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The knee is the largest joint in the body, a complex system of bones, cartilage, ligaments, and tendons. Each part of the knee performs a specific job to help the joint function.

The anterior cruciate ligament (ACL) is one of four different knee ligaments, which connect your femur (thighbone) to your lower leg bones (tibia and fibula).

The ACL helps to control your knee’s back-and-forth movements. However, the ligament is susceptible to injury, especially in athletes. Noncontact ACL injuries are common in sports.

Read on to find out more about ACL injuries and how they’re treated.

What Is the ACL?

Your knee has four different ligaments:

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

The ACL is found inside your knee joint. It sits in the front and crosses the PCL to form an X. It controls the back-and-forth motion of your knee and keeps your tibia (shinbone) from sliding in front of the femur (thighbone).

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How Do ACL Injuries Occur?

ACL injuries can occur from direct contact (getting hit on the side of your knee). However, it is common to experience a noncontact ACL injury. These often occur with a sudden stop or change in direction, such as:

  • Landing from a jump.
  • Slowing down or stopping suddenly.
  • Changing direction quickly.
  • Overextending your knee.

“You commonly tear it in noncontact,” says Volker Musahl, MD, chief, Division of Sports Medicine, UPMC. “Your leg just does a funny twist; there’s internal rotation of the tibia and some valgus stress. Valgus stress is basically the tibia bone going away from your body and the femur bone going toward your body.”

ACL injuries are common in sports like basketball, football, skiing, and soccer, which include frequent stops and changes in direction. They often occur at the same time as injuries to other parts of the knee, such as the MCL or meniscus.

Types of ACL Injuries

ACL injuries are classified as sprains, with different grades depending on the severity:

  • Grade 1: The mildest ACL injury, grade 1 sprains involve a stretching of the ligament. The ACL still can keep your knee stable.
  • Grade 2: In a grade 2 sprain, or partial tear, your ACL is stretched to the point where it becomes loose. Your knee loses some stability.
  • Grade 3: This involves a complete tear of your ACL. The ligament is split in two, and you lose stability of your knee.

Most ACL injuries are complete or near complete tears, according to the American Academy of Orthopaedic Surgeons.

Symptoms and Diagnosis of ACL Injuries

If you injure your ACL, your symptoms may vary depending on the grade of the injury. A “popping” sound in your knee is often associated with ACL tears. Other symptoms may include:

  • Pain.
  • Swelling.
  • Instability in your knee.

Doctors usually can diagnose an ACL injury with a physical exam, comparing the injured knee to the uninjured one. A magnetic resonance imaging (MRI) scan can help confirm the diagnosis.

Treatment of ACL Injuries

Treatment of an ACL injury depends on the severity. For a grade 1 sprain, treatment may involve the RICE method (rest, ice, compression, and elevation). Over-the-counter pain relievers also may help. A severe sprain may require the use of a knee brace or crutches until you recover.

If you suffer a complete tear, it will not heal without surgery. Most ACL tears can’t be stitched back together, so surgeons typically use an individualized tendon graft to help reconstruct the ligament. The graft acts as an anchor for the new ligament to grow.

Whether you get surgery depends on the level of activity you need to return to. Athletes typically need surgery to return to their sport. People with a lower activity level may not need surgery.

ACL Recovery Process

Coming back from an ACL injury typically involves some form of rehabilitation. The process can help you regain strength and range of motion in your knee.

Recovery from a complete tear of your ACL can take a year or longer, Dr. Musahl says, because the ligament needs to heal.

“Usually the first six weeks is a healing time where some scar tissue needs to build,” Dr. Musahl says. “The graft needs to heal into the bone to anchor it. The next few weeks focus on range of motion, getting your mobility back. Then after that, it’s getting the strength back.”

After returning to sports, there’s a risk of reinjury to the same ligament or an injury to the other knee because of compensating.

Preventing ACL Injuries

It is impossible to completely prevent ACL injuries because of certain risk factors. For example, the way your bones are shaped can put you more at risk. Females also suffer more ACL injuries than males.

However, there are some ways you can try to prevent ACL injury. For some sports (such as football or skiing), wearing a knee brace can help reduce your risk.

Sports performance training — working on the way you move and jump — also may help you reduce the stress you put on your ACL, reducing your risk for injury.

ACL Care at UPMC

If you suffer an ACL injury, UPMC Sports Medicine offers world-class diagnosis, treatment, and recovery options. The UPMC Freddie Fu Sports Medicine Center has experts in several specialties, including orthopaedic surgeons, primary care sports medicine doctors, physical therapists, and more.

“With each individual injury, there are some small nuances that are different,” Dr. Musahl says. “The nice thing about our sports medicine center is we’re all working hand- in-hand there.”

To contact UPMC Sports Medicine, call 1-855-937-7678 or visit us online.

Sources

American Academy of Orthopaedic Surgeons, Anterior Cruciate Ligament (ACL) Injuries. Link

American Academy of Orthopaedic Surgeons, About Your Knee. Link

U.S. National Library of Medicine, Anterior Cruciate Ligament (ACL) Injury. Link

About Sports Medicine

Sports and physical activity bring with them a potential for injury. If you are looking to prevent, treat, or rehabilitate a sports injury – or improve athletic performance – UPMC Sports Medicine and the UPMC Sports Medicine Concussion Program can help. We serve athletes and active people of all ages and experience levels. Our experts partner with the Pittsburgh Steelers, Pittsburgh Penguins, Pitt Panthers, and about 100 other high school, college, and regional teams and events throughout Pennsylvania – working daily to build better athletes.