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An Overview of ACL Tears

Medically reviewed by Health Library. Date Last Reviewed: 22/05/2023

An anterior cruciate ligament (ACL) tear is an injury of the knee joint, and it usually happens while playing sports. It causes leg pain and instability of the knee. ACL tears are often seen in high-profile athletes such as football player Tom Brady, golfer Tiger Woods, and soccer player Frankie Hejduk. This is also one of the most common injuries among recreational athletes of all ages.

An ACL tear is diagnosed by a physical examination. You may need an imaging study such as an X-ray to determine whether you also have other injuries (like a bone fracture).

Depending on the extent of your injury and the severity of your symptoms, you may need treatment with physical therapy, a supportive brace, or surgery. Often, rehabilitation is part of recovery after surgical treatment.


You may hear a sudden pop and/or feel a sudden shift in your joint at the time of an ACL injury. Most people are surprised at how loud the pop can be, and sometimes bystanders can even hear it on the sideline of a football or soccer game.

Right after an ACL tear, you can rapidly develophemarthrosis (bleeding into your joint). This causes swelling, redness, warmth, bruising, pain, and a bubbling sensation in the joint.

What to Look For

The signs and symptoms of an ACL injury are not always the same, so it is important to see a healthcare provider if you experience any of the following:

Knee pain or swelling that lasts more than 48 hours

Trouble standing or walking on the affected knee

Inability to support your weight on the affected knee

A deformed or odd appearance of one side of your knee

With an ACL tear, yourjoint will be unstable and have a tendency to give out. This can occur when you are participating in sports or even with simple movements like walking or getting into a car.

Sports Ability After an ACL Tear

Athletes often have difficulty after experiencing an ACL injury. Sports like soccer, football, and basketball rely on your ACL to perform common maneuvers such as cutting, pivoting, and sudden turns.

For this reason, athletes often choose to undergo surgery in order to return to their previous level of competition.


An ACL tear is most often a sports-related injury. ACL tears can also occur during rough play, motor vehicle collisions, falls, and work-related injuries.

About 60 to 70% of ACL tears occur without contact with another athlete. Typically, an athlete suddenly changes direction (cutting or pivoting), which causes excessive stretching and tearing of the ligament.


A ligament is a strong band of connective tissue that attaches bones to each other, providing stability.

The ACL is one of four major knee ligaments. Along with the posterior cruciate ligament and the medial and lateral collateral ligaments, the ACL helps provide stability for your knee. The ACL is located in front of your knee and, along with your posterior cruciate ligament, it forms a criss-cross shape across the lower surface of your thigh bone and the upper surface of your shin bone to stabilize them.

When this ligament is stretched or pulled by your leg movements, it can rip. The size of the injury varies from a slight tear of connective tissue fibers to a complete tear and detachment.

ACL Tears in Women

Female athletes are especially prone to ACL tears. Research has shown up to an eight-fold increase in the number of ACL tears in female athletes compared with their male counterparts.

The reason for the increased risk has been debated for decades, and experts now believe that it is caused by differences in neuromuscular control. Men and women position the knee differently during critical sports movements such as landing, cutting, and pivoting. The differences in male and female anatomy and hormone levels may also factor into the different rates of ACL tears.


The diagnosis of an ACL tear relies on several methods. Along with listening to your symptoms, your healthcare provider will perform a physical examination and assess your knee mobility, strength, and swelling.

Your healthcare provider can evaluate the ligaments of your knee with specialized maneuvers that test the stability of your knee, including:

Lachman test:The Lachman test is performed to evaluate the forward movement of your tibia (shin bone). By pulling the tibia forward, your healthcare provider can feel for an ACL tear. Your knee is held slightly bent (about 20-30 degrees) and your femur (thigh bone) is stabilized while your tibia is shifted.

Drawer test:The Drawer test is performed with your knee held with a 90-degree bend. Your tibia is shifted forward and back to assess your ACL by pulling forward and your PCL is assessed by pushing back.

Pivot shift maneuver:The pivot shift is difficult to perform in the office, and it is usually more helpful in the operating room under anesthesia. The pivot shift maneuver detects abnormal motion of the knee joint when there is an ACL tear present.

During your physical examination, your leg strength and your other major knee ligaments will also be assessed.

