Ontogenetic growth processes in human long bones are key elements, determining the variability of adult bone structure. This study seeks to identify and describe the interaction between ontogenetic growth periods and changes in femoral and tibial diaphyseal shape. Femora and tibiae (n 5 46) ranging developmentally from neonate to skeletally mature were obtained from the Norris Farms No. 36 archeological skeletal series. High-resolution X-ray computed tomography scans were collected. Wholediaphysis cortical bone drift patterns and relative bone envelope modeling activity across ages were assessed in five cross-sections per bone (total bone length: 20%, 35%, 50%, 65%, and 80%) by measuring the distance from the section centroid to the endosteal and periosteal margins in eight sectors using ImageJ. Pearson correlations were performed to document and interpret the relationship between the cross-sectional shape (I max / I min ), total subperiosteal area, cortical area, and medullary cavity area for each slice location and age for both the femur and the tibia. Differences in cross-sectional shape between age groups at each cross-sectional position were assessed using nonparametric Mann-Whitney U tests. The data reveal that the femoral and tibial midshaft shape are relatively conserved throughout growth; yet, conversely, the proximal and distal femoral diaphysis and proximal tibial diaphysis appear more sensitive to developmentally induced changes in mechanical loading. Two time periods of accelerated change are identified: early childhood and prepuberty/adolescence. Anat Rec, 296:774-787, 2013. V C 2013 Wiley Periodicals, Inc.Key words: bone biology; ontogeny; cortical bone geometry Growth-related changes in human long bone morphology and biomechanical features are key elements for understanding the variability and functional significance of adult bone structure (Smith and Buschang, 2004;Ruff, 2005). The heterogeneity of long bone diaphyseal shape and size variation occurs during ontogeny and is
The mechanostat hypothesis, first proposed by Harold Frost in 1987, describes a regulatory mechanism within bone that functions to maintain bone tissue mass and organization via metabolic action in response to mechanical stimuli. The mechanostat operates like a home thermostat, with minimum and maximum strain thresholds serving as triggers to stimulate bone formation or resorption; this allows bone to maintain its own tissue mass and distribution appropriate to the mechanical demands it habitually experiences. The mechanostat is a critical element of bone functional adaptation theory, serving as the mechanism that allows bone to sense and respond to its strain environment.
According to the US Bureau of Labor Statistics, the average age of retirement is 62. While many retirees may have employer-provided or other access to healthcare, others have limited access to affordable care until full Medicare eligibility at 65. Regardless of access, retirees with toxic occupational exposures may not have providers with specialized knowledge of tests or diagnoses for exposure-related health conditions, especially those with long-latency. The National Supplemental Screening Program for U.S. Department of Energy Former Workers is described here as a nationwide program providing recurring (every 3 years) integrated health screenings designed to identify both occupational and non-occupational conditions in the context of exposure so that early identification can enable appropriate and timely diagnoses and treatments to improve health outcomes. Since September 2005, there has been 18,518 initial exams for former workers, of whom 5,461 returned for rescreening exams through April 2019. The average age of those returning was significantly younger at initial exam (63.4 years) compared to those who did not return (65.1 years). The most common occupational condition was noise-induced hearing loss not attributable to natural, age-related loss (67%). Rare and long-latency occupational health conditions, such as asbestosis or silicosis, were identified at rates expected (1-4%). The most common non-occupational condition was elevated body mass index (BMI>25, 77.3%), followed by hypertension (20.7%), of which 50% had no prior knowledge or clinical diagnosis. In conclusion, occupational health surveillance programs can provide value for identifying non-occupational health conditions and as a supplementary source of health information and care.
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