At the time of an ACL injury, signs and symptoms may include:

• A loud "pop" sound
• Severe pain
• Knee swelling that usually worsens for hours after the injury occurs
• A feeling of instability or "giving way" with weight bearing

Once the swelling subsides, your knee may still feel unstable. It may feel as if it's going to "give way" during twisting or pivoting movements.

When to see a doctor
If you experience any of the signs and symptoms of ACL injury — a popping sound, severe knee pain, a swollen knee or a feeling that your knee is giving out — see a doctor. Also see your doctor if your knee feels loose or unable to support your weight. In general, the longer you wait to start treatment, the longer it will take to get better.

©1998-2009 Mayo Foundation for Medical Education and Research (MFMER). Terms of use.

Ligaments are strong bands of tissue that attach one bone to another. The ACL, one of two ligaments that cross in the middle of the knee, connects your thighbone (femur) to your shinbone (tibia) and helps stabilize your knee joint.

Most ACL injuries happen during sports and fitness activities. The ligament may tear when you slow down suddenly to change direction or pivot with your foot firmly planted, twisting or overextending your knee.

Sports that involve running, turning sharply, pivoting and jumping — especially basketball, soccer and gymnastics — put your knee at risk. The ACL can also tear when the tibia is pushed forward below the femur, such as during a fall in downhill skiing. A football tackle or motor vehicle accident also can cause an ACL injury. However, most ACL injuries occur without such contact.

©1998-2009 Mayo Foundation for Medical Education and Research (MFMER). Terms of use.

ACL injuries are most common among:

• Athletes. If you engage in certain sports, such as those that rely on cut-and-run techniques (basketball, soccer, football) you're more at risk of an ACL injury.
• Women. Women are significantly more likely to have an ACL tear than are men participating in the same sports. Women tend to have imbalanced thigh muscles, with stronger muscles at the front of the thigh (quadriceps), compared with those at the back of the thigh (hamstrings). The hamstrings help protect the shinbone from sliding too far forward. When landing from a jump, some women may land in a position that increases stress on the ACL.

©1998-2009 Mayo Foundation for Medical Education and Research (MFMER). Terms of use.

In the short term, you'll have to stop doing the activities that cause pain until your injured ligament has healed. You may have to take time off work, school and sports.

Other complications may include:

• Torn meniscus. In many cases, an ACL injury also results in a tear of the meniscus — the cartilage in your knee between the thighbone and shinbone. A cartilage tear increases the risk of future joint problems.
• Arthritis. A common long-term complication is the early onset of knee osteoarthritis, in which joint cartilage deteriorates and its smooth surface roughens. About half the people with an ACL tear develop osteoarthritis in the involved joint 10 to 20 years later. Arthritis may occur even if you have surgery to reconstruct the ligament.

©1998-2009 Mayo Foundation for Medical Education and Research (MFMER). Terms of use.

You're likely to start by first seeing your family doctor or a general practitioner. However, in some cases when you call to set up an appointment, you may be referred immediately to an orthopedist, an orthopaedic surgeon or a sports medicine specialist.

Because appointments can be brief, and because there's often a lot of ground to cover, it's a good idea to be well prepared for your appointment. Here's some information to help you get ready for your appointment, and what to expect from your doctor.

What you can do

• Write down any symptoms you're experiencing, including what you were doing when you first started experiencing the symptoms.
• Ask a family member or friend to join you, if possible. Sometimes it can be difficult to soak up all the information and treatment options provided to you during an appointment. Someone who accompanies you may remember something that you missed or forgot.
• Write down questions to ask your doctor.

Your time with your doctor is limited, so preparing a list of questions ahead of time will help you make the most of your appointment. List your questions from most important to least important in case time runs out. For an ACL injury, some basic questions to ask your doctor include:

• What's the most likely cause of my symptoms?
• Are there other possible causes for my symptoms?
• What kinds of tests do I need? Will these tests definitively diagnose my condition?
• What treatment options are available?
• Which do you recommend for my situation?
• If I choose not to have surgery, how long might recovery take?
• If I don't have surgery, what signs and symptoms would indicate a need for surgery?
• If I have surgery, what's the average recovery time?
• What activity restrictions do I need to follow?
• Are there any brochures or other printed material that I can take home with me? What Web sites do you recommend visiting?

In addition to the questions that you've prepared to ask your doctor, don't hesitate to ask questions during your appointment at any time that you don't understand something.

What to expect from your doctor
Your doctor is likely to ask you a number of questions. Being ready to answer them may reserve time to go over any points you want to spend more time on. Your doctor may ask:

• When did you first begin experiencing symptoms?
• What were you doing at the time?
• Did you experience immediate swelling?
• Have your symptoms been continuous, or occasional?
• How severe are your symptoms?
• Does anything seem to improve your symptoms?
• What, if anything, appears to worsen your symptoms?
• Does your knee ever "lock" or feel blocked when you're trying to move it?
• Do you ever feel that your knee is unstable or unable to support your weight?

What you can do in the meantime
If you've injured your knee, don't move the joint. Use a splint to keep your knee protected in a comfortable position until a doctor examines it. Avoid returning to a sport or activity until you've had the injury evaluated.

