) that
cushion the knee joints. This damage can lead to
Sometimes other knee
ligaments or parts of the knee are also injured. This includes cartilage such
as the menisci, or bones in the knee joint, which can be
Your ACL can be injured
if your knee joint is bent backward, twisted, or bent side to side. The chance
of injury is higher if more than one of these movements occurs at the same
time. Contact (being hit by another person or object) also can cause an ACL
An ACL injury often occurs during sports. The injury can
happen when your foot is firmly planted on the ground and a sudden force hits
your knee while your leg is straight or slightly bent. This can happen when you
are changing direction rapidly, slowing down when running, or landing from a
jump. This type of injury is common in soccer, skiing, football, and other
sports with lots of stop-and-go movements, jumping, or weaving. Falling off a
ladder or missing a step on a staircase are other likely causes. Like any other
body part, the ACL becomes weaker with age. So a tear happens more easily in
people older than age 40.
Symptoms of an acute ACL
After an acute injury, you will probably have to stop
whatever you are doing because of the pain, but you may be able to walk.
The main symptom of chronic ACL deficiency is the knee buckling or
giving out, sometimes with pain and swelling. This can happen when an ACL
injury is not treated.
Your doctor can
tell whether you have an ACL injury by asking questions about your past health
and examining your knee. The doctor may ask: How did you injure your knee? Have
you had any other knee injuries? Your doctor will check for stability,
movement, and tenderness in both the injured and uninjured knee.
You may need
X-rays, which can show damage to the knee bones. Or
you may need other imaging tests, such as an
MRI. An MRI can show damage to ligaments,
tendons, muscles, and knee cartilage.
Arthroscopy may also be done. During arthroscopy, your
doctor inserts surgical tools through one or more small cuts (incisions) in the
knee to look at the inside of the knee.
Start first aid right away.
These first-aid tips will reduce swelling and pain. Use the RICE method. The
letters stand for Rest the knee, put Ice on it, use an elastic bandage to give gentle
Compression to the knee, and Elevate the leg by propping it up above the level of your
heart. And at first it's also important to move your leg as little as possible. Take
over-the-counter pain medicine.
You may need to walk with
crutches and use a knee immobilizer to keep your knee still for the first few
days after the injury.
Your knee will need to be checked by your
doctor. It's important to get treatment. If you don't, the injury may become a
long-lasting problem. There are two ways to treat the injury:
If you have surgery, you will also have several months of
Your treatment will depend on how much of the
ACL is torn, whether other parts of the knee are injured, how active you are,
your age, your overall health, and how long ago the injury occurred.
There are three main treatment goals:
The best way to
prevent ACL injuries is to stretch and strengthen the leg muscles, especially
the front and back muscles of the thigh (quadriceps and hamstrings).
Here are other things you can do that may help prevent ACL injuries:
Learning about anterior cruciate ligament (ACL) injuries:
Living with an ACL injury:
Health Tools help you make wise health decisions or take action to improve your health.
Anterior cruciate ligament (ACL) injuries are caused when the knee is straightened beyond
its normal limits (hyperextended), twisted, or bent side to side.
Typical situations that can lead to ACL injuries include:
Inactive people and some older adults who have weak leg
muscles may injure their knees during normal daily activities. But they usually
injure bones, not ligaments.
When contact causes an ACL injury, it
can be from playing a sport, from a sudden and severe accident, or from less
obvious contact injuries.
Symptoms of a severe and sudden (acute)
anterior cruciate ligament (ACL) injury
After an acute injury, you will almost always have to stop
the activity you are doing, but you may be able to walk.
Other health problems can cause symptoms like those of an ACL injury. They include a bone break or injuries to the knee cushions (menisci) or to other ligaments in the knee.
For more information on knee injuries, see:
symptom of chronic (long-lasting and recurrent)
ACL deficiency is an unstable knee joint. The knee buckles or gives out,
sometimes with pain and swelling. This happens more often over time. But not
everyone with an ACL injury develops a chronic ACL deficiency.
If you have a sudden (acute) anterior cruciate ligament (ACL) injury, you typically know when it happens. You may feel or hear a pop, and the knee may give out, causing you to fall. The knee swells and often is too painful or unstable for you to continue any activity.
An ACL injury can cause small or medium tears of the ligament, a complete tear of the ligament (rupture), a separation of the ligament from the upper or lower leg bone (avulsion), or a separation of the ligament and part of the bone from the rest of the bone (avulsion fracture). When any of these occur, the lower leg bone moves abnormally forward on the upper bone, with a sense of the knee giving out or buckling.
How an anterior cruciate ligament (ACL) injury
is treated and how it heals depends on:
An ACL injury may develop into long-lasting and
ACL deficiency that leads to an unstable knee—the knee buckles or gives out,
sometimes with pain and swelling. This can occur if you had an ACL injury in the
past and didn't know it or if your ACL has not been
treated or has been treated unsuccessfully. ACL deficiency can cause damage to the joint,
osteoarthritis. But not everyone with an ACL injury
gets ACL deficiency.
