ACL Injuries in Sports

Anterior cruciate ligament injuries also known as ACL injuries are the most common injuries suffered by sports men and women today. It refers to a sprain or tear to one of the ligaments in the knee that join the upper leg bone together with the lower leg bone.

Athletes who participate in high demand sports like soccer, football, and basketball are more likely to injure their anterior cruciate ligaments.

If you have injured your anterior cruciate ligament, you may require surgery to regain full function of your knee. This will depend on several factors, such as the severity of your injury and your activity level.


Normal knee anatomy, front view

Three bones meet to form your knee joint: your thighbone (femur), shinbone (tibia), and kneecap (patella). Your kneecap sits in front of the joint to provide some protection.

Bones are connected to other bones by ligaments. There are four primary ligaments in your knee. They act like strong ropes to hold the bones together and keep your knee stable.

Collateral Ligaments

These are found on the sides of your knee. The medial collateral ligament is on the inside and the lateral collateral ligament is on the outside. They control the sideways motion of your knee and brace it against unusual movement.

Cruciate Ligaments

These are found inside your knee joint. They cross each other to form an “X” with the anterior cruciate ligament in front and the posterior cruciate ligament in back. The cruciate ligaments control the back and forth motion of your knee.

The anterior cruciate ligament runs diagonally in the middle of the knee. It prevents the tibia from sliding out in front of the femur, as well as provides rotational stability to the knee.

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ACL injuries are graded according to the extent of the tear. The ACL has lots of strong fibrous tissues that connect bones so that the knee is stable and therefore the ACL is considered to be one of the most vital ligaments in the human body.

ACL Tear Grading / Severity of ACL Sprain

ACL tear, sometimes referred to as a sprain, can be graded as I, II, III depending on its severity.

Grade 1 ACL Sprain

 In this type of sprain, the ACL is stretched, which may or may not include tearing of some of the fibers. Mild pain may be felt but the knee has minimal loss of stability. Grade 1 ACL sprain is sometimes called mild ACL sprain.

Grade 2 ACL Sprain

 There is considerable stretching of the ACL causing partial tearing of the ligament in grade 2 sprain, also called moderate ACL sprain. It can cause moderate pain, swelling and mild looseness in the knee joint.

Grade 3 ACL Sprain

 In grade 3 ACL sprain or severe sprain, the ACL is completely torn or ruptured. Symptoms are usually severe and the joint is unstable. Other structures of the knee may be damaged, as well.

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Research shows that women are six times more likely to suffer ACL injuries as compared to their male counterparts. It is also possible that genes play a role when it comes to ACL risk factors. These factors are divided into namely non-modifiable and modifiable.



–Female Gender

–Notch width

–Posterior tibial slope

–ACL size

–Ligamentous laxity


–High BMI

–Jump landing mechanics


–Playing surface

ACLI and Genetics

  • Many anecdotal reports of ACL injuries running in families
  • Two case-control studies support this theory

–Harner, AJSM 1994; Flynn, AJSM 2005

  • However, overall Evidence is poor, level III at best
  • Genetic studies exist, but few
  • Cannot make definitive conclusions or practice recommendations….yet

Several prospective level II evidence cohort studies have shown:

a)Females have smaller NWIs than males

b)Male and female athletes with ACLIs have significantly more notch stenosis than athletes without ACLIs

* Bony geometry of tibial plateau and ACLI

  • Both the concavity depth of the medial plateau and the degree of posterior-inferior tibial slope have been studied
  • Studies suggest that increased posterior tibial slope places athletes at higher risk for non-contact ACLIs

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