(M-485) Evaluating the effect of estrogen on ACL elasticity in females

Thursday, October 12, 2023

9:30 AM – 10:30 AM PDT

Location: Exhibit Hall - Row M - Poster # 485

Presenting Author(s)

AZ

Aya Zaatreh (she/her/hers)

Undergraduate Student
Stevens Institute of Technology
East Brunswick, New Jersey, United States

Primary Investigator(s)

SS

Sally F. Shady (she/her/hers)

Teaching Associate Professor and Associate Chair of Undergraduate Studies
Stevens Institute of Technology
Hoboken, New Jersey, United States

Introduction:: On average, there are 100,000 to 200,000 anterior cruciate ligament (ACL) sprains and tears in the United States each year, where females are up to an eight times greater risk of injury than males of the same age2,5. However, studies have largely been done comparing the anatomy of female and male athletes, attributing the higher rate of injury to the smaller stature of the female body without considering physiological factors as a potential cause. Within the literature, there is ambiguous information regarding the effect of biological factors to the higher rate of injury in females. This study aims to quantify the effect estrogen has on ACL elasticity during each phase of the menstrual cycle through analyzing the effect higher estrogen levels have on performance of ligaments in the female body.

Materials and Methods::

A primary analysis was conducted to determine the elastic strength of the ACL following the fluctuations of a 28 day menstrual cycle (Figure 1). Utilizing Hooke’s Law, values for Young’s Modulus of Elasticity were calculated for both studies for each phase of the menstrual cycle in order to validate that elasticity is a function with time. Following this validation, calculations were performed to quantify the stiffness of the ACL during each phase of the menstrual cycle as a function of force applied to the ligament. Finally, a Tukey test (n = 65) was performed to corroborate the results obtained between the two data sets. A p value of less than 0.05 suggests that the results from the two models are comparable. A detailed literature review was performed in order to obtain data regarding the anthropometric properties of the female ACL used throughout the calculations in the study. The length used throughout the study was 28.1mm and the cross sectional area was 39mm2,1. The data regarding ligament laxity, which is analogous to the maximum displacement of the ligament, was collected from Heitz et al. and Karageanes et al. for a comparative analysis.

Results, Conclusions, and Discussions::

Female ACL strength was quantified under various loading forces obtaining functions of elasticity (Table 1). The equations collected model the elasticity of the ACL during each phase of the menstrual cycle due to the fluctuations in laxity modeled within the literature. Through a comparison of the equations generated from the contrasting papers, the follicular phase exhibits the highest elastic properties validating that when estrogen concentration is lowest, ligament strength is highest. Following this analysis, the Tukey test yielded statistical significance of p < 0.01 for left knee data from Karageanes et al. with Heitz et al. from all phases. The Tukey test corroborates the evidence from each study, validating the hypothesis that estrogen levels do have an effect on ligament strength because both datasets support this conclusion.

Final equations were gathered regarding ligament strength as a function of force (Table 3). These equations verify that estrogen does have an effect on ligament strength in females. This analysis provides a more accurate representation of the elasticity of the female ACL; ultimately, more accurate biomechanical analysis is attainable on the mechanism of ACL tears in females.

This study opens the conversation on hormone levels affecting the female body beyond preparation for pregnancy, closing the gap between the understanding of the female and male bodies, and also begins the discussion on more accurately quantifying and measuring this data. Women’s anatomical, physiological, and biomechanical properties are different, and through understanding these differences the rate of injury can be reduced and perhaps can enhance treatment. Data needs to be collected that is representative of the entire population, and this study shows the lack of data in this area. Further analysis needs to be conducted on progesterone fluctuations, as this analysis only verified that low estrogen levels increase the mechanical strength of the ligament.

Acknowledgements (Optional): :

References (Optional): :

Cone SG, Howe D, Fisher MB. Size and Shape of the Human Anterior Cruciate Ligament and the Impact of Sex and Skeletal Growth: A Systematic Review. JBJS Rev. 2019 Jun;7(6):e8. doi: 10.2106/JBJS.RVW.18.00145. PMID: 31246862; PMCID: PMC7771555.

Evans J, Nielson Jl. Anterior Cruciate Ligament Knee Injuries. [Updated 2022 May 5]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK499848/

Heitz, N. A., Eisenman, P. A., Beck, C. L., & Walker, J. A. (1999). Hormonal changes throughout the menstrual cycle and increased anterior cruciate ligament laxity in females. Journal of Athletic Training, 34(2), 144-9. Retrieved from https://ezproxy.stevens.edu/login?url=https://www.proquest.com/scholarly-journals/hormonal-changes-throughout-menstrual-cycle/docview/206646196/se-2

Karageanes, Steven J. DO; Blackburn, Kim MSEd, ATC*; Vangelos, Zenos A. DO. The Association of the Menstrual Cycle with the Laxity of the Anterior Cruciate Ligament in Adolescent Female Athletes. Clinical Journal of Sport Medicine 10(3):p 162-168, July 2000.

Parsons JL, Coen SE, Bekker SAnterior cruciate ligament injury: towards a gendered environmental approachBritish Journal of Sports Medicine 2021;55:984-990.