Document Title: Belanger-AJSM-Jul04
Article Title: Knee Laxity Does Not Vary With the Menstrual Cycle, Before or After Exercise
Authors: Michael J. Belanger, MD*, Douglas C. Moore, MS,, Joseph J. Crisco, PhD, III, Paul D. Fadale, MD, Michael J. Hulstyn, MD and Michael G. Ehrlich, MD
Publication: American Journal of Sports Medicine, Baltimore, Maryland
Date: July 2004
Volume 32, pages 1150-1157

(Figures included. Reference-denoting numbers appear in the same point size as the document text.)

Irrespective of how ligaments are influenced by the menstrual cycle, keep in mind that there are many factors behind female athletes having a manyfold higher ACL-injury rate than their male counterparts. For quantification of knee-ligament properties, this article used only anterior-drawer laxity, as measured by the Lachmann Drawer Test via the KT-2000 device. The problem is that such testing is not sophisticated enough to accurately measure strength of the ligament. The main reason is that such testing necessarily involves forces much lower than those which tear ligaments. So, it is entirely possible for the ACL in a female during the luteal (high-estrogen) phase to have a lower maximum tensile stress than that of the same person during the rest of the menstrual cycle. The authors compare their study results to studies done on animals. (With animals, the advantage is that it is relatively easy to find the tensile strength of ligaments: all that needs to be done is to sacrifice the animal and place the ligament-and-bone assembly in a tensile-testing machine.) This study is, in many ways, similar to the one by Van Lunen, which can also be found here in the Knee Library. Belanger et al did find very small differences in knee laxity throughout the menstrual cycle, but the variation did not correlate unequivocally to any certain part of the menstrual phase. It must also be kept in mind that KT-2000 measurements are not really fraction-of-a-millimetre-precise anyway. Results are affected by the technique of the examiner (and in fact, whether the examiner is right-handed or left-handed makes a difference too, as Van Lunen also noted), and will naturally vary slightly over time (and so, taking KT-2000 measurements of a male athlete, over the course of a month, will probably also show a variation of about a millimetre or so). The real value of KT-2000 measurements lies in their comparative ability: that is, when examining an ACL-injured knee, it is necessary to compare the laxity in that knee to the laxity in the other knee, which is presumed to be uninjured. (Typically, only the difference in laxity is recorded.)

Background: An intriguing explanation for the disproportionately high rate of anterior cruciate ligament injury in female athletes is that the structural properties of the anterior cruciate ligament are affected by the menstrual hormones. Whether this actually occurs, however, is the subject of ongoing debate.

Hypotheses: (1) Anterior cruciate ligament laxity is different in the follicular, ovulatory, and luteal phases of the menstrual cycle, and (2) exercise exacerbates the difference in anterior cruciate ligament laxity in the 3 phases.

Methods: Over the course of 10 weeks, repeated knee laxity measurements were taken on 27 high-level female athletes, before and after exercise. Point in the menstrual cycle was determined with charts of waking temperature and menstruation. The independent effects of menstrual phase and exercise were evaluated using generalized estimating equations.

Results: Data from 18 participants were included in the final analysis. There were no significant differences in anterior cruciate ligament laxity in any of the 3 menstrual phases, before or after exercise.

Conclusions: Anterior cruciate ligament laxity is not significantly different during the follicular, ovulatory, and luteal phases of the menstrual cycle, and bicycling exercise does not exacerbate or create any differences in anterior cruciate ligament laxity.

Key Words: anterior cruciate ligament, menstrual cycle, knee laxity, KT-series arthrometer

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