What’s an ACL tear? What does it feel like?

An ACL tear is damage to the anterior cruciate ligament (ACL), located at the center of your knee. The tear may be partial (the ligament is torn a little) or total (the ligament is torn into two pieces). It will hurt if you tear your ACL. Your knee may “give out” (collapse or buckle) and you may hear or feel a pop. Typically, your knee will immediately start to swell up.

“Ligament” is what the medicine world calls the tough bands of tissue that connect bones or hold organs in place. The word “anterior” means “towards the front of the body.” Cruciate means “cross-shaped,” and in medical terms it refers to the two ligaments in your knee that form the shape of a cross: the ACL in the front and the posterior cruciate ligament (PCL) in the back.

What’s the anterior cruciate ligament (ACL)?

Your knees are made up of bones, ligaments, tendons and cartilage. The anterior cruciate ligament (ACL), which is located in the front center of your knee, connects the thigh bone (femur) to the shin bone (tibia). It is one of four primary ligaments located in your knee:

  • Anterior cruciate ligament (ACL).
  • Medial collateral ligament (MCL).
  • Lateral collateral ligament (LCL).
  • Posterior cruciate ligament (PCL).

The main function of the ACL is to stop forward movement and rotation of the shin bone on the thigh bone.

What are the types of ACL tears?

When you hurt a ligament, your healthcare provider may grade the injury on a one to three scale, with three being the most severe:

  • Grade One: Your ligament has been stretched, but it still does its job of stabilizing the knee joint.
  • Grade Two: Your ligament has been stretched and loosened. It’s partially torn. (This grade is rare.)
  • Grade Three: Your ligament is torn – divided into two pieces. This is a very severe injury.

ACL tears are often accompanied by injuries to the collateral ligaments, joint capsule, articular cartilage or the menisci (cartilage pads).

How common are ACL tears? Who is at risk?

ACL tears are a very common knee injury. In the United States there are between 100,000 and 200,000 incidents every year. They’re common in athletes, especially those who do start-stop, sudden change in direction sports like football, basketball, soccer and volleyball. You’re also at a higher risk if you work a strenuous job that requires climbing, pivoting or jumping.

An ACL tear can happen to anyone at any age, but females are four times more likely to have an ACL tear than males. Experts have yet to agree on why females are more prone. Some think this is because of different physical conditioning, neuromuscular control, or muscle strength. Others think that it’s because of a difference in pelvis and lower leg alignment, looser ligaments, or how estrogen affects a woman’s ligaments. Differences in how women jump and land could also be a factor.

Can you walk with a torn ACL?

Some people feel stable enough to walk, as long as they do it slowly and carefully. Others choose to use crutches in case their knee “gives out” (collapses or buckles).

Do ACL tears hurt?

Yes. You will feel pain and may hear or feel a pop when the injury happens.

What happens if a child tears their ACL?

Children and adolescents are still growing. Reconstructing an ACL risks growth plate injury, and that can lead to bone growth problems. Sometimes the surgeon won’t operate on the ACL until the child is older and their bones are mature, of they’ll use special techniques to avoid damage to the growth plate.

What causes ACL tears?

Most ACL tears are non-contact injuries. This means that they are not caused by, for example, another player kicking your knee. They can occur in several different ways, including when you:

  • Suddenly stop running.
  • Slow down when you’re running.
  • Land awkwardly from a jump.
  • Change direction suddenly, twisting your knee.
  • Collide with someone else, like during a football tackle.

Sometimes – about half the time – other damage happens along with ACL tears. There may be damage to other parts of the knee such as the other ligaments and/or the cartilage (a gel-like connective tissue). 70 % of people with ACL tears will have injury to one or both of the menisci (the cushions in the knee that help to protect the cartilage).

What are the signs and symptoms of an ACL tear?

When your ACL tears, you might feel or hear a pop in your knee, or feel like your knee has “given out.” Other symptoms include:

  • Pain.
  • Swelling that starts immediately (but can start four to six hours after the injury) and lasts for two to four weeks.
  • Loss of range of motion in your knee.
  • Tenderness.
  • Discomfort when you walk.

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