©1998-2009 Mayo Foundation for Medical Education and Research (MFMER). Terms of use.

To diagnose a torn ACL, your doctor first wants to know as much as possible about the injury, such as whether you heard or felt your knee pop, whether your knee swelled up afterward and if you were able to continue being physically active.

Swelling that occurs shortly after the injury usually means there's blood in the joint from torn blood vessels in the damaged ligament. Your doctor may decide to draw the blood out with a needle and syringe. This can reduce pain and make it easier to examine the knee joint.

Your doctor examines your knee in a variety of positions to assess whether or not your ACL is torn. Two common exams are:

• Lachman's test. In this test you lie on your back on the exam table with your injured leg bent at a 30-degree angle and your foot flat on the table. Your doctor then moves the lower portion of your injured leg forward from the knee. If your leg moves freely without reaching a firm endpoint, you have a tear in your ACL.
• Pivot shift test. For this test, your injured leg is extended, and your doctor rotates your foot at the same time he or she applies pressure to the outside of your knee and bends your knee. Signs of instability in your shinbone suggest an ACL tear.

Often the diagnosis can be made on the basis of the physical exam alone, but you may need X-rays to rule out a bone fracture. If your doctor has questions about the cause or extent of your injury, he or she may order a magnetic resonance imaging (MRI) scan, a painless procedure that uses magnetic fields to create an image of the soft tissues of your body. An MRI can show the extent of ACL injury and whether other knee ligaments or joint cartilage also are injured.

©1998-2009 Mayo Foundation for Medical Education and Research (MFMER). Terms of use.

Initial treatment for an ACL injury aims to reduce pain and swelling in your knee, regain normal joint movement and strengthen the muscles around your knee. You and your doctor will then decide if you need surgery plus rehabilitation or intense rehabilitation alone.

Which option is right for you depends on several factors, including the extent of damage to your knee and your willingness to modify your activities. When a young child whose bones are still growing injures his or her ACL, doctors may recommend postponing surgery until the child's bones have stopped growing.

Short term
To treat the acute injury:

• Use ice. When you're awake, try to ice your knee at least every two hours for 20 minutes at a time.
• Elevate your knee.
• Take pain relievers such as ibuprofen (Advil, Motrin, others) as needed.
• Wrap an elastic bandage around your knee.
• Use a splint or walk with crutches if needed.
• Work with a physical therapist on range-of-motion and muscle-strengthening exercises.

Surgery
A torn ACL can't be sewn back together. The ligament is reconstructed by taking a piece of tendon from another part of your leg and connecting it to the thighbone and shinbone (autograft). If your own tendons don't provide the best replacement for the injured ligament, your doctor may recommend using a tendon from a cadaver (allograft). The cadavers used for allografts have been carefully screened and tested for diseases.

You may consider surgery if:

• Your knee is unstable and gives way during daily activities or sports
• You're very active and want to resume heavy work, sports or other recreational activities
• Other parts of your knee, such as the meniscus or other ligaments, were also injured
• You want to prevent further injury to your knee

ACL reconstruction surgery is an outpatient procedure using arthroscopic techniques. The surgeon inserts a thin instrument (arthroscope) with a light and a small camera into one or two small incisions. This allows your surgeon to see the inside of your knee joint and make the repairs.

After surgery you'll go through a rehabilitation program. In addition to working with a physical therapist, you may wear a knee brace and you'll need to avoid activities that put undue stress on your knee. Most people can return to their sports about six months after surgery. About nine in 10 people who undergo ACL reconstruction report good to excellent results and satisfactory knee stability, according to the American Academy of Orthopaedic Surgeons.

Nonsurgical rehabilitation
A rehabilitation program without surgery involves physical therapy, modifying your activities and knee bracing. This approach can be effective as long as you're willing to give up the sports and other activities that place extra stress on your knee. You may want to consider rehabilitation alone if:

• You have a partial tear
• You don't participate in sports that involve cutting, pivoting or jumping
• Your knee isn't painful or unstable during normal activities
• You lead a fairly sedentary life
• Your knee cartilage hasn't been damaged
• You have advanced knee arthritis

©1998-2009 Mayo Foundation for Medical Education and Research (MFMER). Terms of use.

To reduce your chance of an ACL injury, follow these tips:

• Improve your conditioning. Training programs that have been shown to be effective in helping to prevent ACL injuries typically include stretching and strengthening exercises, aerobic conditioning, plyometric exercises, "jump training" and risk-awareness training. Exercises that improve balance also can help when done in conjunction with other training exercises.
• Strengthen your hamstrings (women). Women athletes should take care to strengthen and stretch their hamstring muscles as well as their quadriceps.
• Keep fit year-round. If you're on a seasonal sports team, stay conditioned all year. This will help with your balance, strength and coordination when the next season starts.
• Use proper techniques when playing sports or exercising. If your sport involves jumping, learn how to land safely. Learn to do cutting maneuvers in a crouched posture with a slight bend at the knee and hip.
• Check your gear. In downhill skiing, make sure your ski bindings are adjusted correctly by a trained professional so that your skis will release when you fall.

Using a knee brace during sports doesn't reduce your risk of injury - and may provide a false sense of security.

©1998-2009 Mayo Foundation for Medical Education and Research (MFMER). Terms of use.