Sex Differences in Knee Joint Laxity Change Across the Female Menstrual Cycle

1062 PURPOSE: To compare males and normal-menstruating females by analyzing serum hormone levels and anterior knee joint laxity for one month. METHODS: 22 females (23.0 ± 3.5 yrs, 163.4 ± 5.6cm, 65.0 ± 11.6 kg, 24.3 ± 3.5 BMI) were tested each morning (8:00a.m.-12:00N) across one complete menstrual cycle, and 20 males (23.3 ± 2.0 yrs, 181.5 ± 7.8 cm, 78.2 ± 11.1 kg, 23.7 ± 2.7 BMI) once per week (8:00–10:00a.m.) for four weeks. Serum levels of estradiol, progesterone and testosterone were assayed and knee laxity (displacement at 46, 90 P<.0001). For laxity across the three loads tested, females (daily means ranging from 3.6 ± 1.4 to 4.5 ± 1.5 mm) had greater displacement than the average value for males (3.0 ± 1.3 mm) on days M5, O3–5, EL1-4 and LL1,2,4,5. These data coincided with higher estradiol levels in females (daily mean range = 46 ± 19 – 175 ± 51 pg/mL) vs. males (55 ± 10 pg/mL) for the days near ovulation (O1–5) and luteal phases (EL1–5 & LL1-4), but not menses. Progesterone levels were also higher in females (daily mean range = 0.7 ± 0.3 – 12.7 ± 3.7 ng/mL) vs. males (0.8 ± 0.2 ng/mL) for days M1, O5, and all days of EL and LL. Within females, knee laxity was greater on day O5 compared to day M3, and days EL1-3 compared to all days of menses and day O1. CONCLUSIONS: These results suggest sex hormones may be a primary mediator of the observed sex differences in knee laxity. The consequence of increased knee laxity on neuromuscular and biomechanical function of the knee is currently being explored. Supported by NIH Grants RO3 AR47178 and MO1 RR00847, and through a ooperative agreement U54 HD28934 as part of the Specialize Cooperative Centers Program in Reproductive Research.