Anterior cruciate ligament (ACL) injuries are among the most common and debilitating knee injuries in professional athletes with an incidence in females up to eight-times higher than their male counterparts. ACL injuries can be career-threatening and are associated with increased risk of developing knee osteoarthritis in future life. The increased risk of ACL injury in females has been attributed to various anatomical, developmental, neuromuscular, and hormonal factors. Anatomical and hormonal factors have been identified and investigated as significant contributors including osseous anatomy, ligament laxity, and hamstring muscular recruitment. Postural stability and impact absorption are associated with the stabilizing effort and stress on the ACL during sport activity, increasing the risk of noncontact pivot injury. Female patients have smaller diameter hamstring autografts than males, which may predispose to increased risk of re-rupture following ACL reconstruction and to an increased risk of chondral and meniscal injuries. The addition of an extra-articular tenodesis can reduce the risk of failure; therefore, it should routinely be considered in young elite athletes. Prevention programs target key aspects of training including plyometrics, strengthening, balance, endurance and stability, and neuromuscular training, reducing the risk of ACL injuries in female athletes by up to 90%. Sex disparities in access to training facilities may also play an important role in the risk of ACL injuries between males and females. Similarly, football boots, pitches quality, and football size and weight should be considered and tailored around females’ characteristics. Finally, high levels of personal and sport-related stress have been shown to increase the risk of ACL injury which may be related to alterations in attention and coordination, together with increased muscular tension, and compromise the return to sport after ACL injury. Further investigations are still necessary to better understand and address the risk factors involved in ACL injuries in female athletes.

Cite this article: Bone Jt Open 2024;5(2):94–100.

The anterior cruciate ligament (ACL) is frequently injured in elite athletes, with females up to eight times more likely to suffer an ACL tear than males. Biomechanical and hormonal factors have been thoroughly investigated; however, there remain unknown factors that need investigation. The mechanism of injury differs between males and females, and anatomical differences contribute significantly to the increased risk in females. Hormonal factors, both endogenous and exogenous, play a role in ACL laxity and may modify the risk of injury. However, data are still limited, and research involving oral contraceptives is potentially associated with methodological and ethical problems. Such characteristics can also influence the outcome after ACL reconstruction, with higher failure rates in females linked to a smaller diameter of the graft, especially in athletes aged < 21 years. The addition of a lateral extra-articular tenodesis can improve the outcomes after ACL reconstruction and reduce the risk of failure, and it should be routinely considered in young elite athletes. Sex-specific environmental differences can also contribute to the increased risk of injury, with more limited access to and availablility of advanced training facilities for female athletes. In addition, football kits are designed for male players, and increased attention should be focused on improving the quality of pitches, as female leagues usually play the day after male leagues. The kit, including boots, the length of studs, and the footballs themselves, should be tailored to the needs and body shapes of female athletes. Specific physiotherapy programmes and training protocols have yielded remarkable results in reducing the risk of injury, and these should be extended to school-age athletes. Finally, psychological factors should not be overlooked, with females’ greater fear of re-injury and lack of confidence in their knee compromising their return to sport after ACL injury. Both intrinsic and extrinsic factors should be recognized and addressed to optimize the training programmes which are designed to prevent injury, and improve our understanding of these injuries. Cite this article: Bone Joint J 2023;105-B(10):1033–1037

Introduction and Aims: Hormonal factors are one plausible explanation for differences in musculotendinous stiffness (MTS) and knee laxity between men and women, and the resulting higher risk for ACL injury in women. This study examined MTS and ACL laxity over the course of the menstrual cycle in women and investigated the interaction of warm-up. Method: Eight female netball players aged between 16–18 years (mean = 16.3 ± 0.8 years) participated in this study. None of the participants were using oral contraceptives and all demonstrated regular menstrual cycles. Venous blood samples and MTS data were collected each week over the 28-day menstrual cycle. MTS was assessed prior to, and following a standardised warm-up consisting of light cycling and jumping. ACL laxity was determined at the beginning of each test session using the KT2000™ knee arthrometer (MEDmetric Corporation, San Diego, USA). Results: Repeated measures ANOVA results revealed significant (p < 0.05) main effects of warm-up and test session on MTS. For the effect of warm-up, MTS was found to significantly decrease by 4.2% following the warm-up intervention, indicating that relatively low levels of activity can acutely alter the viscoelastic properties of muscle. Post hoc contrasts for test session revealed that MTS was significantly lower at week three (corresponding to the ovulatory phase), in contrast to weeks one and two (7% and 4.5% decrease, respectively). For ACL laxity, repeated measures ANOVA revealed no significant (p < 0.05) differences at 30 lb anterior force across the menstrual cycle. The results did however demonstrate a trend towards increased ACL laxity during ovulation (week three) when the lower limb musculature was most compliant. Conclusion: While there were no significant differences in static ACL laxity, reduced MTS is one of the main causes of prolonged electromechanical delay (EMD) and has particular relevance for ACL injury. In conclusion, females are at greater risk of incurring an ACL injury during ovulation when oestrogen levels are highest