Patient Education

To help you understand and navigate through your orthopedic health decisions, we have created a patient education section. Please select from one of the categories below to learn more about your condition or procedure.
Anterior Cruciate Ligament (ACL) Injuries

About Anterior Cruciate Ligament (ACL) Injuries

The anterior cruciate ligament (ACL) is an important internal stabilizer of the knee joint, restraining hyperextension. Anterior cruciate ligament injury occurs when the ligament is over-stretched, often with a hyperextension mechanism.

Formerly, ACL injuries occurred most often in a sports contact injury, when other structures were frequently involved. A particularly severe form of the contact injury is called the “unhappy triad” or “O’Donaghue’s triad“, and involves the anterior cruciate ligament (ACL), the medial collateral ligament (MCL), and the medial meniscus. Presently, ACL injury is more commonly a non-contact injury, such as a wrong landing from a layup in basketball. ACL injuries occur more frequently in athletes than in the general population and are prevalent in alpine skiing, football, soccer, basketball, rugby, wrestling, martial arts, and gymnastics. It is also known to be about three times more common in women than men.

The consequences of the injury depend on how much the stability of the knee is affected, and the extent to which other structures have been involved, and this can vary on a case-by-case basis. If instability is evident, particularly rotatory instability, then the menisci will get injured, sooner or later, setting the scene for progressive, degenerative, arthritis of the knee.

Common Symptoms

The main symptoms of an anterior cruciate ligament (ACL) injury include:

  • A loud pop or popping sensation in the knee at the time of injury
  • Severe pain and swelling in the knee within 24 hours
  • Instability or feeling like the knee may “give out”
  • Loss of full range of motion and difficulty walking
  • Tenderness along the joint line of the knee

Other potential symptoms include:

  • Inability to continue activity after the injury
  • Rapid swelling of the knee joint

The severity of symptoms can vary based on whether it is a complete or partial ACL tear. With a complete tear, the symptoms are usually more pronounced with significant instability and swelling.

Cause & Anatomy

ACL injuries commonly occur during sports activities that involve sudden stops, changes in direction (cutting), pivoting, jumping, and landing awkwardly. The ligament can tear due to:

  • Sudden deceleration and change of direction while running or pivoting with the foot planted
  • Landing awkwardly from a jump, causing excessive knee rotation or hyperextension
  • Direct blow to the knee, such as during a football tackle

Women are at higher risk of ACL injuries compared to men, potentially due to differences in anatomy, muscle strength, and hormonal factors. Other risk factors include poor conditioning, faulty movement patterns (e.g., inward knee movement during squats), and wearing inappropriate footwear.

When the ACL is stretched, partially torn, or completely torn, it can lead to knee instability, swelling, and pain, often accompanied by a “popping” sound at the time of injury. Prompt diagnosis and treatment are crucial to prevent further damage and restore knee stability and function.

The ACL is located in the center of the knee joint, running diagonally through the middle of the knee and connecting the posterior part of the femur to the anterior part of the tibia. It works together with the posterior cruciate ligament (PCL) to control the back-and-forth motion of the knee.


The diagnosis of an anterior cruciate ligament (ACL) injury typically involves the following steps:

Physical Examination

The doctor will perform a physical examination of the knee, which may include:

  • Checking for swelling, tenderness, and limited range of motion
  • Assessing knee stability by performing specific tests like the Lachman’s test, anterior drawer test, and pivot shift test
  • Evaluating for other associated injuries like meniscus tears or collateral ligament damage

Patient History

The doctor will ask about the mechanism of injury, such as a sudden twisting or pivoting motion, a direct blow to the knee, or a hyperextension injury. They will also inquire about the presence of a “popping” sound at the time of injury and the severity of pain and swelling.

Imaging Tests

X-rays may be ordered to rule out any fractures or bone injuries. However, the most valuable imaging test for diagnosing ACL tears is an MRI (magnetic resonance imaging) scan. MRI can clearly visualize the soft tissues, including the ACL, and determine the extent of the tear (partial or complete). In some cases, particularly in pediatric patients, a stress X-ray may be performed to assess knee instability and indirectly evaluate the ACL integrity.

Additional Tests

In rare cases, if the diagnosis remains unclear, the doctor may recommend an arthroscopic examination. This minimally invasive procedure involves inserting a small camera into the knee joint to directly visualize the ACL and other structures.

The combination of a thorough physical examination, patient history, and imaging tests (especially MRI) allows doctors to accurately diagnose ACL injuries and determine the appropriate treatment plan, which may involve conservative management or surgical reconstruction.


By implementing comprehensive, multicomponent neuromuscular training programs, especially in high-risk populations, ACL injury rates can potentially be reduced by up to 75%. Here are some key points on preventing anterior cruciate ligament (ACL) injuries:

Neuromuscular Training Programs

Multicomponent neuromuscular training programs that include a combination of strength, plyometric, agility, balance, and flexibility exercises are highly recommended for reducing ACL injury risk. These programs aim to improve movement biomechanics, muscle activation patterns, and neuromuscular control.

