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Publication: The American Journal of Sports Medicine
Publication Date: 01-MAR-02
Format: Online - approximately 5832 words
Delivery: Immediate Online Access
Author: Wojtys, Edward M. ; Huston, Laura J. ; Boynton, Melbourne D. ; Spindler, Kurt P. ; Lindenfeld, Thomas N.
Article Excerpt
Female athletes at the high school and collegiate level in the United States are expected to suffer over 30,000 serious knee injuries per year. (15,26) In recreational sports, the number of injuries is even greater. (11) Unfortunately, the consequences of these injuries will last beyond the recreational, high school, or collegiate sports seasons, and for many athletes, the effects last for years to come. (9)
Why women are two to eight times more likely to sustain ACL tears, depending on the sport and the level of competition, continues to be a challenging question for clinical and basic science researchers. (1,2,13) Sex differences in anatomy, neuromuscular performance, and hormonal profile are active areas of investigation. With the ever-increasing levels of sports participation among women and the understandable desire of female athletes to remain physically active, it is imperative that answers to this problem be found.
Our previous work has suggested that more ACL tears occur during the ovulatory phase of the menstrual cycle than would be expected if the risk were the same for every phase. (22,39,40) Because the menstrual cycle, and hormone fluctuations associated with it, is one of the most important differences between male and female athletes, we further investigated the distribution of these injuries during the cycle using hormone metabolite measurements.
Our previous questionnaire study was limited by the ability of the participants to recall the phase of the cycle at the time of injury. (39) Although the participants were consistent in their responses, they could have been consistently inaccurate. To overcome this limitation, we measured estrogen, progesterone, and luteinizing hormone metabolites in the urine within 24 hours of injury and at the start of their next menstrual cycle in 65 women with acute ACL tears. Use of this protocol allowed accurate determination of the cycle phase in which the ACL injury occurred. Our study objective was to determine whether an association exists between the menstrual cycle phase and the distribution of ACL injuries in female athletes. Our hypothesis was that menstrual cycle phase affects the susceptibility of female athletes to ACL injury. Secondarily, we wanted to use hormone confirmation to determine whether the patient's recall of cycle day at the time of injury was accurate in assessing the actual phase. In essence, we wanted to determine whether self-reported menstrual cycle phase is as accurate as laboratory determinations.
MATERIALS AND METHODS
Description of the Menstrual Cycle and Its Corresponding Phases
The menstrual cycle has been divided into three to five subsections based on the corresponding state of the ovary. (28) The most common system separates the cycle into three main phases: follicular, ovulatory, and luteal. The follicular phase, which begins on the first day of menstruation and has a mean length of 9 days, is the most variable in length. During this time, 10 to 20 follicles start to develop in the ovary. During the last half of the follicular phase, the diameter of the largest follicle increases rapidly, while the remaining follicles become atretic. Coincident with the development of the largest follicle, the concentration of luteinizing hormone rises. A surge of luteinizing hormone begins 24 hours before ovulation. Associated with this surge is a sharp peak in estrogen output, which occurs before or coincident with the surge in gonadotropins. The ovulatory phase extends over a period of about 5 days. During the last phase, known as the luteal phase (day 15 to the end of the cycle), the follicle collapses and the corpus luteum is formed if pregnancy does not occur. This phase lasts approximately 14 days. A rise in progesterone is seen during the middle of this luteal phase. Consequently, the abrupt cessation of progesterone release determines the onset of menstruation.
There is considerable variation in menstrual cycle length, but the mean length is generally 28 days. However, cycle lengths ranging from 23 to 35 days may also be considered normal if there is uniformity in the menstrual cycle range over time. (28,38) In view of the varying lengths of normal regular menstrual cycles, a defining time point in the cycle for plotting reference data has been established in the literature. (28) The luteinizing hormone peak, which can be identified by serum or urine specimens, determines when ovulation occurs and also allows accurate identification of the follicular and luteal phases.
Sample Size Justification
Preliminary studies showed a 1.6 times greater than expected incidence of ACL injuries in the late follicular/ ovulatory phase of the menstrual cycle, (39) which represented a moderate effect. To achieve 80% power to detect an effect size of 0.40 with two degrees of freedom and an alpha of 0.05, we calculated a needed sample size of 60 subjects.
Subjects
Sixty-nine women who sustained acute noncontact ACL injuries were recruited for this study within the first 24 hours after injury over a 2-year period through local high schools, colleges, and surrounding areas of four test sites: University of Michigan, Vermont Orthopaedic Clinic, Vanderbilt University Medical Center, and Cincinnati Sportsmedicine and Orthopaedic Center. All participants (and their parents if subjects were younger than 18 years of age) in the study were briefed on the study, and informed consent for participation was obtained. The protocols were reviewed and approved by the Institutional Review Board for use on human subjects. The average age of these women was 28 [+ or -] 10 years (range, 15 to 46)....
NOTE: All illustrations and photos have been removed from this article.
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