MRI is an extremely useful diagnostic tool for identifying suspected fractures in symptomatic patients with normal radiographs. The author reviews the utility of MRI for identifying two types of fracture: the truly “occult” injury and stress fractures.
MRI should be used in those situations in which a management decision must be made, when the patient’s employment depends on his or her ability to function, and in the “elite athlete.”
is a Professor of Radiologic Sciences, Drexel University School
of Medicine, Philadelphia, PA; and the Director of the Division
of Musculoskeletal, Trauma, and Emergency Radiology, Allegheny
General Hospital, Pittsburgh, PA.
The symptomatic patient with a suspected fracture and normal
radiographs challenges the diagnostic skills of clinicians and
radiologists alike. Magnetic resonance imaging (MRI) is the most
sensitive diagnostic tool for identifying fractures in their
earliest stages. This paper will review the utility of MRI for
identifying two types of fracture: the truly "occult" injury and
stress fractures. MRI should be used in those situations in which a
management decision must be made, when the patient's employment
depends on his or her ability to function, and in the "elite
The patient with a suspected fracture poses a challenge to the
clinician and to the radiologist alike. In most instances, there
are two common threads to this situation. First, there is a
symptomatic patient who has a history that suggests an injury and
physical findings that reinforce that assessment. Secondly,
however, any radio-graphs that are obtained are "normal." Under
most circumstances, prudent medical care dictates that the patient
be treated as if he or she had sustained a fracture. Follow-up
radiographs should be performed in 7 to 10 days, when they most
likely would show the fracture.
There is a subset, however, of patients in whom there is a "need
to know now" whether or not a fracture is present. Patients in this
category include those in whom a management decision needs to be
made immediately, those for whom their employment will depend on
their ability to perform their job, and finally, the "elite"
athlete. The first group is the most commonly encountered. In the
typical scenario, an elderly resident of a nursing home falls,
complains of hip pain, and cannot bear weight on the affected side.
Radiographs are obtained and are reported as showing no evidence of
fracture (Figure 1A). The dilemma facing the emergency department
physician is whether to admit the patient or to send him or her
back to the nursing home.
The second group includes the patient who sustains an injury to
an extremity that is used extensively in his job. Consider the case
of the right-handed heavy machinery operator who fell and complains
of wrist pain. His radiographs (Figure 2A) are reported as showing
no fracture. Should he be allowed to continue to use his right hand
The final group, the "elite" athletes, are either professional
athletes or key members of competitive college (or even high
school) teams. There is tremendous pressure from the coaches,
owners, parents, and players themselves for them to be allowed to
continue to play (Figure 3).
The solution for each of these clinical dilemmas may be found in
performing magnetic resonance imaging (MRI) on these patients. It
is well known that MRI is the most sensitive diagnostic tool for
identifying fractures in their earliest stages
(Figures 1B, 2B, and 3). In the ideal world, all patients with
suspected fractures would be studied emergently. However, in
today's environment of concerns for the costs of healthcare and
imaging studies, it is prudent to be highly selective in deciding
which patients are to be sent for MRI.
There are three areas for which MRI is most useful for the early
diagnosis of occult injuries: the hip, the wrist, and the sacrum.
Hip fractures are most likely to be suffered in an elderly,
osteopenic patient. The typical clinical scenario is as given above
and is one that is repeated on a daily basis in virtually all
emergency departments. In these instances, MRI may be the most
cost-effective study, since it can not only diagnose a fracture in
its earliest stage (Figures 1 and 4) but also can be used to rule
out a fracture or to find another cause of the patient's discomfort
(Figure 5). To facilitate evaluation of these patients, we have
developed a protocol for a limited MRI examination in the emergency
situation. Furthermore, we charge for a limited examination. We
typically perform coronal T1-weighted and short tau inversion
recovery (STIR) sequences. If these are normal, no further images
are obtained, and the patient is sent home. Some have advocated
using the coronal T1-weighted sequence alone, since it has a high
degree of sensitivity and specificity for finding an occult
On T1-weighted images, fractures appear as linear areas of low
signal; on STIR images these same areas will be of high signal
intensity, frequently surrounded by a zone of edema (Figure 4).
Similarly, occult fractures of other body parts may be studied in a
similar fashion, in the clinical setting where there is a "need to
know now" (Figure 3).
Stress fractures are common, but frequently overlooked, injuries
that are specific not only to the activities that produce them, but
also to location.
