U of C researchers investigate: Are female bones more likely to crack under pressure?

By Leonie O’Sullivan, June 29 2023—

From periods to the patriarchy, females have a lot to put up with. On top of all this, females are four times more likely than males to endure stress fractures. U of C Ph.D. candidate Olivia Bruce, under the supervision of Dr. Brent Edwards, has provided answers as to why this is the case.

Repetitive weight-bearing activities such as running-intensive sports can lead to an accumulation of microdamage in our bones. If this damage is given insufficient time to heal, stress fractures or little cracks in our tibiae and fibulae can occur — just like if a small chip in a car windshield is left unrepaired, it can lead to a crack. The tibia or shin bone is the second longest bone in our bodies, connecting our knees to our ankles. The fibula is the smaller bone in our lower extremities, parallel to the tibia. Take a look at a 3D model of a full human tibia and fibula here.

Stress fractures are commonly observed in runners and military personnel and can take six to eight weeks to heal, sometimes even requiring surgery. This can result in time off work or even having to retire at a young age from sports, leading to physical, financial and psychological hardships.

Last year Bruce and Edwards, alongside fellow researchers from the U of C Faculty of Kinesiology and the McCaig Institute for bone and joint health, highlighted tibial-fibular differences between females and males. In this study they used a statistical shape model (SSM), which they had previously developed in 2021 to predict the geometries of the tibial-fibula complex.

This SSM was trained off of CT scans to be able to predict what a bone looks like, without costly instrumentation but from nine-14 anatomical landmarks, identified either through touch or skin-mounted motion capture markers. The SSM was upgraded to a statistical appearance model (SAM), which characterizes bone density variations within a population. Computational models were used to determine muscle and joint forces when running.

Using these statistical and computational models, Bruce found that among 48 young and active adults (20 females and 28 males), there was an average of 5.5 and 41.3 percent greater peak strain and strained volume respectively, in females compared to males, which may be the cause of higher numbers of stress fracture in females. Bruce found that the females in this study had narrower tibiae compared to the males, which would contribute to greater strain. The female tibiae also had smaller condyles — condyles are the M-shaped rounded end of the bone. Females had greater cortical bone (the strong, compact outer layer of bone) density and a smaller cortical thickness at the top and bottom of the straight section (or diaphysis) of the tibia. 

One year later, Bruce and Edwards have published yet again in the journal Bone. This cross-validation study enlisted a new group of 30 young and active adults (15 females and 15 males) to verify their earlier findings. This study confirmed their previous claims of sexual dimorphism affecting the tibia width, bone mineral density and cortical thickness resulting in enhanced peak strain and strained volume in females. Sexual dimorphism is the differences between sexes of the same species. 

If you participate in running-intensive activities, you may be asking yourself — What can I do to prevent stress fractures?

Proper nutrition is essential for healthy bones. Vitamin D and calcium are vital nutrients. In the summer, you can get enough Vitamin D from sun exposure (while using sunscreen!), but in the darker months, you may need to incorporate some vitamin D-rich foods like fish, eggs and mushrooms. Seeds, cheese and yogurt are excellent calcium sources. When participating in sports, ensure that you follow an incremental training plan and don’t take on too much too soon. Switch it up and try out some ball sports like soccer or basketball, as these have been shown to promote bone development.

Know the signs of stress fractures. Tenderness begins in a localized area and becomes more painful over time. You may notice swelling in the affected area and less pain when resting. If you think you may have a stress fracture, make sure to see a doctor to avoid nasty complications. While waiting for medical attention, remember the RICE method — rest, ice, compress and elevate the affected area.