Stress Fracture – What is it, How to treat it and How to prevent it

Most athlete's have at least heard the term stress fracture and it is more than likely that they or someone they know has experienced this injury. A stress fracture can be very frustrating due to it's insidious onset and nature along with unclear evidence about how or when return to activity. In this article several topics will be explored including, the mechanism and fundamentals of a stress fracture injury; How it is diagnosed; How it is treated; How to return to activity; And how to prevent it from reoccurring.

What is a Stress Fracture?
Simply put, a stress fracture is a microscopic injury to a bone, typically due to over use. Like much of the human body a bone is metabolically active and is constantly being broken down and rebuilt. However, additional stress, such as running, places greater demand on the healing and restorative properties of the bone. A stress fracture occurs when breakdown exceeds rebuilding; typically this is due to repeated stress with inadequate rest and recovery.

The analogy of a paper clip has been used to describe a stress fracture within a bone. If you repeatedly bend a paper clip no single bend is enough to break the paper clip, but the sum of the repeated forces weakens the structure and eventually one additional bend causes the fracture. However, it should be noted that a paper clip does not heal and grow stronger after each bend, where as a bone will, so a stress fracture not simply a matter of wear and tear. Additionally, a bone has other metabolic demands other than skeletal structure and calcium, vitamin D or other metabolic alterations can impact bone health.

A stress fracture is a common athletic injury, typically observed in runners and typically in the lower leg and foot. In fact, it is estimated that stress fracture make up 15% of all running injuries and 1-3% of athletic injuries as a whole.

How does it occur?
Stress fractures can be traced to sudden or dramatic changes in activity volume , intensity, equipment (new/old shoes), and surface or terrain (pavement, hills ect.)

As stated above bone is metabolically active and is constantly being broken down and rebuild. Bone remodels (rebuilds) in direct response to the forces that are applied; "use it or lose it" so to speak. The forces applied during running are a direct stimulus for greater bone repair and growth. However, there is s physiologic limit for bone repair, it can only rebuild so fast. If the stress applied is greater than the bone's ability to heal, microscopic damage occurs and often results in a stress fracture.

Keep in mind that abnormally weak bones, or bones that are unable to repair and remodel as quickly will tolerate less stress and are at greater risk of injury. The typical example here is osteopenia, where bones are simply weaker. As well as athlete's with eating disorders where they deplete their fat stores and as a result inhibits estrogen production, which in turn, leads to greater bone loss than growth.

How does it present and how is it diagnosed?
Typically the presenting symptom of a stress fracture is bone pain, often times in combination with over use or sudden change in use. The shin is the most common place for a stress fracture to occur. Pain is typically localized to the bone, crescendo in nature with activity and does resolve shortly after stopping activity. In fact pain may last for hours to days after stopping activity and there may even be pain at rest that is not associated with activity at all. Typically, pressing on the affect area will illicit pain as well. However, none of these symptoms are completely diagnostic and as a result medical imagining is often required.

Plain x-rays appear normal, especially in the early stages of a stress fracture because the trauma is microscopic. However, if the stress fracture is older, then a callus and/or sclerotic tissue, which is the result of metabolic healing activity, may be visible with plain x-ray. To diagnosis a stress fracture in the early stages, when the information is most useful, an MRI or bone scan are required. A bone scan has been the gold standard until recently when MRI has been utilized more often. The problem with both of these imaging modalities is that they typical show abnormal tissue for prolonged periods of time, well after the stress fracture is actually healed. As a result MRI and bone scan are appropriate to make an initial diagnosis, however, they not useful for indicating when recovery is complete and an individual can return to activity.

How is it treated and how to return to activity?
The only effective treatment for an over use injury is relative rest. It is not required or even recommended to totally rest because muscle atrophy can occur and as discussed early some stress will aid the healing process. Rest simply needs to allow for bone remodeling or catch up to bone injury or breakdown. Every injury and every athlete's rest and treatment will vary, however, in general it is recommended that the inciting activity, typically running, be discontinued for 4-12 weeks while maintaining other activities to maintain fitness and overall health. Occasionally, crutches can be used to completely unload the affected area if injury is sever or the stress of weight bearing is too great.

Return to activity must be very gradual and this is typically the most challenging part for many athletes. Placing too much stress on a weak or healing bone, too soon can set the recovery process back weeks to months. Often a coach or strict activity plan can aid an athlete in return to activity and help prevent them from re-injury. There is no test or indicator that will reliably tell an athlete and physician when a stress fracture is fully healed and ready to return to activity. As a result, it is better to air on the conservative side resting a bone for longer than is actually necessary and very gradual return to activity. Typically the first running an athlete will engage in is several rounds of a 30 second easy jog with 1-2 minute walking recovery between. If that goes well the jogging interval can gradually be increased. However, if within a few weeks there is no residual pain or problems with activity then running and athletic levels can progress at faster rate with a full recovery expected.

Another aspect to recover and return to activity should be an assessment of calcium, vitamin D and other indicators of bone metabolism to explore possible metabolic or other causes of the stress fractures. Although, not common, underlying vitamin, mineral or other deficiencies can make an individual more susceptible to a stress fracture.

Prevention:
Stress fractures cannot be totally prevented, however, there are several steps that can help to avoid them. Keep activity level reasonable and do not make sudden or drastic changes. Regular rest and recovery should be built into any training program. Listening to your body and stopping activity or rest at the earliest sign of an injury or general over use. Yearly medical check ups, typically early is the training year, including a metabolic profile can help make sure you are healthy and ready for the demands of training.

Summary:
Stress fractures are microscopic trauma caused to bone due to repeated stress and over use. An MRI or Bone scan is required for diagnosis. Typically they require rest with gradual and progressive return to activity. Fully return to activity is possible with minimal is any long term consequences.

Alex M. McDonald, MD is a professional triathlete, First Endurance Research Board Member, and endurance coach at Fast Forward Triathlon. Alex's professional interests lie in coaching endurance athletes, sports medicine and exercise physiology. He obtained his MD degree from the University of Vermont. Prior to medical school, Alex graduated from Connecticut College with an emphasis on both the biological and social sciences. He currently trains and lives, with is wife and daughter, in Durham, NC.

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