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The Complete Guide to ACL Injuries


There are approximately 200,000 anterior cruciate ligament (ACL) injuries every year and between 80,000 to 100,000 involve partial or complete ligament tears. Yet more than half of them are self-inflicted. They involve no contact with another competitor, and they occur in a disproportionate number of female athletes—a problem that still persists though several new training programs have shown success in reducing the risk of injury.

akeg / flickr

Ligaments are structures made of tough, fibrous material that connect bones at joints. Of the four major ligaments that hold the knee joint in place, two of them—the anterior cruciate ligament (ACL) and the medial collateral ligament (MCL)—are the ones most susceptible to stretches, partial tears and complete ruptures. The ACL, which is positioned in the front (anterior) part of the knee, is the smallest of the four knee ligaments, and is especially important for stabilizing the knee during sports activities. When it tears, recovery can be expensive, challenging, and time-consuming.

How ACL Injuries Happen

The ACL prevents the shin bone (tibia) below from sliding underneath the thighbone (femur) above. Without ligaments, the knee would be unstable and susceptible to frequent dislocation. The ACL can be stretched, torn, or completely severed when an athlete runs, decelerates, stops quickly, lands awkwardly after a jump, hyper-extends the knee, is off balance, or changes direction with the knee in a straight (extended) position. The exact cause is not clear, but it probably involves the way muscles function or fail to function, and each person’s anatomy. When an athlete does not have adequate muscle strength, coordination, or balance to quickly react to the demands of sports, there is an increased risk for a serious knee injury. Often times, glute weakness and instability lead to excessive strain being placed on the ACL, says Steve Smith, an Athletes' Performance physical therapist.

Female Athletes and ACL Injuries

One of the reasons why girls and women have higher rates of ACL injuries is because the angle from their pelvis to their knees to their feet is different from their male counterparts, says Joshua Hackel, MD, Director of Primary Care Sports Medicine, Andrews Institute, Gulf Breeze, Florida. "The angle creates increased stress on the ACL, which can lead to an injury," he says. But the risk of that injury can be reduced by a training program that develops hamstring strength and flexibility, pelvic strength and flexibility, and core stabilization. There is no age limit as to when these training programs should begin, Hackel says (and this applies to boys as well as girls). "As long as they are not maxing out on the amount of weight being lifted and as long as they are being supervised by an adult who is knowledgeable about proper technique, we think resistance training is a good thing for adolescents.”

ACL Injuries by the Numbers

Estimated percentage of ACL injuries that occur during the planting and cutting movements used in all sports

Girls and women sustain ACL injuries 4 to 10 times more frequently than boys and men in the same sports.

Who’s At Risk of ACL Injuries

ACL injuries occur up to ten times more frequently in girls and women than in boys and men, and are most common in women. Various theories exist, including a lack of balanced muscle strength between the quadriceps and hamstrings and inappropriate training for specific sports movements such as landing after a jump, stopping suddenly, or quickly changing directions.

Basketball and soccer players are at the top of the high-risk group, but volleyball players, gymnastics, cheerleaders, hockey players, wrestlers, rugby players, lacrosse players and skiers are not far behind. Football players suffer ACL damage in non-contact movements, as well as when they sustain blows to the knee.


  • Severe knee pain at the moment of the injury and more pain when you try to stand
  • A loud popping sound at the moment of the injury
  • Swelling that develops within 12 hours
  • Inability to bear weight—a feeling that your knee will “give way”
  • Arthritis (later in life)
  • Instability immediately after the injury, as well as later in life

Initial Treatment

  • Apply ice 15 to 20 minutes at a time, at least 3-4 times a day to control swelling.
  • Elevate the leg/knee above the level of the heart to minimize swelling.
  • Do not move the knee. Use a splint, elastic wrap, or crutches.
  • Use a pain reliever such as ibuprofen.
  • Do not try to “walk it off.” Those who do risk further injury to the joint.
  • If you think it is a serious knee injury, such as a torn ACL, see a doctor as soon as possible.

Comeback Strategy

The time needed to return to full sports competition ranges from six to nine months. Here are some things you can do to bridge the gap between your rehab and return to your sport:

Movement Prep

  1. Mini Band Walking - Forward, Bent Knees
  2. Mini Band Walking - Lateral, Bent Knees
  3. Mini Band Walking - Forward, Straight Leg
  4. Mini Band Walking - Lateral, Straight Leg
  5. World’s Greatest Stretch (to challenge trunk and hip muscles)
  6. Drop Lunges (to challenge trunk and hip muscles)
  7. Straight Leg March
  8. Bent Knee March - Linear and Lateral
  9. Straight Leg Skip
  10. Bent Knee Skipping
  11. Cariocas

Strength and Stability

  1. Quadruped Posterior Rocking
    Why it works: maintains hip mobility while focusing on a neutral, stable trunk position
  2. Pillar Bridge - Front
    Why it works: improves pillar strength
  3. Pillar Bridge - Lateral
    Why it works: improves pillar strength
  4. Glute Bridge
    Why it works: improves glute strength
  5. 1/2 Kneeling Chops
  6. 1/2 Kneeling Lifts
    Why it works: activates the gluteals and trunk stabilizers in a static position very similar to lunging
  7. Deep Squat and Lunge Progressions
    Why it works: improves balance and gets all of your muscles and joints working together

Ease Pain with a Foam Roll

Work out kinks in your muscles, ease pain, and recover faster with a foam roll. Order here.

