Stress Fractures in Endurance Athletes

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Stress fractures are one of the most feared injuries in the realm of endurance sports and they are also one of the most common sidelining injuries that such athletes face.

Rachel Biber Brewer, MD
Jeffrey Kreher, MD
Members AMSSM

Stress fractures are one of the most feared injuries in the realm of endurance sports and they are also one of the most common sidelining injuries that such athletes face.  Stress fractures of the lower extremity account for up to 15% of all injuries in runners. 

Symptoms
The typical history of a stress fracture is localized pain of gradual onset that is initially present during training activities.  A sign of a more advanced fracture is pain during non-weightbearing activities or walking.  There is often focal bony tenderness or swelling over the fracture site.

Etiology and location
Vigorous and repetitive physical activity that leads to excessive loading of bone beyond the bone’s ability to adapt and poor bone health are considered the primary pathological causes of stress fractures.  The responses to continued bone overload are bone strain (where bone resorption exceeds bone deposition), followed by microfractures, and ultimately complete fracture.  If the stress persists without adequate rest from activity, then incomplete healing can occur.  Stress fractures in endurance athletes most common occur in lower extremity due to the repetitive forces of running.  The tibia and metatarsal bones are most commonly affected, while the fibula, the navicular bone in the foot, pelvis, and femur are also encountered.

Risk factors
As is true with any overuse injury, stress fractures have a multifactorial origin.  Extrinsic factors, such as training frequency, duration, or intensity, along with improper equipment, are commonly associated with lower-limb stress fractures.  Training on certain terrains like asphalt or harder training surfaces is also a risk factor.  Failure to schedule rest days is a common culprit in developing stress fractures, which highlights the importance of periodization of training in any endurance sport.

Intrinsic factors include anatomic and biomechanical variables of each individual athlete.  For example, extremity malalignment and inappropriate gait have been implicated in developing stress fractures.  Other intrinsic factors include those related to gender and bone health.  Multiple studies show that women have a higher incidence of stress fractures due to several factors such as menstrual irregularities and lower bone mineral density. The female athlete triad (oligomenorrhea, disordered eating, osteopenia) has been associated with increased stress fractures.

High risk vs. Low Risk Stress Fractures
High-risk stress fractures are classified as having a high risk for incomplete healing or prolonged recovery.  Lower risk stress fractures tend to heal with 4-6 weeks of restriction from pain-producing activities (see table for examples of low and high risk stress fractures).

Diagnosis
Making the diagnosis of a stress fracture relies on your doctor taking a history of your injury and performing a physical exam.  Stress fractures are usually not visible on an x-ray unless they have been present for weeks.  MRI is the test of choice for diagnosis of stress fracture, replacing bone scans, because it gives anatomic information, does not involve radiation or an injection, and is usually easily obtainable.  However, some doctors safely diagnose certain stress fracture based on the history and examination.

Treatment
The first priority after establishing a diagnosis of a stress fracture is to decrease the stress on the bone which can be gauged by not having continued pain.  An endurance athlete can and should still cross-train (to maintain aerobic fitness) and use methods with less impact (i.e. swimming, cycling, pool running, elliptical, underwater or antigravity treadmills, etc.).  Treatment of each stress fracture is variable.  However, the longer an athlete had symptoms prior to diagnosis and treatment, the longer the recovery.  Females should also be evaluated for a calorie deficit relative to the level of training.  Besides eventually leading to a decrease in performance, insufficient calories causes irregular and/or decreased periods and impaired bone strength.

Phase One: Achieve a Pain-free State (generally lasting 2-6 weeks)

• Altered load to bone = rest: crutches, cast, walking boot, or normal walking without stress of training depending on pain level
• Symptom treatment: ice, acetaminophen (Tylenol) and cautious use of NSAIDs (i.e. ibuprofen, Advil, Motrin, Aleve)

Phase Two: Gradual Return to Full Training (usually introduced after pain-free for 1-2 weeks; generally lasting 2-6 weeks)

• Starting with lower impact activities such as biking and swimming eventually progressing through elliptical to treadmill to road running.
• If symptoms return, a decrease in activities will be required

Some sports medicine providers use pneumatic braces or bone stimulators to facilitate healing.  There is better evidence for the effectiveness of pneumatic braces for tibia stress fractures.

Prevention
The best treatment remains prevention.  Prevention of stress fractures starts with avoiding the number one cause—training errors such as excessive increase in volume and/or intensity.  In addition, the training load should match the level of conditioning (muscular endurance, muscular strength, and aerobic fitness).   Biomechanical factors should be addressed after any injury.  Orthotics may be indicated based on evaluation of your biomechanics.  Footwear should be changed every 300-350 miles.  Most importantly, listen to your body.  If you are having pain that does not go away, back down for a few days and allow your body to recovery.

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date: May 9, 2011