CHAPTER 66 • LOWER EXTREMITY STRESS FRACTURE 391osteoclastic activity that surpasses the rate of
osteoblastic new bone formation, resulting in tempo-
rary weakening of bone (Fredericson, Bergman, and
Matheson, 1997).- Whether stress fractures occur due to the increased
load after fatigue of supporting structures or are due to
contractile muscular forces acting across and on the
bone is debated; in principle, both factors contribute
(Daffner and Pavlov, 1992).
RISK FACTORS
- Most studies of stress injuries mention some alter-
ation in the training program as the most significant
factor in the production of injury. It has been well doc-
umented that there is an increased injury rate with
increasing distance beyond approximately 32 km per
week (Macera, 1992). - Also important is any rapid change in the training pro-
gram, whether a sudden increase in mileage, pace,
volume, or some other factor that has been inserted
into the program without adequte time for physiologic
adaptation to accommodate the new forces. Hard or
cambered training surfaces are also important precur-
sors to lower extremity overuse injuries (Fredericson
et al, 1995).
•Two independent anatomic variables were identified
as major risk factors for stress fracture: a narrow
transverse diameter of the tibial diaphysis and retro-
version (increased external rotation) of the hip.
Female runners with stress fractures were found to
have smaller calf circumference measurements.
Statistics suggest that women are at 1.5 to 3.5 times
greater risk for sustaining stress fractures than men
(Johnson, Weiss, and Wheeler, 1994).
HISTORY
- The typical history of a stress fracture is that of local-
ized pain that is not present at the start but occurs after
or toward the end of physical activity. This pattern is
opposite to that of many soft tissue injuries that have
pain first in the morning and with day to day activities
but reduced pain during physical activity. - The site of development of stress fractures varies from
sport to sport. Among track athletes, stress fractures
of the navicular, tibia, and metatarsal are the most
common; whereas in distance runners they can also be
seen in areas such as the femur or sacrum, although
stress fractures can involve any bone of the lower
extremity (Brunkner et al, 1996).
•A careful history often reveals some change in the
training regimen during the preceeding 2 to 6 weeks
and it is critical the physician ask detailed questions to
identify training errors as a cause.PHYSICAL EXAMINATION- The physical examination typically reveals local ten-
derness and swelling over the involved bone. Other
tests for the clinical detection of stress fracture such as
the hop test (femoral shaft) and fulcrum test and
spinal extension test (pars interarticularis) are helpful
but not as reliable as direct palpation (Johnson, Weiss,
and Wheeler, 1994). - As with the history, risk factors that can be detected
on physical examination should be evaluated. True leg
length discrepancies, femoral neck anteversion, varus
or valgus alignment at the knee, tibial torsion, muscle
weakness, excessive Q angle, and excessive subtalar
pronation or a pes cavus style foot should be noted
(Matheson et al, 1987).
IMAGING- In approximately two-thirds of symptomatic patients,
the radiographs are initially negative, and of these
only half ever develop positive radiographic findings
(Daffner and Pavlov, 1992). - The most common sign in early stress fracture is a
region of focal periosteal bone formation. The ‘‘gray
cortex’’ sign (a cortical area of decreased density) may
also be seen, and is an early sign of stress fracture
(Mulligan, 1995). - Radionuclide scanning is a more sensitive but less spe-
cific method for imaging bony stress injuries.
Radionuclide technetium-99 diphosphonate triple-phase
scanning can provide the diagnosis as early as 2 to 8
days after the onset of symptoms (Fredericson et al,
1995). - Magnetic resonance imaging(MRI) with fat suppres-
sion technique has shown promise in grading the pro-
gressive stages of stress fracture severity. A four-stage
grading system has been developed: A grade-1 injury
simply shows periosteal edema on the fat-suppressed
images. Grade-2, abnormal increased signal intensity is
seen on fat-suppressed T2-weighted images, and in
grade-3 injuries decreased signal intensity is seen on
T1-weighted images. In grade-4 injuries an actual frac-
ture line is present and is typically visualized on both
T1 and T2-weighted images (Fredericson et al, 1995). - MRI offers the advantages of multiplanar capability,
high sensitivity for pathology, ability to precisely