"Stress
Fractures in Female Athletes."
by Anne Z. Hoch
Stress fractures have two primary causes. They
result from excessive bone strain resulting in microdamage to
the bone coupled with an inability to keep up with appropriate
repair of the bone, or a depressed response to normal strain at
the cellular and molecular levels where bone remodeling occurs.
The former occurs most often in otherwise healthy female athletes
and military recruits, while the latter is likely to occur with
other physical problems, such as osteoporosis.
There were 2.4 million high school girls competing
in sports in 1997, an 800% increase over 1971. And stress fractures
occur more often in female athletes than male athletes. The risk
of stress fractures in female recruits in the US military is up
to 10 times higher than men undergoing the same training program.
There are many contributing factors to the greater
frequency of stress fractures in women. Male athletes may have
greater muscle mass, which absorbs shock better. In a study of
female athletes, decreased calf girth was a predictor of stress
fractures of the tibia. The larger width of male bones may also
absorb shock better.
Bone mass and bone mineral density can vary widely
in females due to several factors, including hormonal influences
and menstrual irregularities. Low calcium intake and eating disorders
may contribute to the development of stress fractures. Conversely,
oral contraceptive pills appear to help prevent stress fractures
in female athletes.
For both men and women, a rigid, high-arched
foot absorbs less stress and transmits greater force to the leg
bones, which may increase stress fracture risk. And studies of
female athletes have shown that having one leg slightly longer
than the other can increase the risk of stress fractures.
Other risk factors for stress fractures, in general,
include training regimen, footwear and training surface. For example,
higher weekly running mileage has been shown to correlate with
increased incidence of stress fractures. In another study, ballet
dancers who trained more than five hours a day had a significantly
higher risk of stress fractures than those who trained less than
five hours per day. A sudden change in frequency, duration or
intensity of training also affects the risk of stress fractures.
In addition, research has shown that training
in athletic shoes older than six months increased the risk for
stress fractures. Shoe age, rather than shoe cost, was a better
indicator of shock absorbing ability. In theory, training on uneven
surfaces, or hard surfaces like cement, could also increase stress
fracture risk. Female Athlete Triad
Stress fractures may be the first sign of a more
serious underlying condition, such as the "female
athlete triad." This is an inter-related problem consisting
of amenorrhea (no menstruation), disordered eating and osteoporosis,
a potentially lethal combination. Female athletes, particularly
those participating in individual sports, may feel significant
pressure to excel where leanness and a low body weight are seen
as advantageous.
Abnormal eating patterns include food restriction or fasting,
bingeing and purging, or the use of laxatives and diet pills.
In combination with decreased body weight and excessive training,
this can lead to menstrual disturbance, and in turn, low estrogen
levels. Women with disordered eating, estrogen deficiency and
menstrual dysfunction are predisposed to osteoporosis. Female
athlete triad sufferers are at a significant risk for stress fractures.
Several studies have shown that stress fractures
occur more commonly in women who have stopped menstruating or
have irregular periods than those who have a regular menstrual
cycle. Athletes with menstrual disturbances have lower estrogen
levels and this may lead to lower bone mineral densities. Estrogen
deprivation may affect the bone's ability to adapt to stress.
There is some evidence that beginning to menstruate
at a later age may be a factor in stress fractures. Another issue
for young female athletes is abnormally low levels of estrogen
and poor nutrition during adolescence. This can lead to lower
bone mass, which may be irreversible after a certain age.
Diagnosis and Treatment
A very specific and accurate diagnosis is the key to proper treatment.
Pain from a stress fracture of the neck of the femur (thigh bone),
for example, may cause pain in the groin, hip, front of the thigh
or the knee. Often standard X-rays do not disclose stress fractures.
A bone scan, CT (computerized tomography) scan or magnetic resonance
imaging may be more effective, depending on the site of the suspected
fracture. The pelvis, sacrum (in the lower back), and the femur
are areas where females tend to have a higher occurrence of stress
fractures. The patella (knee cap), tibia (shin bone), and bones
on the outside of the foot are other common areas of stress fractures,
the tibia being the most common of all.
The type of stress fracture and its location generally determine
treatment. In most cases, rest is the cure for stress fractures.
Non-weight-bearing exercise, such as swimming, may be prescribed
so that the athlete can maintain aerobic fitness. However, some
stress fractures require surgery to fix the bone in place so that
it can heal properly.
For more information, see "Stress Injury
to the Bone Among Women Athletes" in the November 2000 issue
of Physical Medicine and Rehabilitation Clinics of North America |
