The female ACL: why is it more prone to injury?
Section snippets
Contributing factors
Noncontact ACL injuries are multifactorial. It is helpful to think of these factors in different categories: intrinsic (not changeable), extrinsic (changeable), and combination (both) (Table 1). There are multiple factors involved. Intrinsic factors include alignment, hyperextension, physiologic rotatory laxity, ACL size, femoral notch size and shape, hormonal influences, inherited skills, and coordination. Extrinsic factors include strength, conditioning, shoes, and motivation. Combined
Consensus statement
A consensus conference was held in Hunt Valley, Maryland, on June 10, 1999, sponsored by the American Orthopaedic Society for Sports Medicine (AOSSM), National Athletic Trainers' Association (NATA), National Collegiate Athletic Association (NCAA), and Orthopedic Research and Education Foundation (OREF). The goal of the conference was to discuss anatomic, environmental, hormonal, and biomechanical risk factors for noncontact ACL injuries; specifically, what we know from the written information,
Hormonal
Sex hormones have effects on numerous end organs, as evidenced by changes during menarche and menopause. Estrogen, progesterone, relaxin, and other sex hormones have cyclic effects. There is no consensus of the scientific community that sex hormones play a role in the increased incidence of ACL injury in female athletes [11]. One must understand the hormonal activities during the cycle and the hormonal effects during the cycle [12] (Fig. 8). The cycle number begins with menses. The follicular
Anatomic differences
The lower extremity static alignment and measurements have not been predictive of ACL injuries [11], [20]. Authors frequently state that the female has a wider pelvis than the male. However, females have a narrower pelvis.
Horton and Hall, in 50 males and 50 females, all asymptomatic, found that males had a greater hip width by 3 cm and longer femoral length by 5 cm [21]. The ratios of hip width to femoral length were about equal—0.73 in males and 0.77 in females. Ratios appear to be a more
Femoral notch
The ACL size and orientation determine width and shape of the femoral notch. Regardless of gender, smaller notches have been associated with increased rate of ACL injury. Most authors report a smaller ligament is housed in a smaller notch. However, Muneta et al used measurements from 16 Japanese knee cadavers to determine ACL cross-sectional area as it relates to notch dimensions [36]. The small notch knees did not have a thinner ACL in them.
Anderson et al evaluated 100 high school basketball
Neuromuscular
Gender differences in neuromuscular activation patterns have been reported to contribute to ACL injury. Compared to males, females have been found to be less effective in stiffening their knee [47]. Maximum contraction of the knee musculature significantly decreased the anterior tibial translation in men and women comparing relaxed to contracted states. However, the percent increase in knee stiffness was significantly greater at the p = 0.003 level, with male percentages of 473% and females
Core stability
It has long been understood that lack of control contributes to an individual getting into a position that allows for an ACL rupture. In recent years, the realization of proximal control dictating distal function has become increasingly apparent. One concept that has been closely linked to this has been the idea of “core stability.” The “core” may be operationally defined as the abdominal, back extensor, and hip musculature strength/function that contribute to stability of the lumbopelvic–hip
ACL research retreat consensus statement
An ACL research retreat for gender bias was held in April 2001, with participants presenting their research in areas of neuromuscular, biomechanical, hormonal, and structural. Publication of this was done, and a consensus statement of what we know, what is still unknown, and where do we need to go was published in Clinical Biomechanics [64]. Multicenter prospective studies to look at the multiple factors contributing to the future in the biomechanical area is to develop more valid methods of
Prevention programs
Prevention programs emphasize a safe flexed, hip over knee over ankle landing pattern. Prevention programs have been implemented and have reduced injuries in athletes. From Chuck Henning in the 1980s, who implemented basketball players doing rounded turns and several step stops [65] to the ski slope where an understanding of the way to fall and control ski tips (Johnson), prevention is indeed possible [66], [67], [68], [69]. A prevention program and risk factor book is available [10].
Hewett et
Summary
Multiple factors are responsible for ACL tears. The key factor in the gender discrepancy appears to be dynamic, not static, and proximal, not distal. The factors involved in evaluating the female ACL are multiple. However, it is the dynamic movement patterns of hip and knee position with increased flexion and a coordinated proximal muscle firing pattern to keep the body in a safe landing position that are the most critical factors. An ACL injury at an early age is a life-changing event. We can
Acknowledgements
Thanks to John Willson, PT, and Carolyn Large, transcriptionist.
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