Sex-dimorphic landing mechanics and their role within the noncontact ACL injury mechanism: evidence, limitations and directions

Injuries to the anterior cruciate ligament (ACL) continue to occur at an alarming rate, whilst carrying significant short- and long-term morbidity and an enormous financial burden [1,2]. Individuals having ruptured their ACL, for example, have a higher susceptibility to developing, within 10-15 years of injury, osteoarthritis at the knee joint [3,4]--a degenerative joint disease that most often leads to knee arthroplasty. An additional concern is the large sex-disparity in injury rates, with females suffering noncontact ACL injuries 2-5 times more frequently than males [5,6]. Given the potentially severe outcomes of this ligament injury, research efforts remain focused on elucidating its causes. A better understanding of its aetiology will allow for more effective risk screening and prevention methods to be developed, and thus a reduction in injury rate and its associated sex disparity.As a step toward more effective injury screening and prevention, the manoeuvres during which most ACL injuries occur have been identified and examined. Most non-contact ACL injuries are reported to arise from a sudden deceleration while either running and changing direction or landing from a jump [7]. Due to the difficult and unethical nature of deliberately provoking and analysing actual injury causing episodes, researchers have focused on obtaining joint neuromechanical data within systematic examinations of noninjurious scenarios. In particular, numerous research teams have compared the lower-limb mechanics of women performing landing tasks with those of men to gain insights into sex-dimorphic ACL injury rates [8-14]. Subsequently, those joint mechanical variables for which sex-based differences were revealed have been directly inferred as contributing risk factors for ACL injury and its associated sex-specificity. In spite of an extensive array of research with this specific intent, these variables have been inconsistently identified across studies. Such discrepancies make effecti