Stress fractures represent 4 to 16 percent of running injuries.1 Fractures occur in 8 percent of the males and 13 percent of the females.1 The cause of stress fractures is repetitive and sub-maximal loading of the bone. The bone eventually fatigues and a stress fracture occurs. Prolonged stress can lead to a complete fracture. A regular fracture differs from a stress fracture in that no acute trauma has taken place.
Endurance events, like marathons and Ironman triathlons, expose the bones in the foot to increased stress and strains in these endurance events. When training for these endurance events, the ground reaction forces can approach 3½ to 12 times body weight. Bone geometry and bone density influence how we respond to these ground reaction forces. When it comes to endurance athletics, certain bones react differently to the stress placed upon them. For example, long bones are more resistant to compression forces but seem to have more problems with torsional or bending forces.2,3
Approximately 500,000 marathon times were recorded in 2010.4 This represents a 6.4 percent increase for males and a 10 percent increase for females. Women represent an increasing number of marathon finishers. Forty-two percent of all marathon finishers were female.4
There was an even larger increase in half marathons in 2011. The constant influx of amateur athletes means that sports injuries are on the rise as well. Another endurance event has shown recent growth. The Ironman triathlon consists of a 2.4-mile swim, an 112-mile bike ride and a 26.2-mile run. It is an elite endurance event differing from other triathlons by its extreme distance.
Training for these extreme athletic events exposes the endurance athlete to repetitive lower extremity trauma due to ground reactive forces. The many hours required to be prepared for such events set up the athlete for a multitude of possible problems with injuries.
High-level physical activity can cause well-documented hormonal changes in females. Consider the female athlete triad of eating disorders, amenorrhea and osteoporosis. Osteoporosis is related to a decreased rate of estrogen, which may lead to lower mineral absorption in bone and possible stress fractures due to poor bone density.Women who have zero to five menses a year have a 49 percent higher risk of stress fracture.6 Those with more menses demonstrated a lower rate.
Testosterone may have a direct effect on bone formation by influencing the osteoblasts.6 Long-term exercise may suppress baseline levels, thus affecting bone structure. Several studies have reported lower bone density in male long-distance runners. Male triathletes have also shown significantly lower levels of testosterone.6
The relationship of prolonged exercise on the male athlete causing stress fractures is not well understood. It may be related to hormonal control but may not be as significant as it is to female athletes.6
Vitamin D is a fat soluble vitamin. When our dermal layers absorb ultraviolet rays from sunlight, this triggers the synthesis of vitamin D. The vitamin is inert and must undergo hydroxylation in the body. Vitamin D promotes calcium absorption in the gut and maintains serum calcium and phosphate concentration to enable normal mineralization of the bone.
In one study, female military recruits who took calcium and vitamin D had a 20 percent lower incidence of stress fracture.7 Stress fractures are one of the most common injuries in female recruits.
Plain radiographs are the first option for evaluating stress fractures. Unfortunately, the sensitivity may be low. X-rays are positive only 33 percent of the time for navicular stress fractures.8,9 Often, it takes up to three weeks to visualize the stress fracture when bone callus and bone resorption occur.
A bone scan is almost 100 percent diagnostic for stress fracture but a positive result can indicate other issues as well.8,9 Magnetic resonance imaging (MRI) is also good for detecting stress fractures and can also help with soft tissue injuries. Computed tomography (CT) scans may be the best imaging technology for certain stress fractures but it is important to do 1.5 mm cuts so one does not miss the fracture.8,9
Rest is always the best option for treating stress fractures. The amount of rest varies upon location of the fracture, severity, the strength of the body’s healing response and nutrition. One should cast a stress fracture for four to eight weeks at a minimum.10 However, 12 to 16 weeks may be required for certain fractures and certain bones. Returning to activity depends on pain and the amount of healing the doctor perceives.
Treatment starts with no weightbearing for certain high-risk stress fractures and may progress to weightbearing as tolerated. The athlete’s activities may progress to non-weightbearing activities, such as swimming. This progresses to partial weightbearing activities like riding on a spin bike with low resistance at first and progressing to higher resistance, and standing with time. Eventually, patients can use an elliptical trainer and finally do full weightbearing exercises. Once runners are clear for activity, they should increase their mileage by 10 percent a week and start with softer surfaces like soft groomed trails and tracks.
