Risk Factors for the Evasive Fibular Stress Fracture

Awareness of stress fractures and their season-ending effects has become very prevalent in the running community. Runners are getting a sense of what to look for if they are worried about a possible stress fracture. This is helpful to a degree, but recently we've been seeing an increase in less-common stress fracture types. One in particular, fibular stress fractures (the other lower leg bone next to the tibia), has been showing up in at Custom Performance more frequently.

This is interesting for a couple of reasons:

1) The tibia—not the fibula— is the primary weight-bearing bone of the lower leg. Makes sense, right? You’ll hear about tibia injuries more often, usually in the form of injuries like stress fractures or shin splints.

2) How you move can identify what bones are at a higher risk for stress fracture. So my question was, what do these runners who are getting fibular stress fractures have in common in their movement patterns?

After reviewing some research, here are three potential factors that could make the fibular stress fracture more likely due to individual qualities:

1) Flat feet
2) "Rearfoot varus"
3) Weak or injured posterior tibialis tendon/muscle

"Rearfoot varus" is basically when the heel collapses to the outside of the rest of foot. It almost looks like the foot gets squished down and the heel gets pushed outside as a result. This, like the quality of “flat feet”, is often the result of hypermobile feet. Both of these factors change how impact forces are applied to the foot and therefore the rest of the body. 

The third factor, a weak/injured posterior tibialis muscle, couples well with rearfoot varus and flat feet. The posterior tibialis has a very important job; supporting the arch of the foot and actively lift the midfoot. If this muscle isn’t working, the foot becames more “flattened” during activity. Combine that with an already flat foot, and how impact forces are applied to the body can change dramatically.

So what’s the point of all of this seemingly nit-picking information? Awareness! If you suspect a possible stress fracture on the outer lower leg bone (fibula!) and can recognize these factors, you’ll be more likely to address the injury before it becomes even more serious. More knowledge = runners making smart decisions = less injuries.

Dr. Cathlin Fitzgerald, PT, CSCS