Blogs from February, 2023

holding knee

Risk Factors

Research has shown that there are several risk factors for sustaining an ACL injury. Some of these risk factors are related to the anatomy of the knee joint and considered non-modifiable.

  • There is a space in the knee joint called the intercondylar notch. A smaller intercondylar notch is associated with higher risk for ACL injury.
  • The size of the ACL. Smaller ACL (cross-sectional area and volume) is associated with higher risk for ACL injury.
  • Laxity of the knee. Some people’s ligaments are naturally a little more “loose” than others. This laxity is associated with higher risk for ACL injury.
  • Research is ongoing but hormone fluctuations change the mechanical properties of the ligament. The risk of sustaining an ACL injury is greater during the preovulatory phase of the menstrual cycle in females.

Other risk factors are related to neuromuscular control and are considered modifiable or trainable.

  • Dynamic knee valgus – the ACL is loaded more when the knee falls in and is rotated in.
  • Hip muscle weakness – weakness of the muscles around the hip often lead to dynamic knee valgus movement patterns where the knee falls in and is rotated in
  • More erect posture when landing from a jump – there are increased forces when landing from a jump with less knee bending. This is a faulty pattern of movement, but it may also be related to hip muscle weakness.
  • More quadriceps activity – the quadriceps muscle creates more forward shear of the lower bone of the knee on the top bone. When landing from a jump in a more erect posture, the quadriceps are activated more, creating this greater shear and stress on the ACL.

Because approximately 80% of ACL injuries are non-contact, it seems possible to reduce the incidence of these injuries. The focus of these ACL prevention programs is in reducing these modifiable risk factors through training programs. ACL part 3 will focus on the research on prevention programs.


Brotzman SB, Manske R. Clinical Orthopaedic Rehabilitation: An Evidence Based Approach. 2011 Mosby

Shultz SJ, Schmitz RJ, Benjaminse A, Chaudhari AM, Collins M, Padua DA. ACL research retreat VI: An update on ACL injury risk and prevention. J Athl Train 2012; 47(5):591-603.

Wilk KE. Anterior cruciate ligament injury prevention and rehabilitation: Let’s get it right. J Orthop Sports Phys Ther 2015; 45(10) 729-30.