ACL Injury (Torn ACL)

First aid for a suspected ACL injury

1. Stop playing. Continuing to pivot on an unstable knee can damage the meniscus and cartilage.
2. Ice the knee for 15 to 20 minutes every 2 to 3 hours, wrapped in a cloth.
3. Compress with an elastic bandage, firm but not tight.
4. Elevate the leg above heart level.
5. Use crutches if walking is painful, and get the knee assessed within a few days.
6. Pain relief: acetaminophen (paracetamol) or ibuprofen at the label dose.

What the ACL does

The ACL runs diagonally inside the knee from the thighbone (femur) to the shinbone (tibia). It prevents the tibia from sliding forward under the femur and controls rotation. Together with the posterior cruciate ligament (PCL) and the medial and lateral collateral ligaments (MCL and LCL), it keeps the knee stable during pivoting sports.

How ACL injuries happen

About 70% of ACL tears happen without contact:

• landing from a jump with the knee straight or caving inward (knee valgus)
• sudden stopping or deceleration
• cutting or pivoting with the foot planted
• hyperextension

Contact injuries, such as a blow to the outside of the knee in football, often also damage the MCL and meniscus. High-risk sports include soccer, basketball, football, skiing, volleyball, netball and handball.

Female athletes have a 2 to 8 times higher risk than male athletes in the same sports, due to differences in landing mechanics, muscle activation, anatomy and possibly hormones.

Symptoms of a torn ACL

• a loud pop or popping sensation at the time of injury
• rapid swelling within a few hours, from bleeding into the joint
• pain deep in the knee
• inability to continue the activity
• loss of full range of motion
• instability: the knee gives way or feels loose, especially when turning

After the first swelling settles, some people can walk fairly normally on flat ground, which can falsely suggest a minor injury. The instability shows up with twisting or sports.

Grades of ACL injury

Associated injuries

About half of ACL tears come with other damage:

• Meniscus tear: the cartilage shock absorbers inside the knee
• MCL injury: the ligament on the inner side of the knee
• Bone bruises on MRI
• Cartilage damage

Multiple ligament injuries, including the PCL, are covered in knee ligament or meniscus tear.

Diagnosis

1. History: mechanism, pop, swelling and giving way.
2. Examination: the Lachman test (the clinician pulls the shin forward with the knee slightly bent) is the most accurate bedside test. The pivot shift and anterior drawer tests are also used. Exams are easier after swelling settles.
3. X-ray: to rule out fractures, including a small avulsion fracture (Segond fracture) strongly linked to ACL tears.
4. MRI: confirms the tear and shows meniscus, cartilage and other ligament injuries.

Treatment

Rehabilitation without surgery

Physical therapy focused on strength, balance and neuromuscular control can give good results for people who:

• do not play pivoting sports, or are willing to change activities
• have no recurrent giving way
• have no repairable meniscus tear

Some people successfully return to sport without surgery, and a minority later choose reconstruction if instability persists.

ACL reconstruction surgery

A torn ACL does not heal well on its own, so surgery replaces it with a graft, usually taken from your own:

• patellar tendon (bone-tendon-bone)
• hamstring tendons
• quadriceps tendon

Donor (allograft) tissue is an option, mainly for older or less active patients, as it has higher failure rates in young athletes. Surgery is done arthroscopically, usually after swelling has settled and motion has returned. Reconstruction is generally recommended for young, active people in pivoting sports and those with instability or a repairable meniscus tear, to protect the knee from further damage.

ACL injuries in children

Growth plates near the ACL are a concern in children and teens. Growth-plate-sparing reconstruction techniques are used, and delaying surgery while continuing to play increases meniscus and cartilage damage.

Recovery timeline after reconstruction

Returning before 9 months, or before passing strength tests, sharply raises the risk of re-injury.

Complications and outlook

• Re-tear of the graft or an ACL tear in the other knee, more common in young athletes returning to pivoting sports
• Knee stiffness or loss of motion
• Pain at the graft harvest site
• Higher long-term risk of knee osteoarthritis, with or without surgery, especially if the meniscus is damaged

Most people regain a stable knee and return to daily activities, and many return to sport.

Prevention

Neuromuscular training programs (such as FIFA 11+ and similar warm-ups) reduce ACL injuries significantly, especially in female athletes. They focus on landing with knees over toes, hip and core strength, balance and plyometrics, done 2 to 3 times a week as a warm-up.

Frequently asked questions

Can you walk with a torn ACL?

Often, yes. Once the initial swelling settles, many people can walk on flat ground with a torn ACL. The problem is instability when twisting, pivoting or changing direction, which can cause the knee to give way and damage the meniscus and cartilage.

How long does it take to recover from an ACL tear?

After reconstruction surgery, most people walk normally within a few weeks, run at 3 to 6 months and return to pivoting sports at 9 to 12 months. Without surgery, rehabilitation takes about 3 to 6 months to restore strength and function.

Does a torn ACL always need surgery?

No. People who are less active, avoid pivoting sports and do not have repeated giving way can do well with physical therapy alone. Surgery is usually recommended for young athletes, people with ongoing instability, and those with a repairable meniscus tear.

Can a partial ACL tear heal on its own?

Partial tears with a stable knee can do well with rehabilitation and may not need surgery. A complete tear does not heal back together in a way that restores stability. An MRI and examination help decide the best approach.

How do I know if I tore my ACL?

Classic signs are a pop at the time of injury, rapid swelling within hours, inability to continue playing, and later a knee that gives way when turning. Only an examination, such as the Lachman test, and an MRI can confirm the diagnosis.