An ACL injury is the tearing of the anterior cruciate (KROO-she-ate) ligament, or ACL, inside your knee joint. An ACL injury most commonly occurs during sports that involve sudden stops and changes in direction — such as basketball, soccer, tennis and volleyball.
Immediately after an ACL injury, your knee may swell, feel unstable and become too painful to bear weight. Many people hear a “pop” in their knee when an ACL injury occurs.
Depending on the severity of your ACL injury, treatment may include surgery to replace the torn ligament followed by rehabilitation exercises to help you regain strength and stability. If your favorite sport involves pivoting or jumping, a proper training program can help you to reduce your chances of an ACL injury.
At the time of an ACL injury, signs and symptoms may include:
When to see a doctor
Most people seek immediate medical attention after an ACL injury.
Ligaments are strong bands of tissue that connect 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.
Landing awkwardly from a jump can also injure your ACL, as can falls during downhill skiing. A football tackle or motor vehicle accident also can cause an ACL injury. However, most ACL injuries occur without such contact.
Women are significantly more likely to have an ACL tear than are men participating in the same sports. Women tend to have a strength imbalance, with the muscles at the front of the thigh (quadriceps) being stronger than the muscles at the back of the thigh (hamstrings). The hamstrings help prevent the shinbone from sliding too far forward. When landing from a jump, some women may land in a position that increases stress on their ACL.
People who experience an ACL injury are at higher risk of developing knee osteoarthritis, in which joint cartilage deteriorates and its smooth surface roughens. Arthritis may occur even if you have surgery to reconstruct the ligament.
The pain and disability associated with an ACL injury prompt many people to seek immediate medical attention. Others may make an appointment with their family doctors. Depending upon the severity of your injury, you may be referred to a doctor specializing in sports medicine or orthopedic surgery.
What you can do
Before the appointment, you may want to write down the answers to the following questions:
What to expect from your doctor
During the physical exam, your doctor will check your knee for swelling and tenderness — comparing your injured knee to your uninjured knee. He or she also may move your knee into a variety of positions, to help determine if your ACL is torn.
Often the diagnosis can be made on the basis of the physical exam alone, but you may need tests to rule out other causes and to determine the severity of the injury.
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 rehabilitation alone. The choice depends on several factors, including the extent of damage to your knee and your willingness to modify your activities.
Athletes who wish to return to sports involving cutting, pivoting or jumping usually pursue surgical reconstruction to prevent episodes of instability. More-sedentary individuals usually can maintain knee stability with rehabilitation alone.
Rehabilitation therapy will be needed, whether or not you have surgery on your knee. Therapy will include:
Surgical and other procedures
If you choose nonsurgical treatment for your ACL injury, you should avoid future participation in sports activities that involve a lot of cutting, pivoting or jumping.
Self-care treatments you can utilize at home include:
To reduce your chance of an ACL injury, follow these tips:
Wearing a knee brace has not been found to be helpful in preventing ACL injuries.