S15 - Associations Between Sex Hormone Levels, Puberty Onset and ACL Morphology in the Growing Porcine Knee Joint

Introduction: : The incidence of anterior cruciate ligament (ACL) injuries is rising rapidly, with over 200,000 cases reported annually in the United States. Among the adolescent population, females are 3 to 4 times more likely than males to incur an ACL tear. Puberty represents a critical window during which physiological and hormonal changes may influence injury susceptibility. In females, the onset of puberty typically occurs between 10 and 14 years and includes events such as menarche and initiation of regular menstrual cycles. Importantly, early puberty onset shortens the time between menarche and attainment of cycle regularity by 3–4 times, suggesting greater early estrogen exposure. However, the relationship between the timing of puberty onset, early hormone exposure, and ACL development remains poorly understood. To address this gap, the current study aims to assess associations between the timing of puberty onset, levels of sex hormones, and ACL morphology.

Materials and

Methods: : For this study, six 4-month-old female Yucatan minipigs were longitudinally monitored from 4 months (pre-pubescent) to 10 months (mid-adolescence) of age. Throughout the study period, serum samples were collected, under sedation, weekly from each animal, with increased sampling frequency (three times per week) during the three weeks leading up to magnetic resonance imaging (MRI) and euthanasia. Body weight was recorded biweekly. Progesterone (P4) concentrations were quantified using a custom enzyme-linked immunosorbent assay (ELISA), while estradiol (E2) levels were measured via radioimmunoassay (RIA). T2* sequence MRI scans were performed at 10 months of age and were timed to occur seven days prior to the time of estrus. From MRI scans, the anterior cruciate ligament (ACL) was manually segmented to assess volumetric and cross-sectional area (CSA) metrics. Associations between puberty onset, levels of sex hormones and ACL morphology were assessed using a linear regression. Correlation strength was measured with R (range: -1 to 1), where |R| < 0.3 indicates no association, 0.3–0.5 weak, 0.5–0.7 moderate, and >0.7 strong.

Results, Conclusions, and Discussions:: In this study, the distinct onset of progesterone (P4) peaks allowed us to clearly identify when the pigs began puberty and to monitor their cycles throughout maturation. Progesterone peaks lasted longer than estrogen peaks, making them easier to detect. Progesterone levels remained below 0.2 ng/mL until the onset of puberty (Fig. 1A) and then peaked every ~3 weeks. Puberty onset, defined by the first progesterone peak, occurred at an average age of 6.6 ± .62 months (Fig. 1B). The timing of puberty onset was strongly and negatively associated with body weight at 10 months (R = –0.91; Fig. 2A). Notably, earlier puberty onset was associated with greater ACL size, as measured by both volume (R=-0.65) and CSA (R=-0.73) (Fig. 2B and 2C). Finally, moderate associations were observed between earlier puberty onset and lower final E2 (R=0.67; Fig. 2D) and greater final P4 peaks (R=-0.50, 2E).
This study demonstrates that earlier onset of puberty is associated with higher final body weight and larger ACL size. These findings align with existing literature indicating that girls who reach menarche earlier tend to have greater fat mass accumulation. Additionally, studies have shown that a smaller ACL size is associated with a higher risk of injury, and the current data suggest that timing of puberty may play a role on ACL size. Lastly, a mild association was observed between early onset of puberty and lower estrogen peaks alongside higher progesterone peaks. These associations may impact whether these hormones have a protective anabolic or detrimental catabolic effect on the ACL, as estrogen and progesterone are generally associated with catabolic changes and anabolic changes, respectively. In ongoing work, a larger set of animals as well as mechanical and compositional changes to the ACL will be assessed. This will allow for a comprehensive analysis on how the timing of puberty onset can impact ACL morphology and function.

Acknowledgements and/or References (Optional):: We would like to acknowledge the NC State College of Veterinary Medicine and Laboratory Animal Resources for their help.