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Anterior cruciate ligament injury
Other Resources UpToDate PubMed

Anterior cruciate ligament injury

Contributors: Colin M. Robbins, Sandeep Mannava MD, PhD
Other Resources UpToDate PubMed


Causes / typical injury mechanism / pathophysiology: Anterior cruciate ligament (ACL) injuries typically occur during athletic activities. The mechanism of injury often involves a deceleration or acceleration force in combination with increased valgus load on the knee. The most common mechanism is a noncontact cutting injury.

Another cause of ACL injuries are knee dislocations in the setting of high-energy traumatic injuries. In these cases, careful attention should be taken to assess other ligamentous and possible neurovascular injuries to the knee joint.

Classic history and presentation: Active, younger patients will more commonly rupture their ACL. A common presentation includes a patient who reports hearing / feeling a "pop" at the time of injury during an athletic activity. Additionally, hemarthrosis will commonly be seen within 2 hours of the suspected injury.

  • Age – Mean age of incidence is 29 years (+/- 11 years), but this injury can occur across all ages. Peak incidence varies based on sex:
    • Male peak incidence – 19-25 years old
    • Female peak incidence – 14-18 years old
  • Sex / gender – Both sexes can be affected, with a higher rate seen in the female population.
Risk factors:
  • Noncontact and contact sports activities (eg, football, lacrosse, soccer, basketball).
  • Anatomical risk factors for youth include increased anterior pelvic tilt, increased femoral anteversion, narrow intercondylar notch, increased posterior tibial slope, and a small ACL.
  • Female sex hormones (estradiol).
  • A valgus knee (anatomic versus dynamic). In dynamic valgus, the combination of adduction of the hip and valgus moment on the knee upon landing results in increased strain on the ACL.
  • Neuromuscular activation patterns (quad dominant).
Grade / classification system:
  • Lachman grade 1 – 3-5 mm anterior translation of the tibia in relation to the femur
  • Lachman grade 2 – 5-10 mm anterior translation of the tibia in relation to the femur
  • Lachman grade 3 – greater than 10 mm anterior translation of the tibia in relation to the femur
  • Modifiers –
    • A: firm endpoint
    • B: no endpoint


S83.519A – Sprain of anterior cruciate ligament of unspecified knee, initial encounter

444470001 – Injury of anterior cruciate ligament

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Differential Diagnosis & Pitfalls

  • If the mechanism of injury is high energy with a knee dislocation, be very diligent in assessing multiligamentous knee injury and neurovascular compromise, as the popliteal neurovascular bundle lies directly posterior to the knee joint.
  • Delay in diagnosis with the patient continuing to participate in higher risk activities (eg, soccer, basketball) can result in irreparable damage to the meniscus and cartilage.

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Last Reviewed:03/24/2021
Last Updated:03/24/2021
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Anterior cruciate ligament injury
Copyright © 2023 VisualDx®. All rights reserved.