Using a below the knee cast for treatment of stress fractures can be very beneficial since it redistributes weight and decreases motion at the fracture site. Using an air cast also may be helpful. It puts light pressure on the bone, increasing blood flow to the area to assist in the healing. Control of swelling caused by the fracture should begin as soon as possible to prevent prolonged healing. Anti-inflammatories may also be helpful.
Another key component of treatment is the custom orthotic device. Functional orthotics can help control subtalar pronation. Use of these devices can decrease the vector forces through the foot, which can alleviate some of the weightbearing forces. Orthotics can also redistribute the weight equally throughout the foot, keeping extra pressure off the fracture site. Studies have shown that orthotics not only treat but can prevent lower extremity stress fractures. In a study involving military recruits, Finestone, Milgrom and their respective colleagues showed that orthotics can lower the incidence of stress fractures to 10 to 15 percent in comparison to 27 percent without them.10,11
Other treatment considerations would include but are not limited to nutrition, vitamin therapy, running surfaces, avoiding a large cant in the road, shoe therapy, body mass index, gravity and quality of training, hormonal therapy, age, race genetics, calorie intake and calcium levels.2,4
High-risk stress fractures include the anterior cortex of the tibia and medial malleolus, the navicular, and the base of the second and fifth metatarsals. Low-risk fractures include the fibula, calcaneus and the metatarsal shafts. More aggressive treatment is required for high-risk fractures. One should consider treatments such as additional rest, casting, non-weightbearing and possibly surgery.3
Endurance athletes have the advantage of Wolff’s law of mechanical stress. The more pressure that goes through a bone, the more the forces will align the bone resistance to any fracture force by strengthening its cortices. Muscle strengthening also helps stabilize the bone to resist fractures as well.
Endurance athletes represent a unique subset of athletes due to their high volume of training and racing. There are many advantages to their extreme training but there are also some physiological disadvantages. By understanding the risk factors of training, endurance athletes can hopefully avoid some of the pitfalls of their sport, including stress fractures.
Dr. Mozena is in private practice at the Town Center Foot Clinic in Portland, Ore. He is a Fellow of the American College of Foot and Ankle Surgeons, and is board certified in foot and ankle surgery. Dr. Mozena is an Associate Clinical Professor at the Western University of Health Sciences in Pomona, Calif. He has completed six Ironman triathlons, 14 half-Ironman triathlons and over 20 marathons, including the Boston Marathon.
1. James BH, Thacker SB, et al. Prevention of lower extremity stress fracture in athletes and soldiers: a systematic review. Epioemiol Rev. 2002; 24(2):228-247.
2. Reeser JC, Lorenzo CT. Physical medicine and rehabilitation for stress fracture. Emedicine. Available at www.Medscape.com/article/309106  .
3. Martinex JM, Calhoun JH. Stress fracture. Emedicine. Available at www.Medscape.com/article/1270244 .
4. USA Marathon. 2010 overview. Available at http://usamarathontraining.com/#  .
5. Barrow GW Saha, S. Menstrual irregularity and stress fractures in collegiate female distance runners. Am J Sports Med. 1998; 16(3):209-16.
6. Bennell KL, Brukner PD, Malcolm SA. Effect of altered reproductive function and lowered testosterone levels on bone density in male endurance athletes. Br J Sports Med. 1996; 30(3):205-208.
7. Institute of Medicine of the National Academies. Dietary Reference Intakes for Calcium and Vitamin D. Available at http://www.iom.edu/Reports/2010/Dietary-Reference-Intakes-for-Calcium-an...  .
8. Coris EE, Lombardo JA. Tarsal navicular stress fracture. American Family Physician. 2003; 67(1):85-91.
9. Saxena A, Cassidy A. Secrets to treating stress fractures of the ankle. Podiatry Today. 2002; 15(6):38-45.
10. Finestone A, Giladi M, Elad H. Prevention of stress fractures using custom biomechanical shoe orthoses. Clin Orthop. 1999; (360):182-90.
11. Milgrom C, Giladi M, Kashtan H. A prospective study of the effect of a shock-absorbing orthotic device on the incidence of stress fractures in military recruits. Foot Ankle. 1985; 6(2):101-4.
For further reading, see “Treatment Tips For Common Triathlon Injuries” in the October 2002 issue of Podiatry Today.