KNEE LAXITY BUT NOT ANTERIOR CRUCIATE LIGAMENT COMPLIANCE INCREASES ACROSS THE MENSTRUAL CYCLE

Abstract

PURPOSE To quantify and compare changes in knee displacement and anterior cruciate ligament behavior across the menstrual cycle as a function of fluctuating hormone levels. METHODS 20 females (not on oral contraceptives), with normal cycles of 28–32 days for the previous 6 months, were tested each morning across one complete menstrual cycle. 5cc of blood were drawn to assay estrogen and progesterone levels, and ligament compliance (89–134N) and knee displacement (134N) were assessed with a standard knee arthrometer. Data were aligned across all females at the onset of menses (M), the initial estrogen surge near ovulation (E2O), and the initial progesterone surge of early luteal phase (EL). The first five days of each phase were analyzed. RESULTS Estrogen levels (mean ± SD) for M, E20 and EL respectively were 53 ± 2, 134 ± 7, and 110 ± 5pg/mL, and progesterone levels were 0.92 ± .08, 0.87 ± .04 and 7.0 ± .51ng/mL. Displacement differed by phase (P = .007) and days within phase (P = .033). Displacement was greater at EL (5.5 ± 0.4mm) compared to M (4.9 ± 0.4mm) and E2O (5.1 ± 0.4mm). While there was no difference across days for M or E2O, displacement was .5–.7mm greater at days 1–3 of EL compared to days 4 and 5. Days 1–3 of EL were also generally greater (range = 0.6–1.0mm) than days of M, and early days of E2O. We found no difference in ACL compliance across phase (P = .775) or phase by day (P = .254). CONCLUSIONS Based on the 15 days examined, our findings suggest anterior knee laxity (but not ligament compliance) increases following the initial estrogen surge as progesterone begins to rise, then begins to decrease as progesterone continues to rise. Ongoing work is exploring the specific relationship between relevant hormones and their interactions, with changes in ligament behavior across the cycle. Supported by NIH Grants RO3 AR47178 and MO1 RR00847