NASM Research Update Why Do Girls Sustain More Anterior Cruciate Ligament Injuries Than Boys? A Review of the Changes in Estrogen and Musculoskeletal Structure and Function during Puberty
Catherine Y. Wild, Julie R. Steele and Bridget J. Munro Sports Med 2012: 42 (9) 733-749.
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Introduction • Most child-related sports injuries occur during puberty corresponding to adolescent growth spurt. • Adolescent girls appear to be at 2x’s greater risk than boys for ACL injury, particularly in sports involving repetitive jumping and running – Prior to puberty girls and boys have similar injury rates
• Potential risk factors for ACL injury include – Hormonal (effects of estrogen on ACL) – Anatomical (knee laxity, lower limb strength and flexibility) – Biomechanics (altered landing mechanics on ACL)
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Purpose • The purpose of this review is to explain: 1. The effects of estrogen levels on the physiological properties of the ACL 2. Changes in musculoskeletal structure and function that occur during puberty (e.g., knee laxity, lower limb flexibility and strength) 3. Landing techniques displayed by pubescent girls
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Overview • An initial search in MEDLINE (1950+), CINAHL (1982-2011) and SPORTDiscus™ (1982-2011) in December 2011, limited to articles published in English, was conducted. • 41 total research papers were selected based on specific criteria
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Anthropometric and Hormonal Changes • Anthropometric Changes – A growth spurt causes a rapid increase in both length and mass of the lower limbs and may affect lower limb flexibility, strength, and performance – These rapid growth changes may contribute to the greater number of ACL injuries sustained by females during this time
• Hormonal Changes – For girls estrogen levels substantially rise at the onset of puberty – Hormonal differences between boys and girls may play a role in ACL injury
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Estrogen Levels • Fibroblasts are essential for repairing microscopic damage to ligaments • Estrogen may negatively affect fibroblasts ability to repair ligaments and the metabolic properties of the ACL • Therefore, increased levels of estrogen experienced by adolescent girls may affect the mechanical integrity of the ACL • More research is needed to confirm
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Musculoskeletal Changes • Lack of quadriceps strength may play a role in ACL injury – Lack of strength may be due to hormonal differences between adolescent boys and girls (testosterone vs. estrogen)
• Decreased hamstring strength compared to quadriceps strength may lead to ACL injury • Lack of overall strength may lead to knee instability particularly during knee jump landing tasks
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Lower Limb Landing Mechanics • Poor landing mechanics characterized by increased knee joint valgus (knees collapsing inward) is a common cause of ACL injury in pubescent girls
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Conclusions • Girls display a higher incidence of ACL injury compared to boys during puberty • Research suggests increased estrogen levels may play a role in ACL injury but more evidence is needed • Pubescent girls may not develop quadriceps and hamstring strength at the same rate as boys, which may lead to knee instability and ACL injury • Girls tend to display greater knee valgus, particularly during jump landing tasks, increasing the risk for ACL injury COPYRIGHT 2012, NATIONAL ACADEMY OF SPORTS MEDICINE