Trabecular and cortical bone density and architecture in women after 60 days of bed rest using high-resolution pQCT: WISE 2005

Abstract

Prolonged bed rest is used to simulate the effects of spaceflight and causes disuse-related loss of bone. While bone density changes during bed rest have been described, there are no data on changes in bone microstructure. Twenty-four healthy women aged 25 to 40 years participated in 60 days of strict 6-degree head-down tilt bed rest (WISE 2005). Subjects were assigned to either a control group (CON, n ¼ 8), which performed no countermeasures; an exercise group (EXE, n ¼ 8), which undertook a combination of resistive and endurance training; or a nutrition group (NUT, n ¼ 8), which received a high-protein diet. Density and structural parameters of the distal tibia and radius were measured at baseline, during, and up to 1 year after bed rest by high-resolution peripheral quantitative computed tomography (HR-pQCT). Bed rest was associated with reductions in all distal tibial density parameters (p < 0.001), whereas only distal radius trabecular density decreased. Trabecular separation increased at both the distal tibia and distal radius (p < 0.001), but these effects were first significant after bed rest. Reduction in trabecular number was similar in magnitude at the distal radius (p ¼ 0.021) and distal tibia (p < 0.001). Cortical thickness decreased at the distal tibia only (p < 0.001). There were no significant effects on bone structure or density of the countermeasures ( p ! 0.057). As measured with HR-pQCT, it is concluded that deterioration in bone microstructure and density occur in women during and after prolonged bed rest. The exercise and nutrition countermeasures were ineffective in preventing these changes. ß

Effects of Sex and Gender on Adaptation to Space: Musculoskeletal Health

“…There is little evidence, however, on whether there is a sex difference in rates of bone loss with unloading or in the rate or magnitude of recovery therefrom. While the effects of bed rest on BMD and/or bone metabolism have been examined separately in men 13,14 and in women, 15,16,17 there have been no human studies that have been statistically powered to make direct sex comparisons. In one 17-week bed rest study that included both men (n = 13) and women (n = 5) at one of 10 sites measured (calcaneus), bone loss was markedly less in women than men.…”

“…13 Volumetric BMD and bone geometry of tibial cancellous and cortical compartments have been evaluated after prolonged bed rest using peripheral quantitative computed tomography (pQCT) in men 13,15 and high-resolution pQCT in women. 16 The small gender differences observed in the bone loss rates at those tibial sites are within the reported precision for these pQCT variables. Side-by-side investigations using rodent hindlimb unloading (a commonly used surrogate for microgravity) reveal greater cancellous bone loss in skeletally mature female mice 18 and a distinct effect of starting values (mice with greater bone volume at the start lost less bone).…”

In vivo loading model to examine bone adaptation in humans: A pilot study

“…This region had substantial overlap with the region typically selected for analysis in high resolution peripheral QCT (HR-pQCT) studies. 17 The total radius was defined as the 45 mm region proximal to the subchondral plate, as well as everything distal to and including the subchondral plate. The location of the subchondral plate was objectively defined for the first scan (week 0) as the transverse CT slice with the largest cross-sectional area.…”

Gene Expression Responses to Mechanical Stimulation of Mesenchymal Stem Cells Seeded on Calcium Phosphate Cement

“…The distributions of radial (r rr ), circumferential (r yy ), and shear (s yr ) stress components shown in Figure 2A were calculated with reference to the load factor (Eq. [1], where P is the applied load, R the radius of the circular sample, and t its thickness):…”