Bone fatigue fractures
Hairline fractures appear in bones when they are subjected to repeated mechanical stress. As this microscopic damage is often imperceptible unless the bone actually breaks, it is important to find a method capable of detecting, preventing or even treating it. By Anton Vos
Stress fractures account for almost 20% of all sports injuries. They are caused by chronic mechanical stress imposed on the skeleton and present a specific problem: the precursory injuries are extremely fine cracks which are virtually undetectable using medical x-rays prior to an actual fracture. To learn more about their occurrence and the mechanisms that lead to them spreading in the bone tissue, Claire Acevedo, a post-doctoral researcher at the Lawrence Berkeley National Laboratory (Berkeley University) in California, recently tested a mouse model capable of reproducing and investigating the phenomenon. A publication on the subject is in preparation.
It is in weight-bearing bones such as the tibia, the fibula and the metatarsals that micro-cracks usually appear. They are as fine as a hair and spread slowly. "These stress fractures are particularly insidious because they affect healthy bones and occur in the absence of severe shock", explains Acevedo. Those most susceptible to them are elite athletes (runners, dancers, etc.) and members of armed forces subject to intensive training. In this case, the process of self-healing of the bone is not fast enough to prevent the accumulation of these cracks".
It’s not restricted to athletes, however; incidence increases with age, the risk of osteoporosis, the presence of certain diseases such as osteogenesis imperfecta (also known as brittle bone disease) or, paradoxically, long term medication against osteoporosis.
As they are undetectable under traditional medical x-rays, little is still known about the mechanisms of stress fractures in the complex micro-structure of bones. The only way to study their origins and their evolution as well as the ability of bone to resist and to repair itself is to conduct experiments on live animals. For this, Acevedo has chosen the mouse. "The micro-structure of the bones of pigs or dogs would be more similar to that of the human bone", she says. "But those experiments would have been much more complicated to set up and would take more time than working with rodents".
(From "Horizons" no. 102, September 2014)