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Bone Architecture and Activity

 

Bone is structured in two ways. The hard outer surface of bone is compact (cortical) bone. Inside this there is a honeycomb structure known as trabecular bone. The combination of the two makes bone strong but lightweight. Bone slowly adapts its quantities and structure in response to physical activity. For example, the cortical bone of a tennis player’s serving arm will be thicker than the bone of the non-serving arm. By looking at the shape and architecture of bone, we can assess the physical activity patterns of people in the past. Measurements of bone thickness and shape tell us about bone strength in different directions, including when a bone is compressed, stretched, or twisted. Studies have shown that people who lived relatively sedentary lives have lower quantities and quality of trabecular bone in their lower limbs. We can compare between men and women to tell us about the sexual division of labour, but also between high and low status people, and over time. Bone shape and strength can also be affected by disease and environment.

 

To study bone architecture, we scanned the femurs and humeri from selected medieval people. This type of computed tomography relies on X-ray techniques, but with considerably higher levels of radiation compared with clinical equipment. The bones are placed in an acrylic tube in the centre of a large cabinet, between the energy source and a detection panel. This detection panel recognises different densities: denser tissue absorbs more of the emitted energy. By slightly rotating the bone after each image capture (usually between 0.3-0.5°), we get a view from all sides, which allows for a digital reconstruction of the whole area scanned.

Cross section of bone

Cross section of femur showing cortical bone (a)

and trabecular bone (b).

Image: Bram Mulder

Functional analysis revealed little differences among the different groups townspeople, Friars, and people living on charity. This reflects the fact that, while their lives were socially differentiated, they all involved habitual physical work stressing the skeleton in some ways. As people living and working in a town, they shared a homogeneous lifestyle compared to other historic populations functional morphometrics has been used to study. This was true for both men and women, though older townswomen tended to lose bone mass, perhaps an effect of changing diet, metabolism and activity as they aged. People living in the Hospital of St. John were similar, but they also included a wide range of variation perhaps reflecting their wide range of life stories, including townspeople, lifelong poor and ill people, and University scholars.

Bone slices

Slices taken through the middle of three different femurs (thigh bone).

 

Note the difference in cortical bone thickness as well as overall shape. The femur on the left comes from somebody less mobile than that of the person on the right, where forward and backward muscle movement has made the bone more oval.

Image: Bram Mulder

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