Stress Fracture – Part 1 – What is it?
Sally likes to run for exercise and does the occasional 5k. She decides to run an upcoming half marathon with a couple of her friends, and she starts a training schedule. All is going well, in fact, so well that sometimes Sally runs a little longer than her training schedule calls for – she loves her running! But then, Sally starts to notice some soreness in the front of her shins toward the end of her long runs. The feeling goes away soon after her run is done; she figures maybe it’s the shin splints that she’s heard of so many other runners getting. She decides to try some different shoes to try to fix it, and starts icing her shin after running. But the pain starts to be more intense during her long runs, and she’s noticing it during her shorter runs, too. She adds foam rolling to her post-run routine, but the pain just continues to intensify, and sometimes she even has to cut her long runs short because of it. She tries backing down her mileage some, and the pain reduces but doesn’t completely go away. She knows she’s a little behind her training plan, so she starts trying to increase mileage again to get ready for the race. But the pain flares back up during all of her runs, forcing her to back off her mileage again, and she starts to notice some pain when she isn’t running – particularly going down stairs. Now she’s really starting to be concerned that she may not be able to complete her goal race! How did this happen? Everything was going so well!
Sally decides it’s time to go to the doctor. An MRI shows a tibial stress fracture. The doctor puts her in a walking boot for 6 weeks, gives her an anti-inflammatory prescription, and tells her to stop running for the time being. Sally is shocked by this diagnosis, and disappointed to not only miss her goal race but that she has to stop running entirely for a while! Sadly, Sally has become one of the 20% of runners that develops of a stress fracture each year1.
So what exactly is a stress fracture, and what causes it?
A stress fracture is a break in the bone that forms over time, due to repeated overloading. (Fracture is just another word for broken bone.) This is different from how we usually think of a broken bone happening – like a fall or other sudden accident. In order to understand how stress fractures form, it is helpful to learn a little more about bone structure.
It’s often easy to think about bones simply as the rigid, fixed frame for our body – much like the frame of a car or a house. But living bones are actually responsive, becoming stronger or weaker according to the loads that are placed on them, similar to how our muscles respond to weight lifting. And, just like our muscles get sore and can even get injured when we lift more than we’re used to, bones can also become irritated when we load them up too much (say, by increasing our run mileage too quickly).
Let’s learn a little more:
Bones are made up of several concentric layers:
- Periosteum is the outer surface of dense cells. Periosteum has a nerve supply, some of which does penetrate into the rest of the bone. These nerves make the periosteum sensitive to stress. Tendons and ligaments attach to this periosteum, and the inner layer is responsible for bone growth and repair.
- Below the periosteum every bone contains a layer of compact bone, and then cancellous bone.
- The long bones such as the femur are hollow, a structure called the medullary cavity. It is lined by a soft layer called the endosteum, which is involved with bone repair.
The body is continually changing, and mechanisms exist to maintain a balance (homeostasis) of the various tissues and systems. Within this tissue homeostasis, cells die, and they are replenished in response to various environmental stresses. In the case of bone, there is a continuous process of remodeling in response to the stress placed on them. Osteoblastic cells break down bone tissue, and osteoclastic cells build up bone tissue. Normally, these cells work together in a balanced way to break down old or damaged cells and replace them with new cells as needed.
When too much stress is repetitively placed on bone, an imbalance can develop between the osteoblastic and osteoclastic cells. This imbalance leads to a stress fracture starting to develop from the outermost layer – the periosteum. If the stress is reduced, and homeostasis restored, healing will occur. Stress, typically, needs to be relatively-reduced rather than totally reduced (e.g. non-weightbearing). If too much load is taken off the bone, its remodeled structure will be weaker and it may not respond well to increased activity. However, if stress is not reduced enough, and homeostasis is not restored, the stress fracture can progress into the deeper layers of the bone. It can even progress into a traditional fracture if a high instantaneous load is placed at that fracture site. There is suggestion that this has happened to many athletes including basketball’s Kevin Wade with an open tibial fracture (Warning! The video of this injury is pretty gruesome, so YouTube at your own risk!).
This highlights how important it is to get a professional opinion of the problem, rather than “toughing it out” with potentially disastrous consequences. Once a stress fracture continues into a traditional fracture, it can be a complicated injury that requires surgery to repair.
Stanford University has created an MRI-based classification system for stress fractures2. There are 4 grades listed and further described in the video below:
- Grade 1: small periosteum edema
- Grade 2: increased signal in marrow cavity on T2 sequences
- Grade 3: marrow signal abnormalities seen on T1 and T2 sequences due to increased bleeding (This was Sally’s diagnosis!)
- Grade 4: Fracture line is present
The good news is that early grade stress fractures typically do not need surgery. Also, the earlier it is caught and properly managed, the less time it will take to heal. For instance, if Sally had backed off her runs enough to allow healing when she first started to feel pain during long runs, she might have needed less than a month of relative rest, compared to possibly several months of rest once she’s started to feel pain during her daily activities.
Ouch! I don’t want to have a stress fracture!!
In my next blog post, I will discuss symptoms and what to watch for, how stress fractures are diagnosed and treated, and risk factors. Research shows that 1 in 5 runners will develop a stress fracture every single year! Don’t be one of them!
- Tenforde AS, Kraus E, Fredericson M. Bone Stress Injuries in Runners. Phys Med Rehabil Clin N Am. 2016;27(1):139-49.
- Fredericson M, Jennings F, Beaulieu C, Matheson GO. Stress fractures in athletes. Top Magn Reson Imaging. 2006;17(5):309-25.
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