The relationship between menstrual cycle and anterior knee laxity: a systematic review

Background There is a significant difference in the degree of knee joint laxity between males and females. The menstrual cycle and its hormonal effects on the knee may be partly responsible for this difference. The purpose of this study is to synthesize all available literature on anterior knee laxity (AKL) during the menstrual cycle and investigate the relationship between menstrual cycle and anterior knee laxity. Methods We systematically searched PubMed, Embase, Cochrane Library, and Web of Science databases up to July 2024. Screen the literature based on inclusion and exclusion criteria and extract data. The quality of randomized and non-randomized trials was evaluated using the Cochrane Collaboration tool and the Newcastle Ottawa Scale, respectively. Results Among 25 included studies (743 participants), 16 demonstrated AKL variations across menstrual phases. AKL was lowest during the follicular phase (days 1 to 9), increased during ovulation (days 10 to 14), and peaked in the luteal phase (days 15 to 28). For example, under 89N and 133N loads, AKL during ovulation was significantly higher than in the early follicular phase (6.3 ± 1.6 mm vs. 4.2 ± 1.7 mm, P = 0.025; 8.5 ± 1.8 mm vs. 6.1 ± 2.1 mm, P = 0.018). Women with genu recurvatum exhibited more pronounced phase-dependent laxity. Progesterone (r = 0.70–0.76) and relaxin (r = 0.58–0.65) correlated strongly with AKL during the luteal phase, while estradiol’s role remained inconsistent. Conclusions Based on all the articles we have included, we speculate that AKL fluctuates across menstrual cycle phases, with the lowest laxity during the follicular phase. AKL progressively increases during ovulation and peaks in the luteal phase. Progesterone and relaxin are likely key mediators, while estradiol’s role warrants deeper exploration.