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Anterior cruciate ligament (ACL) tears are the most common ligament injury requiring surgery. Despite being so common, ACL tears can cause serious knee damage if left untreated.

ACL tears usually happen when playing sports, especially when stopping, jumping, or changing direction suddenly.

What Is an ACL Injury?

The ACL is one of four ligaments connecting the shin bone to the thigh bone. The ACL and posterior cruciate ligament (PCL) are located in the middle of the knee and cross one another, forming an X-shape which is why they are labelled cruciate ligaments

An ACL injury is more common than a posterior cruciate ligament (PCL) injury because of where it’s positioned.

An impactful force or sudden movement can overstretch the ACL and partially or fully tear it. Complete ACL tears are more common than partial tears.

How Do You Tear Your ACL?

ACL tears often happen when people suddenly change direction. This can happen when someone pivots, lands at an awkward angle, or lands with too much force. Less commonly, a collision in a contact sport, such as a football tackle, can injure the ACL.

Soccer, basketball, skiing, and football are sports that risk ACL tears more than others.

An ACL tear can also happen outside of sports. A car accident or fall, especially from a height, can cause an ACL tear.

Can you tear your ACL without knowing it? An ACL tear isn’t an injury that comes on gradually. If you tear your ACL, you will feel pain and stiffness because the knee swells after the injury. It is very unusual to injure your ACL without symptoms.

How can you tell if you have a torn ACL?

Wondering how to know if you tore your ACL? The only way to know for sure is to see a doctor. Look for the symptoms listed below and seek medical care promptly.

What Does a Torn ACL Feel Like?

Common symptoms of a torn ACL include:

• A popping sound or sensation — Some people hear a loud pop or feel a popping sensation when they tear their ACL. But this doesn’t always happen.
• Instability — A torn ACL can make the knee feel like it’s giving out or cannot support your weight.
• Pain — The pain occurs right away, especially when you put weight on the injured leg.
• Reduced range of motion — You may be unable to straighten or bend your knee fully.
• Swelling — The knee usually swells quickly, often within a few hours, because the tear causes internal bleeding.

The feeling of instability — that the knee is wobbly or can buckle more easily — sets ACL tears apart from other knee injuries.

If you notice these symptoms after an injury, you should seek medical help right away. Ignoring them could lead to further damage or long-term knee problems.

How Do Doctors Diagnose an ACL Tear?

A doctor will start by asking you about the injury, including when it happened and your symptoms. They will then examine the knee and may move the leg in different positions to check its stability.

One common test is the Lachman test, which is performed while lying down with your knee slightly bent. Your doctor will lift your lower leg forward by pulling at the back of the shin. If the lower leg moves forward too much, that’s a sign of a torn ACL.

To confirm the diagnosis and assess the extent of the injury, your doctor may order imaging tests:

• X-rays — These are usually done to rule out broken bones; they don’t show ligaments.
• MRI — This is ideal for viewing soft tissues like ligaments. It can show whether the ACL is partially or completely torn.

What Is the Treatment for a Torn ACL?

Treatment depends on your age, your lifestyle, activity goals, how badly you tore the ACL, and any other injuries to the knee that occurred when the ACL tore.

You should see an orthopaedic specialist as soon as possible to determine the extent of your injury and the best treatment for you.

In the meantime:

• Don’t put weight on the leg if painful. Use crutches or a wheelchair, if necessary.
• Rest and elevate the knee.
• Consider an over-the-counter pain medication such as ibuprofen if the pain doesn’t improve with rest. Ask your doctor if this medication is right for you, especially if you have stomach ulcers, kidney disease, liver disease, heart failure, or bleeding disorders.
• Use cold packs (or ice wrapped in a towel) to assist with swelling. Apply for 10 to 20 minutes at a time every couple of hours.

Nonsurgical treatment

This is an option if the ACL is partially torn. People with a complete tear may also choose this option if they are older and/or don’t engage in demanding activities. It includes:

• Activity modification — You may need to avoid activities that cause the knee to twist or pivot.
• Bracing — A knee brace can provide extra support.
• Physical therapy — Exercises that strengthen the muscles around the knee can reduce the pressure on the ligaments in the knee.

ACL partial injuries can heal within three months. Your recovery time may be shorter or longer than this.

Surgery

Doctors often recommend surgery for people with complete ACL tears who want to return to sports or high-impact physical activity. Complete ACL tears won’t heal on their own. Surgery may also benefit people with partial ACL tears, helping to prevent a future repeat injury.

Your doctor may suggest physical therapy to restore knee range of motion before surgery. This increases the chance of a successful surgery.

The surgeon usually replaces the torn ACL with a tendon taken from the knee or leg. You will be under general sedation, which means you’ll be asleep during the surgery.

Recovery after surgery takes time. You’ll need to use crutches and wear a brace for the first few weeks. Swelling and pain are common.

Your doctor will refer you for physical therapy shortly after surgery to gradually improve your range of motion, balance, and strength.

Returning to sports or demanding physical activities may take six to 12 months.

Why Is It Important to Seek Medical Care for a Torn ACL?

An unstable knee after a torn ACL increases the risk of further injuries, such as damage to the cartilage. Over time, this can lead to early arthritis in the knee.

The earlier you get a diagnosis and treatment, the lower your risk of further injury. Even if surgery isn’t needed, physical therapy and other treatments can help protect your knee as it heals.