What Increases Your Risk

Things that increase your risk of anterior cruciate ligament (ACL) injuries include:

• Playing sports that involve sudden changes in direction or cutting around other players or obstacles, such as skiing, football, soccer, basketball, baseball, and tennis.
• Making accidental movements that may twist your knee. Examples include falling off a ladder, jumping from an extreme height, stepping into a hole, or missing a step on a staircase.
• Losing muscle tone in legs (from aging or inactivity).
• Having unbalanced leg muscle strength, such as if the muscles in the front of your thigh (quadriceps) are stronger than the muscles at the back of your thigh (hamstrings).
• Previous ACL injuries, especially if your knee sometimes gives out or buckles (chronic ACL deficiency).

Women have more ACL injuries than men. In sports, women injure their ACL up to 8 times as often as men.^{1, 2}

When To Call a Doctor

Call your doctor immediately if you have an injury to your knee and:

• You have severe pain in your knee.
• Your knee appears to be deformed.
• You have signs of damage to the nerves or blood vessels. Signs include numbness, tingling, a "pins-and-needles" sensation below the injury, an inability to move your leg below the injury, pale or bluish skin, or your leg feels cold.

Call your doctor today if:

• Your knee begins to swell within 2 hours of the injury.
• You hear or feel a pop in your knee during an injury.
• Your knee won't bear weight.
• You are unable to straighten your leg completely.
• Your knee is unstable, buckles, or gives out.
• Your knee "locks" in one position.
• You have had an anterior cruciate ligament (ACL) injury in the past and you have reinjured your knee.

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 nonprescription anti-inflammatory drug to reduce swelling. For more information on first aid steps, see Home Treatment.

Watchful Waiting

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.

Serious knee injuries need to be checked for possible broken bones as well as ligament or 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.

Who To See

Knee problems can be diagnosed by:

• Emergency medicine specialists (for acute knee injury).
• Family medicine doctors familiar with knee injuries.
• Orthopedic surgeons.
• Sports medicine specialists.

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.