Ontogeny of long bone cross-sectional geometry has lasting effects on adult bone structure. Growth and development of bone is influenced by biological and mechanical factors but the importance of these factors is poorly understood. A study of prenatal, neonatal and infant development in a bone with simple loading patterns, may improve our understanding. Five vertebral columns aged between 6 months prenatal to 2.5 years postnatal, were analysed to quantify the changes in trabecular architecture before and after birth. Several measures were collected including trabecular: thickness, bone volume fraction, connectivity density, number, structure model index and anisotropy. The findings show that in the first year after birth there is a substantial loss of bone volume via decreasing trabecular thickness and number, which tends to increase after 1.2 years. This sequential pattern of development may be a functional response to the initial requirement for calcium mineral homeostasis before birth, followed by the need for trabecular architecture to adapt to mechanical loading after birth. Calcium is essential for growing neonates and therefore osteoclastic resorbtion is up regulated by increasing parathyroid hormone levels. This may account for the loss of bone between 0–1 year. At one year infants begin to walk bipedally, thus weight bearing and ground reaction forces increase. The stable bone volume and increase in organisation of trabecular architecture after one year may reflect increasing weight bearing and ground reaction forces. These findings suggest that nutritional requirements after birth may have a stronger influence on vertebral trabeculae architecture than learning to walk.
Senile kyphosis arises from anterior ‘wedge’ deformity of thoracolumbar vertebrae, often in the absence of trauma. It is difficult to reproduce these deformities in cadaveric spines, because a vertebral endplate usually fails first. We hypothesise that endplate fracture concentrates sufficient loading on to the anterior cortex that a wedge deformity develops subsequently under physiological repetitive loading. Thirty-four cadaveric thoracolumbar “motion segments,” aged 70–97 yrs, were overloaded in combined bending and compression. Physiologically-reasonable cyclic loading was then applied, at progressively higher loads, for up to 2 hrs. Before and after fracture, and again after cyclic loading the distribution of compressive loading on the vertebral body was assessed from recordings of compressive stress along the sagittal mid-plane of the adjacent intervertebral disc. Vertebral deformity was assessed from radiographs at the beginning and end of testing.Introduction
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Vertebroplasty helps to restore mechanical function to a fractured vertebra. We investigated how the Nine pairs of three-vertebra cadaver spine specimens (aged 67–90 yr) were compressed to induce fracture. One of each pair underwent vertebroplasty with PMMA, the other with a resin (Cortoss). Specimens were then creep-loaded at 1.0kN for 1hr. Before and after vertebroplasty, compressive stiffness was determined, and stress profilometry was performed by pulling a pressure-transducer through each disc whilst under 1.0kN load. Profiles indicated intradiscal pressure (IDP) and compressive load-bearing by the neural arch (FN) at both disc levels. Micro-CT was used to quantify cement fill in the anterior and posterior halves of each augmented vertebral body, and also in the region immediately adjacent to the fractured endplateIntroduction
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