Osteoporosis gives rise to fragile bones that have higher fracture risks due to diminished bone mass and altered bone microarchitecture [1]. Mechanical loading mediated bone adaptation has demonstrated promising potentials as a non-pharmacological alteration for both osteogenic response and attenuation of osteopenia [2]. Intramedullary pressure (ImP) has been proposed as a key factor for fluid flow initiation and mechanotransductive signal inductions in bone. It is also suggested that integration of strain signals over time allows low-level mechanical strain in the skeleton to trigger osteogenic activities. The potential bone fluid flow induced by strain and ImP mediates adaptive responses in the skeleton [3]. Previous in vivo studies using oscillatory electrical stimulations showed that dynamic muscle contractions can generate ImP and bone strain to mitigate disuse osteopenia in a frequency-dependent manner. To apply ImP alteration as a means for bone fluid flow regulation, it may be necessary to develop a new method that could couple external loading with internal bone fluid flow. In order to further study the direct effect of ImP on bone adaptation, it was hypothesized that external dynamic hydraulic stimulation (DHS) can generate ImP with minimal strain in a frequency-dependent manner. The aim of this study was to evaluate the immediate effects on local and distant ImP and bone strain induced by a novel, non-invasive dynamic external pressure stimulus in response to a range of loading frequencies.

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