The knee is a joint where three main bones join: the femur, or thigh bone; the tibia, or shin bone; and the patella, or knee cap. Several ligaments attach to the femur and tibia and give the joint strength and stability. One of these, the anterior cruciate ligament (ACL), is in the center of the knee and limits rotation and the forward movement of the tibia. Recent studies estimate that nearly 250,000 ACL injuries occur annually in the United States.
The ACL is most often stretched or torn by a sudden twisting motion--when, for example, your feet are planted one way and your knees are turned another. You can also injure your ACL by quickly changing the direction in which you're moving; by putting the brakes on too quickly when running; or, when landing from a jump. A woman's body structure and hormones cause more force on the ligaments, increasing the likelihood of injury during sports and athletic activities.
Recognizing an ACL injury
People who play basketball, volleyball, soccer, or football, or who ski are most likely to injure their ACLs when they slow down, pivot or land after a jump.
If you injure yours, you may not feel any pain immediately. You might hear a popping noise and feel your knee give out from under you.
Within a few hours, you'll notice swelling at the knee. The knee will often hurt when you try to stand on it. It's important to keep weight off the knee until you can see your health care provider, or you may injure the knee cartilage. You should use an ice pack to reduce swelling and keep the leg elevated. If needed, use a pain reliever. If you must walk, use crutches and be sure to see a doctor right away to have your knee evaluated.
Your doctor may conduct physical tests and take X-rays and obtain an MRI to determine the extent of your ACL damage. If the ACL is only partially torn, your doctor may prescribe an exercise program to strengthen surrounding muscles and a brace to protect the knee during activity. You may or may not need surgery. Surgery can be performed to reconstruct the torn ligament from a piece (graft) of strong, healthy tissue taken from another area near the knee (autograft) or from a cadaver (allograft). If the ACL is completely torn, it may need to be replaced surgically.
Successful surgery tightens your knee and restores its stability, which helps you avoid further injury.
After ACL reconstruction, you'll need to do rehabilitation exercises to gradually return your knee to full flexibility and stability.
You also may need a knee brace temporarily and will probably have to stay out of sports for about six months to a year after the surgery.
Many ACL injuries can be prevented if the muscles that surround the knees are strong and flexible.
Prevention focuses on proper nerve and muscle control of the knee. Exercises aim to increase muscle power, balance, and improve core strength and stability.
The following training tips can reduce the risk of an ACL injury:
Train and condition year round.
Practice proper landing technique after jumps.
When you pivot, crouch and bend at the knees and hips. This reduces stress on the ACL.
Strengthen your hamstring and quadriceps muscles. The hamstring muscle is at the back of the thigh; the quadriceps muscle is at the front. The muscles work together to bend or straighten the leg. Strengthening both muscles can better protect the leg against knee injuries.