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The skeletal effects of historical transitions in lifestyle

Periodic Reporting for period 1 - TRANSITIONS (The skeletal effects of historical transitions in lifestyle)

Reporting period: 2019-09-02 to 2021-09-01

During life, the distribution of cortical bone is influenced by loading history and bone remodelling seems to be significantly associated with high-frequency daily action. TRANSITIONS explored the skeletal adaptions in distinctive recent human groups characterized by different loading history, age and body size. In fact, understanding how different lifestyles affect skeletal form is crucial to reconstruct physical activity behaviour in past human populations. In addition, the detailed study of a wide collection of recent individuals returns important information to understand how diet, a sedentary lifestyle and longevity affect skeletal form with useful implications for musculoskeletal health.
This is important for society because scientists have focussed on the analysis of long bone morphology to study how mechanical loadings impact on skeletal form, since the foundation of biomechanics. This has relevance to understanding how our lifestyles influence or skeletal health, which might allow novel insights into the lives of past populations and have value in predicting the prospects of fracture with aging in modern society. In an aging society, these questions become even more relevant. This study provides new insights and new tools for future studies. The shaft of long bones is commonly analysed on a few levels (i.e. mid-shaft). One of the aim of TRANSITIONS is to overcome this issue providing a new software capable to analyse the entire diaphyseal cortical thickness processing multiple cross-sections along the entire length of the shaft.
Beside to the methodological innovation, the usage of an extensive collection of recent deceased individuals with known loading history allows the overall objective of gaining greater understanding of how lifestyle, age and body mass affect bone remodelling during the life.
TRANSITIONS was structured into a developmental and applicative phase. The first part of the project focussed on the creation of a new open-source toolkit (morphomap) providing functions to extract from CT data, the segmented long bone of interest and based on that, morphometric and biomechanical parameters together with maps of cortical bone distribution along the entire diaphysis of long bones (Figure 1).
The Covid pandemic had a major impact on my ability to travel to gather CT data from archaeological populations as intended. Therefore the focus was shifted more towards what could be achieved by working remotely – detailed software development and assessment of data from living populations available in a novel database, accessible via the internet to establish the baseline understanding in modern populations that can be applied to archaeological material, which we expect will become available again in the next year or two. This shift was actually very beneficial in that by first understanding how bones adapt to activity and body proportions in a well characterised modern sample with detailed life history and activity records we are now in a much better position to interpret the less well characterised archaeological material by reference to this unique modern sample.
During the project an extensive database of 3D models of long bones was built from CT data of recently deceased female and male individuals (NMDID database). In detail 3D models of the humerus and femur from more than 200 individuals were generated. The 3D models were processed using the new software, developed further within the project, morphomap to extract from the entire diaphysis the information related to shape, biomechanical parameters and cortical thickness.
The distribution of cortical bone in the femora of males and females is mainly influenced by body proportions (weight, height and long bone length) and age. Loading history in recent human individuals does not appear to influence significantly the distribution of cortical bone. In women, age influences more strongly the cortical thickness of the femur than any other variable, probably in relation to osteoporosis (Figure 2). Interestingly, the analysis of the upper limb reveals that males are more asymmetric than females. In adults, asymmetry of cortical thickness in the humerus decreases with increasing of age.
In conclusion, the project TRANSITIONS found that factors external to the occupational and recreational loading history of an individuals such as weight, height and age are most important in influencing the overall thickness and distribution of cortical bone in the femur and humerus. In addition, some of these variables have an impact on the distribution of the cortical bone in different ways.
One of elements of novelty in TRANSITIONS is the creation of a new open-source software capable of analysing in detail the diaphysis of long bones. As a result, today, morphomap boasts more than 10,000 downloads from CRAN servers and it is being used in processing long bones in humans but also in primates, small carnivorans and even Neanderthal teeth. The real impact of mechanical loading on the distribution of the cortical bone (i.e. higher loadings lead to the thickening of the cortex) has long been debated in the literature. At present, the findings from TRANSITIONS support the theory that rather than occupational and recreational mechanical loadings, other factors such as weight, height and age have more impact.
Lastly, one of the novelty of TRANSITIONS is the possibility to map via morphomap how variables influence the distribution of the cortical bone in long bones. TRANSITIONS found a different quantitative and qualitative impact of ageing in the femur bone from males and females. Potentially, these findings have a potential impact in medicine and in social studies. The results from TRANSITIONS should be used for public education and information of the consequences of unbalanced diet for our health.
Cortical thickness differences between 18 and 50 years old
Functionalities of morphomap