People with minor ACL injuries usually begin treatment with
a physical rehab program. Rehab exercises build strength and
flexibility in the muscles on the front of the thigh (quadriceps) and
strengthen and tighten the muscles in the back of the thigh (hamstrings). Most people return to their normal activities after a few weeks of
More serious ACL injuries may need several
months of rehab or surgery followed by several months of
rehab to regain your knee strength, knee stability, and range of
Not all ACL injuries require surgery. But whether you have
surgery or not, you need to start strengthening your knee and regaining motion
soon after you injure it. This prepares you for your rehab program if
you choose not to have surgery. It also helps prepare the knee for surgery if
you choose to have it.
Things that increase your
anterior cruciate ligament (ACL) injuries
Women have more ACL injuries than men.1
Call your doctor immediately if you have an injury to your knee and:
Call your doctor today if:
Before your appointment, don't put weight on the injured
knee. Use crutches if you need to.
Apply ice and wrap your knee in an elastic bandage or
neoprene (synthetic rubber) sleeve. Rest and elevate the knee. Take a
nonsteroidal anti-inflammatory drug, such as ibuprofen (Advil) or naproxen (Aleve), to reduce
swelling. For more information on first aid steps, see Home Treatment.
Watchful waiting is a period of time during
which you and your doctor observe your symptoms or condition without using
medical treatment. Watchful waiting is not appropriate if knee pain is severe;
if your knee is deformed, swells, or has limited movement immediately after an injury; or if you are unable
to bear any weight because of either pain or instability.
knee injuries need to be checked for possible broken bones as well as
cartilage damage. Whenever immediate swelling follows
an injury, there also may be torn blood vessels or damaged nerves in the knee.
Your doctor will check your knee to make sure the blood supply to your leg is
normal and the nerves are intact.
If you have occasional pain in
your knee or your knee sometimes gives way or buckles, have your doctor check
it. If you have damaged your ACL, it is important to get treatment so that your
knee is appropriately managed. This may reduce the chance that you will get
osteoarthritis in your knee.
Knee problems can be diagnosed by:
If surgery is considered, you may be referred to an
orthopedic surgeon (possibly a sports medicine
specialist) who is experienced in knee surgery.
To prepare for your appointment, see the topic Making the Most of Your Appointment.
anterior cruciate ligament (ACL) injury is diagnosed
through a medical history and a physical exam. A doctor who specializes
in knee injuries (for example, an
orthopedic surgeon or
sports medicine specialist) will usually be able to
accurately diagnose an ACL injury after:
If you see your doctor soon after your injury, the pain
and the degree of swelling and muscle tenseness may make it difficult for your
doctor to accurately diagnose the condition.
Other tests that may
help your doctor see how badly the knee is injured include:
If your knee looks red, feels warm to the touch, or is very swollen, a
knee joint aspiration (arthrocentesis) may be done. This involves removing fluid from the knee joint with a needle. It
is done to:
Local anesthetic may be injected to reduce
pain and make the knee easier to examine.
Before arthroscopy, you and
your doctor will decide what will be done if certain conditions are found. For
example, you may decide in advance that if a complete tear of the ACL is found,
it will be reconstructed during the arthroscopy. Or if a more severe condition
is found, you and your doctor may agree to discuss the condition rather than
proceeding with surgery at that time.
The goals of treatment for an anterior cruciate ligament (ACL) injury are to:
You'll need to work with your doctor to decide whether you should have several months of
rehabilitation (rehab) or surgery with rehab. Not all ACL tears need
If you know you have
injured your ACL, the first treatment consists
For more information on first aid, see Home Treatment.
What type of other treatment you have depends on:
Treatment options include:
Recovery from an ACL injury varies for each person.
Your treatment should continue until your knee is stable and strong rather than for a
certain length of time.
Treatment of ACL injuries in children and teens involves special concerns, because children's bones are still growing. Talk to your doctor about treatment choices for your child.
The best way to prevent
anterior cruciate ligament (ACL) injuries is to
stretch and strengthen the leg muscles, especially the front and back muscles
of the thigh (quadriceps and hamstrings).
may help prevent ACL injuries if you:
If you have already had an ACL injury, you can avoid
another one by:
Programs to prevent ACL injuries are available. These
programs typically emphasize injury awareness, avoidance techniques, and
stretching, strengthening, and jumping exercises to help reduce ACL
You can help prevent ACL injuries by practicing
landing with the knees bent after jumps and crouching when pivoting and
If you have an acute (sudden)
anterior cruciate ligament (ACL) injury, use the
following first aid steps to reduce pain and swelling:
After diagnosis of an ACL injury, your doctor may suggest
exercises that help strengthen your leg and increase your range of motion. They
may be the start of your nonsurgical treatment program or be used to help
prepare your knee for surgery.
