Anterior cruciate ligament (ACL) tears are a common injury sustained by athletes. But why are females 2 to 10 times more likely to sustain an ACL injury, when compared to males playing the same sports?
what is the acl?
The ACL is a band of connective tissue which travels from the femur to the tibia. It primarily functions to resist the forwards translation and movement of the tibia (i.e. shin bone) in relation to the femur. In addition, it serves to limit rotational forces at the tibia. Both contact and non-contact injuries can occur, with non-contact injuries accounting for approximately 70% of all ACL tears. Common non-contact causes include a sudden change in direction or speed with the foot firmly planted, rapid deceleration from running with an attempt to change direction and/or landing from a height in or near full knee extension.
The increased risk of ACL injuries in females is believed to be due to gender specific differences in anatomy, hormonal effects, neuromuscular control, biomechanics and sport participation.
Differences in muscle activation patterns have been identified between males and females. Females have been observed landing with a “quad” dominant pattern, and with lesser degrees of hamstring muscle recruitment and activation, compared to their male counterparts. This results in increased tibial shear stresses and thus an increased risk of ACL injury. In addition, females have been identified as being less effective in “stiffening” their knee. Female athletes have therefore demonstrated greater degrees of tibial laxity compared to their male counterparts.
Regardless of gender, small femoral notches (i.e. the groove positioned at the base of the femur) are associated with an increased risk of ACL injury. Females have been found to have smaller and narrower femoral notches than males of the same weight and height thereby increasing their risk of an ACL injury.
More research is required to better understand the role of hormones on ACL injury risk. However, there is an increased likelihood of generalised ligamentous laxity in females.
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