Imaging Tests

You may also need to have an X-ray of your knee, which can identify bone fractures. A magnetic resonance imaging (MRI) study may also be used to determine whetheryour ligament is torn, whether you have sustained damage to your cartilage, and to look for signs of other associated injuries in the knee.

Keep in mind that while MRI studies can help in diagnosing injuries in and around your knee, an MRI is not always needed to diagnose an ACL tear.

Along with evaluating you for an ACL tear, your healthcare provider's assessment is also focused on identifying other injuries that may have occurred when you had your injury.

Grading ACL Tears

ACL sprains are graded based on how much the ligament is damaged.

A Grade 1 sprain is a minor stretching to the ligament and your knee is still fairly stable.

A Grade 2 is a partial ACL tear, with the ligament stretched so much that it is loose and damaged. These are relatively rare.

Meanwhile, in the more common Grade 3 sprain, there is a complete tear of the ACL, with the knee joint becoming unstable and surgery almost inevitable if it is to be corrected.


Many people who experience an ACL tear start to feel better within a few weeks of the injury. Most people do not need surgery after an ACL tear, especially if the ACL was only partially torn. If you don't playsports, and if you don't have an unstable knee, then you may not need ACL surgery.

Conservative Management

If you had a partial ACL tear, you may benefit from conservative management, which can include a combination of rest, pain control, and management of the swelling. Eventually, you can start physical therapy and/or use a knee brace. Physical therapy for a partial ACL tear includes strengthening exercises, balance exercises, and range of motion exercises.

Nevertheless, even if you don't experience any pain, you might continue to have persistent symptoms of knee instability. There are several important factors to consider when making a decision about ACL surgery. You need to consider the frequency and the severity of your symptoms and whether you are prepared to undergo surgery and postoperative rehabilitation and healing.


The usual surgery for an ACL tear is called an ACL reconstruction. A repair of the ligament is not usually possible, so the ligament is reconstructed using another tendon or ligament.The are severaldifferent approaches to ACL surgery, and your healthcare provider will explain which of these is best for you. For example, several types of graft can be used to reconstruct the torn ACL. Your practitioner can use one of your own ligaments or you can use a donor graft. Typically, using your own ligament results in stronger healing.

There are also variations in the procedure, such as the new 'double-bundle' ACL reconstruction.Risks of ACL surgery include infection, persistent instability, pain, stiffness, and difficulty returning to your previous level of activity.

Healing of an ACL Graft Takes Time

After surgery, it is important that the graft has time to heal or else it can fail. This process can take months.

The good news is that most people do not have any complications after ACL surgery.

Post-Surgical Rehabilitation

Post-surgical rehabilitation is one of the most important aspects of healing. Exercises focus on restoring motion and strengthand improving the stability of the joint to prevent future injuries.You can learn to do some exercises on your own while advancing at a steady pace.

Progressing too quickly or too slowly can be detrimental to your overall results from surgery, so it's important that you continue to work under the guidance of your therapist and your healthcare provider throughout your recovery.


You may need to use a knee braceafter ACL reconstruction surgery. These braces are designed to limit your range of motion, help stabilize your knee, and allow your ACL to heal the way that it should.

Not everyone needs a knee brace after surgery, and this decision is based on how much support your knee needs while healing.

Kids & Surgery

The decision about ACL surgery for children requires consideration of a number of factors that are not relevant for adults.Surgery increases the risk of growth problems in children. ACL surgery can cause growth plate disruptions, such as early growth plate closure or alignment deformities.

Childhood ACL Surgery

You and your child's healthcare provider will have to weight the risk of surgically induced growth plate problems with the risk of permanent knee damage if the ACL is not fixed.

A Word From Health Library

Preventing ACL tears is important. You may be at a higher risk of having a tear if you are an athlete or if you have already had an ACL tear before, even if it was surgically repaired.

Neuromuscular training may help improve your muscle control and reduce your chances of sustaining these types of injuries.

If you have had an injury, it is important that you wait long enough to heal before you return to playing. This can be difficult, especially for professional athletes and students who have athletic scholarships. Experts recommend waiting six to 12 months after a major ACL injury before returning to play. In the meantime, it is important to continue safely training so that your muscles will stay strong and so you won't experience muscle atrophy.

This information is not intended as a substitute for professional medical care. Always follow your healthcare professional's instructions.