  • Specific exercises should focus on:
  • Proper landing and cutting techniques
  • Increasing core, hip, and leg strength
  • Enhancing balance and proprioception

Early Implementation

Implementing preventive training programs at a young age (before high injury risk) and continuing through competitive years is advantageous for optimizing motor learning and long-term retention of proper movement patterns.

Target High-Risk Groups

Female athletes in sports like basketball and soccer, as well as male football players, are at higher risk for ACL injuries and should be specifically targeted for preventive programs. Athletes with a previous ACL injury are also at elevated risk of re-injury and should perform preventive exercises to reduce this risk for both knees.

Training Frequency and Duration

For optimal benefits, preventive programs should be performed 2-3 times per week for 15-20 minutes per session, incorporated into pre-season and in-season training routines.

Proper Technique and Feedback

Providing feedback on proper exercise technique is crucial. Faulty movement patterns like excessive knee valgus, restricted hip/knee flexion, and poor landing mechanics increase ACL injury risk and should be corrected.


The treatment for an anterior cruciate ligament (ACL) injury depends on several factors, including the severity of the injury, the patient’s age, activity level, and associated injuries. The main treatment options are:

Non-surgical Treatment

Non-surgical treatment may be recommended for partial ACL tears or for individuals who are less active and have less demanding physical requirements. It typically involves:

  • Rest, ice, compression, and elevation (RICE) to reduce swelling and pain
  • Non-steroidal anti-inflammatory drugs (NSAIDs) for pain relief
  • Knee bracing or immobilization to protect the knee
  • Physical therapy to restore range of motion, strength, and stability

Non-surgical treatment aims to regain knee function without surgery, but it may not restore full stability, especially for active individuals or athletes.

Surgical Treatment

Surgical treatment, known as ACL reconstruction, is often recommended for complete ACL tears, especially in active individuals, athletes, and those with persistent knee instability despite non-surgical treatment. The surgery involves:

  • Arthroscopic reconstruction using a graft (tissue from the patient or a donor) to replace the torn ACL
  • Common graft options include autografts (patient’s own tissue, e.g., patellar tendon, hamstring tendon) or allografts (donor tissue)
  • Rehabilitation with physical therapy is crucial after surgery to regain strength, range of motion, and stability

The goal of ACL reconstruction surgery is to restore knee stability and function, allowing patients to return to their desired activity level, including sports.

Additional Considerations

  • Children and adolescents with open growth plates may require special surgical techniques to avoid disrupting growth
  • Associated injuries, such as meniscus tears or cartilage damage, may require additional treatment
  • Early diagnosis and treatment are important to prevent further knee damage and improve outcomes

The decision between non-surgical and surgical treatment depends on various factors and should be made in consultation with an orthopedic surgeon, considering the patient’s goals, activity level, and overall health.


Here are the key points about anterior cruciate ligament (ACL) injury surgery:

When is Surgery Recommended?

ACL surgery, also known as ACL reconstruction, is typically recommended in the following cases:

  • Complete ACL tears, especially in active individuals and athletes
  • Persistent knee instability despite non-surgical treatment
  • Associated injuries like meniscus tears that require surgical repair

Surgical Procedure

The surgery involves arthroscopic reconstruction of the torn ACL using a graft (tissue from the patient or a donor). Common graft options include:

  • Autografts (patient’s own tissue)

– Patellar tendon graft

– Hamstring tendon graft

  • Quadriceps tendon graft
  • Allografts (donor tissue from a tissue bank)

– The graft is secured into bone tunnels drilled in the femur and tibia to recreate the function of the torn ACL.

Surgical Considerations

  • Children and adolescents may require special surgical techniques to avoid disrupting growth plates.
  • Associated injuries like meniscus tears or cartilage damage may require additional treatment.
  • Early diagnosis and treatment are important to prevent further knee damage.


Rehabilitation with physical therapy is crucial after ACL surgery to regain strength, range of motion, and stability. The rehabilitation process typically takes 6-12 months before returning to sports or high-level activities. The decision to undergo ACL surgery depends on various factors, including the patient’s age, activity level, associated injuries, and goals. It should be made in consultation with an orthopedic surgeon, considering the potential risks and benefits.


What are the symptoms of an ACL injury?
Common symptoms include:

  • A “popping” sound or sensation in the knee at the time of injury
  • Severe pain and rapid swelling within 24 hours
  • Instability or feeling like the knee may “give out”
  • Limited range of motion and difficulty walking

How are ACL injuries diagnosed?
Diagnosis typically involves:

  • Physical examination (assessing knee stability, swelling, and range of motion)
  • Patient history (mechanism of injury, symptoms)
  • Imaging tests like X-rays (to rule out fractures) and MRI (to visualize soft tissue damage)
  • In some cases, arthroscopic examination may be performed for direct visualization.

Why does ACL recovery take so long?
Recovery is prolonged due to:

  • The knee’s complex anatomy and role in weight-bearing
  • Limited blood supply to the ACL, slowing healing
  • Need to regain full range of motion, strength, and stability through rehabilitation

Are females at higher risk?

Yes, studies show females are 2-7 times more likely to sustain ACL injuries compared to males in the same sports. Potential reasons include anatomical differences, muscle strength imbalances, and hormonal factors.

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