Influence Of Hormonal Contraceptive Use On Tibial Microarchitecture Adaptations To British Army Officer Training

Abstract

Hormonal contraceptives are commonly used by servicewomen. Hormonal contraceptives contain ethinyl oestradiol and progestogen, or progestogen only, and act by altering the endogenous production of 17β-Oestradiol. 17β-Oestradiol plays an important role in the mechanobiology of bone. PURPOSE: To investigate differences in tibial adaptations to 44-weeks British Army Officer basic training between women not using any hormonal contraceptive and women using the combined oral contraceptive pill (ethinyl oestradiol and progestogen: COCP) or a progestogen-only contraceptive (pill, subdermal implant, intramuscular injection: POC). METHODS: Scans of the tibial metaphysis (4% site) and diaphysis (30% site) were obtained using HRpQCT (XtremeCT II, Scanco, Switzerland) in 51 women during week 1, 14, 28, and 44 of training (non-users, n = 11; COCP users, n = 18; POC users, n = 17; other, n = 5; mean ± SD, age 24 ± 3 y, height 1.66 ± 0.06 m, body mass 64.3 ± 7.7 kg; p ≥ 0.079 between groups). Images were analysed for volumetric bone mineral density (vBMD), geometry, microarchitecture, and mechanical properties. RESULTS: Trabecular vBMD increased from week 1 to 44 at the 4% site (3.0%) and cortical vBMD decreased from week 1 to 14 at the 30% site (−0.3%) in all women (p < 0.001). Trabecular area decreased at the 4% site (−0.4%); trabecular volume (3.5%), cortical area (4.8%), and cortical thickness (4.0%) increased at the 4% site; and, cortical perimeter increased at the 30% site (0.5%) from week 1 to 44 in all women (p ≤ 0.005). Trabecular thickness increased in COCP users only (2.5%, p < 0.001), but trabecular spacing decreased in all women (−3.1%, p < 0.001) from week 1 to 44. Cortical porosity decreased from week 14 to week 28 in COCP users only (−14.3%, p = 0.030). Failure load at the 30% site decreased from week 1 to 44 in all women (2.5%, p < 0.001). There were no differences in vBMD, geometry, or mechanical properties, or trabecular number, trabecular spacing, or cortical pore diameter between hormonal contraceptive groups (p ≥ 0.161). CONCLUSIONS: Bone adapts to mechanical loading largely independently of hormonal contraceptive use, but POCs may inhibit adaptation of the trabecular microarchitecture in response to mechanical loading as a result of low endogenous and exogenous oestradiol.