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An engineer and a surgeon were talking about hip fractures…

Some time ago, a surgeon explained to an engineer that he was researching better ways to identify people with a high risk of fracture. He had a large collection of femoral heads from people who had had hip replacement surgery. The engineer asked, “Have you looked at the fracture surfaces?” The surgeon replied, “No… would that be useful?”

As well as making a handy anecdote about the importance of an engineering perspective in healthcare, this conversation eventually led to my master’s project in the structural analysis of bone.

Bone is a strange and fascinating tissue. It grows, develops and reconstructs itself throughout our lives. Inside the ends of long bones like the femur, bone has a spongy structure, which is formed of thousands of tiny beams of bone called trabeculae. The trabeculae develop in response to the stresses they experience. In the femoral head (the end of the femur which fits into the hip joint), this makes for a structure highly optimised to carry body weight, but ill-equipped for sideways impacts such as falls.

trabeculae
Typical carcinoid trabecular pattern

Combine this with the fact that as we age, our bones become less dense, and it becomes clear why falls can be so dangerous for older people. The average age of a hip fracture patient is over 80, and it is the commonest cause of injury-related death in the UK.
The standard approach to manage people at risk of fracture is to monitor their bone density. If it drops below a certain level, the patient is diagnosed with osteoporosis and may be prescribed drugs or exercises to encourage bone growth. While this works fairly well, it doesn’t cover the whole picture.

So, which is more stable: a few carefully positioned beams, or lots of beams arranged at random?

Working with finite element models of bone samples from hip fracture patients, I was able to show that a combined measure of bone density and trabecular orientation may be a better predictor of bone stiffness (resistance to deformation by an applied force) than density alone. Future work in this area could lead to even more accurate risk assessment for fractures, possibly identifying people who would otherwise have gone untreated.

Isobel’s research was recognised by the Institute of Structural Engineers through their MSc Research Grant scheme and received the award for best poster.

isobel lab work

Isobel is a mechanical engineer at Team. Working across a variety of projects, she applies her mechanical and bioengineering background to areas including math modelling.

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