Absolute serum hormone levels predict the magnitude of change in anterior knee laxity across the menstrual cycle

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Abstract
This study aimed to determine whether absolute sex hormone concentrations predict the magnitude of knee joint laxity changes across the menstrual cycle. Twenty-two females (18-30 years, body mass index <or=30), who reported normal menstrual cycles for the previous 6 months were tested daily across one complete menstrual cycle for serum levels of estradiol (E=pg/mL), progesterone (P=ng/mL), and testosterone (T=ng/dL), and knee joint laxity (K(Lax)=mm displacement at 134N) measured with a standard knee arthrometer. The change in K(Lax) across the cycle (maximum-minimum), and minimum (early follicular) and peak (postovulatory) hormone concentrations were recorded for each subject. A stepwise linear regression determined if the minimum, peak, or absolute change in hormone concentrations would predict the magnitude of change in K(Lax) across the cycle. K(Lax) changed on average 3.2+/-1.1 mm across the menstrual cycle (range, 1.5-5.3 mm). Minimum levels of E (39.9+/-11.8 pg/mL) and P (0.61+/-0.27 ng/mL), coupled with peak concentrations of E (199.6+/-54.9 pg/mL) and T (22.5+/-10.5 ng/dL) explained 57.6% of the change in K(Lax) across the cycle. Greater absolute changes in K(Lax) were observed in response to peak E and T levels when minimum E concentrations were lower and minimum P concentrations were higher in the early follicular phase. The absolute minimum concentrations of E and P in the early follicular phase appear to be important factors in determining the sensitivity of the knee joint's response to changing hormone levels.