Can principles from engineering provide a broader understanding of how the human skeleton works and be used to help prevent a common and often consequential event for people as they age—bone fractures?
Research from a team of investigators that includes orthopedic surgeons and mechanical engineers suggests that, yes, looking at how engineered materials, such as metals and ceramics, function over time can illuminate how bones behave as a person ages.
In particular, the research focuses on fatigue as the missing link between bone fragility and fracture as aptly stated in the title of a recent study, “Fatigue as the Missing Link Between Bone Fragility and Fracture.”1 Fatigue, used in terms of fracture mechanics, implies that a material’s mechanical resistance will decrease over time as a result of repetitive, or cyclic, loading. Fatigue failure refers to the number of cycles, or the time needed, for the material to be damaged via crack growths that cause the material failure.
Applying this to the human skeleton, the investigators propose that some bone fractures in older people are the result of cyclic loading, producing microcracks that, over time, result in fatigue fracture. Older people are more susceptible to this type of fracture because of the well-known fact that bone remodeling and repair slows with age, but also, the investigators suggest, because the quality of bone in older people is decreased, evidenced by the decreased capacity of bone to handle weight-bearing loads.
“Most people think the elderly break a bone because they fall,” says lead author of the study Claire Acevedo, PhD, assistant professor, Department of Mechanical Engineering, University of Utah, Salt Lake City. The research, she says, suggests the “bone is already damaged by microcracks before they fall, so the fall may occur on an already partly broken bone or the fall may even be induced because the bone breaks at some point.”
New Insight into Skeleton Pathology
Calling the research fascinating, Thomas Parker Vail, MD, James L. Young Professor and chairman, Department of Orthopaedic Surgery, University of California, San Francisco, says it represents a new look at how bone responds and communicates within its own structure, as well as outside that structure.
Through imaging, he says the investigators have shown the tiny canals that connect osteocytes within the bone. If you overlay this imaging on images of neuronal networks, he says, the similarity is astounding.