Which risk factors are likely to account for the sex differences in non-contact anterior cruciate ligament injury rates?

Jane Grayson (2010). Which risk factors are likely to account for the sex differences in non-contact anterior cruciate ligament injury rates? PhD Thesis, School of Human Movement Studies, The University of Queensland.

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Author Jane Grayson
Thesis Title Which risk factors are likely to account for the sex differences in non-contact anterior cruciate ligament injury rates?
School, Centre or Institute School of Human Movement Studies
Institution The University of Queensland
Publication date 2010-04
Thesis type PhD Thesis
Supervisor Dr Robin Burgess-Limerick
Total pages 165
Total colour pages 18
Total black and white pages 147
Subjects 11 Medical and Health Sciences
Abstract/Summary Female athletes are known to have a higher rate of ACL injuries than male athletes in similar sports. Anatomical, neuromuscular, and strength factors have all been proposed as potential causes of this difference. The purpose of this investigation was to determine, through a series of three studies, the magnitude of sex differences, which exist in these potential risk factors. The first study investigated sex differences in anatomical risk factors. Male and female athletes from the Queensland Academy of Sport (Basketball: M = 14; F = 16; Soccer: F = 14) as well as the Men’s Lions Soccer club (n = 10) were recruited to participate in the study. A physical examination was completed which included: anthropometric measurements; lower extremity alignment measurements such as Q-Angle, knee recurvatum, and foot pronation; knee ligamentous laxity and muscle flexibility measurements; intercondylar notch width measurements using MRI; and an orthopedic examination. Our investigation found that anatomical differences do exist between healthy uninjured male and females. Females had larger Q-Angles, excessive foot pronation, decreased intercondylar notch width and increased ligamentous laxity and muscular flexibility compared to males. However, when examining the likely magnitude of these difference between the sexes, only a moderate effect was found (0.60 < ES ≤ 1.2). The second study investigated sex differences in strength measures that included knee flexion and extension peak torque values as measured using an isokinetic dynamometer, thigh muscle volume and cross sectional area (CSA) determined by Magnetic Resonance Imaging (MRI), and single leg hop for distance. Male and female athletes were recruited from the Queensland Academy of Sport (QAS) basketball program (M= 13; F = 13). Males were found to be significantly stronger than females even when all strength measurements were normalized to account for sex differences in anthropometrics (p < 0.05). Males generated greater peak forces in their knee extensors and flexors, greater hop distances and had larger muscle volumes and maximal cross sectional areas as determined by MRI analysis. When examining the likely magnitude of these difference between the sexes, a moderate to large effect was found (1.00 < ES ≤ 2.8). The final study investigated sex differences in lower limb neuromuscular factors, viz: body-segmental motions; ground reaction forces; and muscle timing and recruitment patterns in response to a drop-landing task in a laboratory setting. Participants recruited for the study were male and female university students (M= 11, F = 11), currently attending the University of Queensland. Participants performed a drop-landing task that consisted of performing a total of eight vertical drop landings from a box, 40cm in height, onto a force platform. Lower extremity sagittal plane marker kinetics and kinematics for the hip, knee and ankle were collected to determine joint angles at impact of landing and then maximum angle reached, ROM from initial ground contact to maximum angle as well as joint angular velocities. Thigh muscle activation patterns (i.e. recruitment order) in response to the drop-landing task were also collected. Results found that the female group landed with decreased knee flexion angles and higher ground reaction forces per body weight during the impact of landing compared to the males. After initial impact, the females also reached the greatest angles at the hip and knee therefore producing the greatest ROM at these joints. In regards to thigh muscle activation patterns, both male and female groups activated the hamstring muscles, prior to quadriceps activation, a result that was not expected. In conclusion, several anatomical, neuromuscular and strength differences exist between male and female athletes with the greatest differences observed in the kinematic and strength data. Females could potentially best benefit from training programs that include strength and proprioception components as well as technique awareness in an attempt to reduce the current ACL incidence rates observed in female athletes.
Keyword anterior cruciate ligament, gender, female, risk factors, non-contact, mechanisms, anatomical, hormonal, neuromuscular
Additional Notes Page numbers 30,32-34,58-61,63-66,86,91-92,94-96 of thesis

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