What is a stress fracture?

Stress fractures occur when the normal equilibrium of healthy bone turnover shifts in favour of bone breakdown with insufficient rebuilding of the bone matrix. This can happen in two broad scenarios. Firstly, if the bone density is normal but it is loaded too much we call this a fatigue stress injury. Secondly if the bone is already less healthy and dense we may call this an insufficiency injury.

Picture of osteoblast cells

A fracture means that the bone has developed a crack of the cortex but we do often see bone stress before a crack occurs- we call this a stress response (MRI is the most frequently used investigation). For many areas of the body where this happens we treat the injury in the same way- but some areas are at more risk than others and this can lead to more restriction in activity.

Most of the stress injuries that I see in clinic are the fatigue-type cases- when the amount of activity performed has been too much for the bone involved. For example, a runner who has increased their frequency and/or volume of running too much. There may have been insufficient rest and the bone has not had enough time to rest fully between training sessions. In running, stress fractures seen include the tibia(shin), the calcaneus(heel bone), metatarsals of the foot plus several others.

Different sports and activities may lead to different stress injuries and may be unique to that activity. For example- a stress fracture of the pars interarticularis in the spine may be caused by repetitive extension needed in cricket fast bowling. Another example would be a wrist stress fracture in a gymnast who repeatedly loads the wrist.

Sometimes we may see a stress injury in a patient who has lower bone density and this can be called an insufficiency fracture. Essentially here the bone is already weaker so it takes less load/force to injure the bone. Most people have heard of osteoporosis- this refers to significant thinning of the bone. On the spectrum between normal bone and osteoporosis is a condition called osteopenia where a milder loss of bone density may occur. Risk factors for lower bone density may include smoking, excessive alcohol intake, prolonged sedentary behaviour, certain medications, primary bone disorders and a family history of osteoporosis.

In female athletes it is important to ask about menstrual history plus dietary intake. In some cases if insufficient calories are ingested this can lead to possible weight loss- and in more prolonged cases this can affect the hormonal profile of the athlete. This can lead to disruption of the menstrual cycle and increase the risk of bone injuries such as a stress fracture. If there is a possible link in my patients to this then I will arrange certain investigations. They can also be needed in men and in patients who may have had a history of previous stress fractures.

A DEXA bone scan involves taking x-rays of the spine and hip to determine the level of bone density. If needed I will usually arrange some blood tests as well- and this will include calcium plus vitamin D levels as they can be lowered in the context of a stress fracture.

I will discuss management of stress fractures in more detail in a future blog.

Dr Michael S. Burdon

20-7-2021

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