How to Avoid ACL Injuries

  • Allow more warm-up time in cold weather.
  • Do not increase exercise intensity, duration, or frequency more than 10 percent a week.


Incorporate these prehab exercises into your warm-up routine:

  1. Foam Roll - Gluteus Maximus
  2. Foam Roll - Gluteus Medius
  3. Foam Roll - IT Band
  4. Dorsiflexion Stretch - Half Kneeling
  5. Sidelying Hip Abduction/External Rotation
  6. Glute Bridge
  7. Glute Bridge - Marching

Movement Prep

Incorporate these exercises into your movement prep:

  1. Mini Band Walks
  2. Inverted Hamstring - In Place
  3. Inverted Hamstring - Moving
  4. Lunge Stretch - In Place
  5. Lunge Stretch - Moving

ACL Injuries and American Football

A study of elite-level running backs and wide receivers with ACL reconstructions showed that these athletes generally returned to their first game at 9 to 12 months following surgery. “Returning to football” is the point at which an athlete is ready to return to individual team practice. In a study published in the Journal of Orthopaedic & Sports Physical Therapy and authored by Mark Verstegen, Sue Falsone, Steve Smith and Russell Orr of Athletes’ Performance, the authors note: “Based on clinical experience, we feel that this milestone should be met 1 to 2 months prior to the athlete’s return to a competitive game. This means that rehabilitation efforts need to focus on returning players to practice and not just to the point of being able to performance train.”

“To determine if an athlete is ready to return to any movement-based sport, especially one that is a chaotic and involves violent collisions, the criteria or tests that are used should replicate the conditions as closely as possible. The criteria used to assess readiness should include position-specific, random movements that allow for bilateral comparison. Movement-based testing should be done with the athlete in a stressed or fatigued state. Because fatigue adversely affects motor control, it is important to see these potential problems in a controlled environment before placing the athlete back into such conditions under more random circumstances. Giving special consideration to fatigue is supported by the data from Bradley and colleagues, who reported that the majority of ACL injuries in the NFL that happened during games occurred later in the game.”

How to Reduce the Risk of Further Injury

Because a history of previous injury is the biggest risk factor for future injury, American football players who have undergone ACL reconstruction are more likely to be injured in the future. In the study mentioned earlier, the authors make several recommendations to reduce the risk of re-injury. “To lessen the risk, a high level of movement competency must be maintained through all stages of rehabilitation. Athletes must maintain a stable and mobile platform from which to move (a high level of pillar strength), so that excessive external forces inherent to the game do not unexpectedly create macrotrauma or even repetitive chronic microtrauma. One area that can easily influences is the athlete’s warm-up for both training and competition. We recommend that the warm-up be dynamic, weight bearing, proprioceptively rich, activate key stabilizers, and actively elongate/stretch the myofascial system.” This dynamic warm-up, or what we call Movement Prep, should be performed before every training session, practice, and game. Click here to see an example.


 Jim Brown, Ph.D. has written 14 books on health, medicine, and sports. His articles have appeared in the Washington Post, New York Post, Sports Illustrated for Women and Better Homes & Gardens. He also writes for the Duke School of Medicine, UCLA School of Medicine, Cleveland Clinic and Steadman-Hawkins Research Foundation.

Tags: Knee, Women, Football, Injury Prevention, Regeneration, Hockey, Injury, Prehab, Skiing, Soccer, Basketball, Rehabilitation, Field Hockey


  1. Joshua Hackel, MD, Director, Primary Care Sports Medicine, The Andrews Institute, Gulf Breeze, Florida
  2. Steve Smith, PT, DPT, SCS, CSCS, Manager, Performance Physical Therapy Services, Athletes’ Performance, Gulf Breeze, Florida
  3. Health Extra Newsletter, The Cleveland Clinic
  4. Sportsmetrics USA
  5. "Understanding and Preventing Noncontact ACL Injuries" (American Orthopaedic Society for Sports Medicine
  6. “Suggestions From the Field for Return to Sports Participation Following Anerior Cruciate Ligament Reconstruction: American Football” (Journal of Orthopaedic & Sports Physical Therapy)