Figure. Coronal magnetic resonance imaging of the lower extremities.
A 16-year-old girl presents to the office for evaluation of bilateral lower extremity pain that has gradually worsened over the past 2 months. She is on her cross country team and has been running 6 to 8 miles daily. She notes that her training has increased in intensity over the last 3 weeks due to an upcoming tournament. She states that she consumes a normal diet and has had a regular menstrual cycle for the past year. The patient takes an oral contraceptive to control her acne but does not take any other medication. A bone density test ordered by her primary care physician was normal. Coronal-view magnetic resonance imaging (Figure) is obtained and shows bilateral tibial stress fractures.
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Excessive endurance training in athletes can cause hormone imbalances and negatively affect the structural integrity of bones. Skeletal bone is constantly remodeled and repaired in response to increased stress placed during weight-bearing activities. Bone is resorbed in response to stress and replaced with new bone. A period of rest or removal of weight-bearing stress is critical to allow new bone formation.1
If repetitive stress is constantly placed on bone, microfractures may occur as bone formation lags behind resorption. Increasing endurance training can further damage bone and propagate stress fractures. Tibial shaft fractures pose a risk of fracture displacement if athletic activities continue. Patients with tibial shaft fractures should avoid sport participation for a minimum of 3 months; however, resolution of symptoms often takes 8 to 12 months of rest.2,3
Estrogen and testosterone are 2 hormones that influence bone remodeling. Estrogen slows bone resorption and helps maintain adequate bone density. Female athletes who participate in endurance sports such as long distance running are at risk for low estrogen levels and amenorrhea. Menstrual cycle changes can be influenced by exercise; running 10 miles per week has been shown to be associated with a 6% incidence of amenorrhea, and running 80 miles a week has a 43% incidence of amenorrhea.4
The patient in this case has a normal diet with normal caloric intake and a normal bone density test result, which most likely rule out low caloric intake, low estrogen levels, and metabolic bone disease as potential causes of the patient’s stress fractures.2,3
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor in chief of the Journal of Orthopedics for Physician Assistants.
1.Chen Y-T, Tenforde AS, Fredericson M. Update on stress fractures in female athletes: epidemiology, treatment, and prevention. Curr Rev Musculoskelet Med. 2013;6(2):173-181.
2. Tanaka MJ, Szymanski LM, Dale JL, Dixit S, Jones LC. Team approach: treatment of injuries in the female athlete: multidisciplinary considerations for women’s sports medicine programs. JBJS Rev. 2019;7(1):e7.
4. Voss LA, Fadale PD, Hulstyn MJ. Exercise-induced loss of bone density in athletes. J Am Acad Orthop Surg. 1998;6(6):349-357.