Fracture incidence in relation to the pattern of use of hormone therapy in postmenopausal women

Context: Evidence is limited on the effects of different patterns of use of postmenopausal hormone therapy on fracture incidence and particularly on the effects of ceasing use. Objective: To investigate the effect of different patterns of hormone therapy use on fracture incidence. Design, Setting, and Participants: Prospective study of 138737 postmenopausal women aged 50 to 69 years recruited from the UK general population in 19961998 (the Million Women Study) and followed up for 1.9 to 3.9 years (average, 2.8 years) for fracture incidence. Main Outcome Measure: Adjusted relative risk (RR) for incident fracture (except fracture of the fingers, toes, and ribs) in hormone therapy users compared with never users at baseline. Results: A total of 5197 women (3.7%) reported 1 or more fractures, 79% resulting from falls. Current users of hormone therapy at baseline had a significantly reduced incidence of fracture (RR, 0.62; 95% confidence interval [CI], 0.58-0.66; P<.001). This protection was evident soon after hormone therapy began, and the RR decreased with increasing duration of use (P=.001). Among current users at baseline the RR of fracture did not vary significantly according to whether estrogen-only, estrogen-progestin, or other types of hormones were used (RR [95% CI], 0.64 [0.58-0.71], 0.58 [0.53-0.64], and 0.67 [0.56-0.80], respectively; P=19), nor did it vary significantly according to estrogen dose or estrogen or progestin constituents. The RR associated with current use of hormone therapy did not vary significantly according to 11 personal characteristics of study participants, including their age at menopause, body mass index, and physical activity. Past users of hormone therapy at baseline experienced no significant protection against fractures (RR, 1.07; 95% CI, 0.99-1.15); incidence rates returned to those of never-users within about a year of ceasing use. Conclusions: All types of hormone therapy studied confer substantial protection against fracture while they are used. This protection appears rapidly after use commences and wears off rapidly after use ceases. The older women are, the greater is their absolute reduction in fracture incidence while using hormone therapy.

Mode I fracture of sheet metal

The perceived wisdom about thin sheet fracture is that (i) the crack propagates under mixed mode I & III giving rise to a slant through-thickness fracture profile and (ii) the fracture toughness remains constant at low thickness and eventually decreases with increasing thickness. In the present study, fracture tests performed on thin DENT plates of various thicknesses made of stainless steel, mild steel, 6082-O and NS4 aluminium alloys, brass, bronze, lead, and zinc systematically exhibit (i) mode I “bath-tub”, i.e. “cup & cup”, fracture profiles with limited shear lips and significant localized necking (more than 50% thickness reduction), (ii) a fracture toughness that linearly increases with increasing thickness (in the range of 0.5–5 mm). The different contributions to the work expended during fracture of these materials are separated based on dimensional considerations. The paper emphasises the two parts of the work spent in the fracture process zone: the necking work and the “fracture” work. Experiments show that, as expected, the work of necking per unit area linearly increases with thickness. For a typical thickness of 1 mm, both fracture and necking contributions have the same order of magnitude in most of the metals investigated. A model is developed in order to independently evaluate the work of necking, which successfully predicts the experimental values. Furthermore, it enables the fracture energy to be derived from tests performed with only one specimen thickness. In a second modelling step, the work of fracture is computed using an enhanced void growth model valid in the quasi plane stress regime. The fracture energy varies linearly with the yield stress and void spacing and is a strong function of the hardening exponent and initial void volume fraction. The coupling of the two models allows the relative contributions of necking versus fracture to be quantified with respect to (i) the two length scales involved in this problem, i.e. the void spacing and the plate thickness, and (ii) the flow properties of the material. Each term can dominate depending on the properties of the material which explains the different behaviours reported in the literature about thin plate fracture toughness and its dependence with thickness.