Definition

An anterior cruciate ligament (ACL) injury is a tear in the ACL ligament. The ACL is located in the middle of the knee joint. It connects the lower leg bone to the thigh bone. It stabilizes the knee and prevents the lower leg bone from sliding too far forward at the knee.

The ACL ligament can become strained or torn when a strong force is applied to it. This can happen during sports or other high-stress activity.

Treatment depends on the severity of the injury.

Anterior Cruciate Ligament Injury Copyright © Nucleus Medical Media, Inc.

Causes

ACL injury occurs when your knee gets twisted or during a hard landing from a jump. It can also happen with:

• Sudden stops or changes in direction
• Sidestepping or pivoting
• Direct contact

Risk Factors    TOP

ACL injuries are more common in women. Other factors that increase your chance of ACL injury include:

• Weak knee structure
• Muscle strength imbalance between the quadriceps and hamstrings
• Playing sports that require sudden changes of direction and deceleration
• Use of incorrect technique for cutting, planting, pivoting, or jumping

Symptoms    TOP

Symptoms may include:

• A popping sound at the time of the injury
• Pain and swelling in the knee
• Loss of full range of motion
• Weakness or instability in the knee
• Difficulty walking

Diagnosis    TOP

The doctor will ask about your symptoms and how you injured your knee. A physical exam will be done.

Tests may include:

• X-ray
• MRI
• Arthroscopy—a thin, lighted tube inserted through a small incision in the knee to look at the structures inside the knee

Ligament sprains are graded according to their severity:

• Grade 1—Mild ligament damage.
• Grade 2—Partial tearing of the ligament.
• Grade 3—Complete tearing of the ligament.

Treatment    TOP

Talk with your doctor about the best treatment plan for you. Recovery time ranges depending on the grade of your injury. Treatment steps may include:

Prevention    TOP

To reduce your chance of injuring the ACL, take these steps:

• Plyometrics, a form of jumping exercises, can be used to train and strengthen the leg muscles for jumping and landing.
• When jumping and landing, or turning and pivoting, your hips and knees should be bent, not straight.
• Strengthen both the quadriceps and the hamstrings.
• Maintain proper technique when exercising or playing sports.