Medicine is used to:
medicines such as acetaminophen (Tylenol, for example) or
nonsteroidal anti-inflammatory drugs (NSAIDs), such as
ibuprofen and naproxen, are commonly used.
Most surgery for
anterior cruciate ligament (ACL) injuries involves
replacing the ACL with tissue called a
graft. Usually an autograft (tendon tissue
taken from another part of the body) is used. Repair is also done when the ACL
has been torn from the upper or lower leg bone (avulsion). The bone fragment connected
to the ACL is reattached to the bone.
Most ACL surgery is done by
making small incisions in the knee and inserting surgical tools
through these incisions (arthroscopic surgery). Open surgery
(cutting a large incision in the knee) is sometimes required.
goals of surgical treatment for ACL injuries are
Most people who have ACL surgery
have favorable results, with reduced pain, good knee function and stability,
and a return to normal levels of activity. But some still have knee pain
and instability. Athletes and those who take part
in sports typically can return to their sports within months. But this may depend on how
intense and sports-focused the rehab was.
Before ACL surgery, strength and motion exercises are often
done to help get the knee ready for surgery and for rehab after surgery. Surgery is followed by a short period of home exercises,
increased activity, and the use of crutches for walking.
rehab program to strengthen the knee then begins. The rehab
program often lasts up to a year.
Surgery for ACL injuries in children and teens involves special concerns, because children's bones are still growing. Talk to your doctor about the benefits and risks of surgery.
Depending on how bad your injury is, surgery with
rehab may offer the best chance of making your knee stable again. It also may help you return to an active lifestyle without further pain, injury, or loss of
strength and movement in your knee.
If your injured knee gives out now and then (chronic ACL deficiency) and you continue to do activities that
require a stable knee, you may injure your knee again.
That may be another reason to consider surgery.
You will need to follow a rehab program whether or not
you have surgery. If you don't complete a rehab program, even with
surgery you may not regain full stability and function in your knee.
Other treatment for
anterior cruciate ligament (ACL) injuries includes
physical rehabilitation (rehab) to:
You may choose to treat an ACL injury with rehab
alone. If you have surgery, rehab will also be part of your
The American Academy of Orthopaedic Surgeons (AAOS)
provides information and education to raise the public's awareness of
musculoskeletal conditions, with an emphasis on preventive measures. The AAOS
website contains information on orthopedic conditions and treatments, injury
prevention, and wellness and exercise.
The National Institute of Arthritis and Musculoskeletal
and Skin Diseases (NIAMS) is a governmental institute that serves the public
and health professionals by providing information, locating other information
sources, and participating in a national federal database of health
information. NIAMS supports research into the causes, treatment, and prevention
of arthritis and musculoskeletal and skin diseases and supports the training of
scientists to carry out this research.
The NIAMS website provides
health information referrals to the NIAMS Clearinghouse, which has information
packages about diseases.
Honkamp NJ, et al. (2010). Anterior cruciate ligament injuries in adults. In JC DeLee et al., eds., Delee and Drez's Orthopaedic Sports Medicine: Principles and Practice, 3rd ed., vol. 2, pp. 1644–1676. Philadelphia: Saunders Elsevier.
Other Works Consulted
American Academy of Orthopaedic Surgeons and American Academy of Pediatrics (2010). Anterior cruciate ligament tear. In JF Sarwark, ed., Essentials of Musculoskeletal Care, 4th ed., pp. 640–646. Rosemont, IL: American Academy of Orthopaedic Surgeons.
American College of Radiology (2011). ACR Appropriateness Criteria: Acute Trauma to the Knee. Available online: http://www.acr.org/SecondaryMainMenuCategories/quality_safety/app_criteria/pdf/ExpertPanelonMusculoskeletalImaging/AcuteTraumatotheKNEEDoc2.aspx.
Amy E, Micheo W (2008). Anterior cruciate ligament tear. In WR Frontera et al., eds., Essentials of Physical Medicine and Rehabilitation: Musculoskeletal Disorders, Pain, and Rehabilitation, 2nd ed., pp. 307–313. Philadelphia: Saunders Elsevier.
Bernhardt DT (2010). Acute injuries of the knee. In SJ Anderson, SS Harris, eds., Care of the Young Athlete, 2nd ed., pp. 409–420. Elk Grove Village, IL: American Academy of Pediatrics.
Biau DJ, et al. (2007). ACL reconstruction: A
meta-analysis of functional scores. Clinical Orthopaedics and Related Research, 458: 180–187.
Gilchrist J, et al. (2008). A randomized controlled trial to prevent noncontact anterior cruciate ligament injury in female collegiate soccer players. American Journal of Sports Medicine, 36(8): 1476–1483.
April 4, 2012
William H. Blahd, Jr., MD, FACEP - Emergency Medicine & Adam Husney, MD - Family Medicine & Patrick J. McMahon, MD - Orthopedic Surgery & Freddie H. Fu, MD - Orthopedic Surgery
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