What is an ACL Injury?

What is an ACL injury? An ACL injury is a sprain or tear of the Anterior Cruciate Ligament (ACL) — a strong band of tissue that helps connect the femur (thigh bone) to the tibia (shinbone). Usually, ACL injuries occur while engaging in sports that involve sudden stops/changes in direction, and jumping or landing, such as basketball, football, soccer, and downhill skiing.

ACL Injury Symptoms

The symptoms of an ACL injury include:

• A loud pop when the ACL injury occurred
• A “popping” sensation in the knee
• Inability to continue activity
• Rapid swelling
• Severe pain
• A feeling of instability when bearing weight
• Loss of range of motion

Causes of ACL Injury

Knee InjuryYour ACL is one of two ligaments (bands of tissue which connect one bone to another) which cross the middle of the knee. It connects the thighbone to the shinbone and helps stabilize the knee joint. ACL injuries usually happen during sports or fitness activities that put stress on the knee. Below are the common causes of ACL injuries.

• Stopping suddenly
• Suddenly slowing down and changing direction
• Pivoting with the foot firmly planted
• Having a collision (e.g., a football tackle) or receiving a direct blow to the knee
• Landing awkwardly from a jump

When the ligament is damaged, there may be a partial or complete tear of tissue. A mild injury might stretch your ligament, but leave it intact.

Risk Factors for ACL Injuries

BasketballBesides knowing what is an ACL injury, you should know the risk factors that could increase its possibility, such as:

• Participating in certain sports, such as basketball, football, soccer, gymnastics, or downhill skiing
• Poor conditioning
• Being female (possibly due to difference in muscle strength, anatomy, or hormonal influences)
• Using faulty movement patterns
• Wearing footwear that does not fit properly
• Playing on artificial turf
• Using poorly maintained sports equipment

ACL Injury Diagnosis

During the physical examination, the doctor will check the knee for tenderness and swelling. He/she may move your knee into different positions, assessing the range of motion and overall function of the joint.

Usually, a diagnosis can be made based on the physical exam, but tests may be needed to determine severity of the injury and rule out other causes. These tests may include:

• X-rays
• Magnetic resonance imaging (MRI)
• Ultrasound

Treatment for an ACL Injury

Prompt first aid can reduce pain and swelling after an injury to the knee. You can follow the R.I.C.E. model of self-care.

• Rest – Rest is necessary for healing. It also limits weight bearing on the knee.
• Ice – When you are awake, you can ice your knee at least every 2 hours (20 minutes at a time).
• Compression – Wrap an elastic bandage/compression wrap around the knee.
• Elevation – Lie down with the knee propped up on pillows.


Treatment for ACL injuries starts with several weeks of rehabilitative therapy. The physical therapist will teach you exercises that can be performed with continued supervision or at home. To avoid putting weight on the knee, you may wear a brace to stabilize the knee and use crutches for a while. The goals of rehabilitation are to reduce pain and swelling, restore the knee’s full range of movement, and strengthen muscles.


The doctor may recommend surgery if:

• The fibrous cartilage or more than one ligament in the knee is injured
• The injury is causing the knee to buckle when doing everyday activities
• You’re an athlete and want to continue your sport (especially if it involves jumping/cutting/pivoting)

During ACL reconstruction, the surgeon will remove the damaged ligament and replace it with a segment of tendon or replacement tissue (graft). The surgeon can use a piece of tendon from your knee or a tendon from a donor.

After surgery, you will undergo another course of rehabilitative therapy. A successful ACL reconstruction, together with rigorous rehabilitation, usually can restore function to your knee.

How to Prevent ACL Injuries

Proper training and exercise can reduce the risk of ACL injuries. They include:

• Exercises to strengthen the core
• Proper warm-up before engaging in sports
• Exercises that strengthen leg muscles
• Training that emphasizes proper knee position and technique when jumping and landing
• Training to improve technique when pivoting and cutting


Consult your doctor and seek immediate care if you suffer an injury that shows signs and symptoms of an ACL injury. The knee is a complex structure of bones, tendons, ligaments, and tissues. It’s important, therefore, to get an accurate diagnosis and get proper treatment. Now that you know what is an ACL injury, you can take steps to prevent it from happening.

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