Two types of stress fracture are recognized: fatigue fractures,
which occur in normal bone placed under the stress of a new or
abnormal activity; and insufficiency fractures, which are the
result of normal activities on bones of abnormal or deficient bone
mineral. The clinical picture of a stress fracture should suggest
the diagnosis, if carefully analyzed. Typically, stress fractures
produce pain with activity that is relieved by rest. All other bone
lesions typically produce pain at rest or with activity and are
worse at night. Both lesions often respond to analgesics, and this
criterion cannot be used to confidently differentiate between the
The mechanics of stress fractures depend on muscle pull,
particularly from fatigue of opposing muscle groups. Since the
majority of most fatigue fractures occur in the lower limbs, poor
posture potentiates the effects of muscle pull. Furthermore, the
conditions of the activity, such as terrain and equipment, also
contribute to the development of stress fractures. For example, a
runner who typically runs on a gravel or grass track is more likely
to develop a stress fracture of one of the bones of the lower limbs
if he or she changes venue to pavement. In many athletes, a change
in brand of footwear will often result in stress fractures.
In most instances, the individual with a fatigue fracture will
cease the activity or seek medical advice, soon after the pain
begins. The elite athlete, however, faces both external and
internal pressure to continue in his or her endeavors for fear of
losing his or her position to another in the highly competitive
world in which they participate. There are definite hazards of
continued activity on bones that are undergoing stress fracture,
and radiologists should alert their clinical colleagues, trainers,
and coaches (if they see them) to these hazards. These risks
include: completing the fracture, distraction of the fragments,
fracture of another bone in the same limb, fracture of the same
bone in the opposite limb, progressive disability, and longer
Insufficiency fractures, on the other hand, typically occur in
older individuals, who don't fit the stereotype of the young
athlete. It is for this reason that clinicians frequently neglect
to ask their patients about any form of physical activity. Physical
fitness is now generally recognized as beneficial at any age, and
many older people are engaged in it. Mall walking is a popular form
of recreation, in which some shopping malls open their doors before
regular business hours to provide a safe, all-weather environment
in which to walk. Some of the larger malls may be one-half mile
from end to end. It is common on any given day to see large numbers
of people, mostly seniors, strolling at a brisk pace through the
Although osteopenia is the common denominator for the occurrence
of insufficiency fractures, previous irradiation is also a
contributing factor. Many patients with insufficiency fractures of
the sacrum and pelvis have a history of previous pelvic malignancy,
for which they received radiation therapy.
Unfortunately, such a history is likely to steer the clinician to
believing that the source for the pelvic or sacral pain is
metastatic disease, a decision that could have a deleterious effect
on the patient.
Imaging of stress fractures typically includes radiography,
radionuclide scanning, and MRI.
The radiographic findings will depend on the stage of the injury.
In the earliest stages, radio-graphs are likely to be normal. After
1 to 2 weeks, vague cortical lucencies and periosteal reaction will
be encountered. In later stages, callus and endosteal thickening
will occur. Stress fractures in elite athletes tend to be diagnosed
when the injury is fairly advanced, since they typically continue
in their endeavors despite the pain. However, patients with
insufficiency fractures often present to their primary care
physician or to the emergency department when they begin
experiencing pain. In these individuals, radiographs are typically
normal. Sacral insufficiency fractures are notorious for not
producing any radiographic changes. For these patients,
radionuclide imaging or MRI is performed. In most instances, a
positive bone scan is likely to result in an MRI being performed.
For this reason, I recommend MRI as the imaging procedure of choice
(assuming the radiographs are normal) (Figure 6).
The typical insufficiency fracture produces linear abnormalities
on both the radionuclide bone scan and MRI. In sacral insufficiency
fractures, the abnormalities are vertical as well as linear
(Figure 7). If bilateral sacral fractures are present, the
radionuclide pattern resembles the stylized "H" of the Honda logo
(Figure 8). The MRI signal changes due to any stress fracture are
the same as with any fracture, that is, decreased signal intensity
on T1-weighted images, increased signal intensity on T2-weighted
and STIR images, and enhancement with gadolinium (Figure 9).
Confirmation of a sacral insufficiency fracture should be with
computed tomography (CT).
It is important for the radiologist who suspects a stress
fracture to communicate this to the referring physician. More
importantly, the radiologist should emphasize the need to avoid
performing a biopsy on these lesions, since healing fractures can
be mistaken for osteosarcoma histologically.
MRI is an extremely useful diagnostic tool for identifying
suspected fractures in symptomatic patients with normal
radiographs. Two groups of injuries for which this modality is best
used are the "occult" fracture and stress fractures. In either
situation, a tailored, limited examination, consisting of
T1-weighted and STIR images can rapidly diagnose the fractures. In
addition, MRI is useful for identifying causes of the patient's
symptoms that are not due to fractures.