Variations in varus/valgus and internal/external rotational knee laxity and stiffness across the menstrual cycle.

Cyclic variations in genu recurvatum (GR), general joint laxity (GJL), varus-valgus (VV), and internal-external (IER) rotational laxities and stiffnesses were examined in 64 females and 43 males at two time points during the females' menstrual cycle [days of minimum (T1) and maximum (T2) anterior knee laxity (AKL)]. Cyclic increases in AKL (9.5%), GR (37.5%), and GJL (13.6%) were observed in females but not males from T1 to T2 (p < 0.001). Cyclic increases in VV and IER laxity were negligible (1.5-3.2%, p > 0.320). Females compared to males had lower overall VV stiffness at T2 (F 37% <M) vs. T1 (F 26.9% <M; p = 0.011), but no difference across time points for IER stiffness (p = 0.452). Across both time points, females had consistently greater VV (30.2%) and IER (20%) laxity and less VV (32.5%) and IER (24.3%) incremental stiffness (p < 0.001). Low-to-moderate associations were observed between AKL, GR, and GJL with VV and IER laxities and stiffnesses in females as measured at T1 and the change in values from T1 to T2. Whether these findings reflect ligament-specific responses to hormone changes, or implicate changes in injury risk potential across the menstrual cycle requires further study.