is Associate Professor of Radiology and Nuclear Medicine,
is Associate Professor of Radiology, and
is a Clinical Instructor at Louisiana State University Medical
Center in New Orleans, LA.
hen patients present with extreme pain following trauma to the
lower extremity and radiographs fail to demonstrate a specific
abnormality, MRI has been found to often be useful in establishing
the diagnosis. This article addresses specifically the use of MRI
in diagnosing intracapsular hip fractures, muscular injuries,
tibial plateau fractures, and injuries about the knee, as well as
stress fractures of the lower extremity.
Intracapsular hip fractures
MRI is an important modality in the detection of early hip
fractures when radiographs are inconclusive. The ability to
demonstrate intracapsular hip fractures at an early stage, prior to
displacement, is important because of the low association of
avascular necrosis with non-displaced fractures (figure 1). For
example, if a stage 1 garden fracture, or non-displaced fracture,
is allowed to progress to a stage 3 or 4 displaced fracture, it has
a significant chance of developing avascular necrosis of the
femoral head (figure 2).
Hip fractures are associated with incapacitation in more than
50% of patients. There is up to a 20% rate of mortality within one
year of such a fracture. In addition to considerable medical costs,
there also is tremendous psychological impact associated with these
fractures. A possible hip fracture should be suspected in patients
who present with severe hip pain and are unable to bear weight,
even when radiography fails to demonstrate an abnormality.
This can occur in young adults who develop stress fractures due to
overuse. More commonly, though, it occurs in the osteoporotic
postmenopausal woman due to insufficiency fractures. Our objective,
as radiologists, is to make the diagnosis soon after these
Limited sequence MRI is preferable to radionuclide bone
scintigraphy in diagnosing these fractures. By limiting the MR
sequences to long-axis coronal T1 images and a coronal STIR
sequence, the examination can be performed in under 10 minutes and
can be priced comparably to a radionuclide bone scan. Bone
scintigraphy may not demonstrate all fractures in healthy young
adults until 72 hours after the insult, and in elderly females it
may take as long as 5 to 7 days for fractures to be demonstrated.
However, uitlizing MRI, the marrow edema can be detected almost
immediately after the fracture occurs.
Muscular injuries and abnormalities
MR imaging is very sensitive to differences in water
distribution and can be useful in the detection of a variety of
muscle abnormalities secondary to muscle overuse and injury.
Acute muscle injury
--Muscular injuries which begin during activity and persist during
exercise are called strains and are secondary to violent muscular
contractions during forceful stretching. These injuries often are
seen in sports which require rapid acceleration. Strains most
commonly occur in muscles which cross two joints and are,
therefore, subject to stretching at more than one joint. These
injures are most often found at the musculotendinous junction and
most commonly occur during eccentric muscular contractions. Strains
are muscular tears, and are subdivided by grades which are
dependent upon the degree of muscular injury.
A grade I strain is a minor degree of tearing of the muscular
fibers. Patients with this type of strain recover without sequelae.
MR imaging will demonstrate an increased T2 signal, usually with a
feathery appearance and a slight increase in muscle size. Grade II
strains are partial tears of the muscle which result in loss of
strength. It may be difficult to differentiate grade I and grade II
strains on the basis of imaging alone. However, an identifiable
mass is more indicative of a grade II strain. Grade III strains are
full thickness muscle tears.
MRI detection of discontinuity of the muscle fibers or detection of
a gap with retraction of the edges and blood in the gap is
consistent with a grade III strain.
Acute direct muscle injury may occur secondary to penetrating or
non-penetrating trauma. A penetrating wound can result in
lacerations which may heal by scar formation.
Non-penetrating injuries cause contusion at the site of the
insult (figure 3). These injuries are characterized by tenderness,
diffuse swelling and, usually, a discrete hematoma.
The patient often presents with limitation of strength and motion.
These injuries are graded by the degree of severity as determined
by the extent of motion loss. For patients with mild injuries,
recovery usually takes less than one week. With moderate
contusions, motion is limited by one-third to
two-thirds of normal, with the disability lasting an average of 8
weeks. The quadriceps and the gastroc-nemious muscles are the most
commonly involved muscles.
It is important to differentiate an intermuscular from an
intramuscular hematoma as intramuscular hematomas are associated
with more complications and a longer recovery time. Additionally,
myositis ossificans may occur as a complication of muscular
contusions. If surgical biopsy or needle biopsy is performed early,
and if the biopsy is taken from the center of the lesion, pathology
could be confused with that of an osteosarcoma or a fibroscarcoma.
When radiographs are normal, an unusual cause of pain may be acute
myonecrosis of muscle secondary to cholesterol embolic infarction
Delayed onset muscle soreness (DOMS)
--Some individuals may experience severe muscular pain, swelling,
and stiffness following unaccustomed vigorous exercise or following
the resumption of training after a layoff. This is known as delayed
onset muscle soreness (DOMS). This pain is different from fatigue
which occurs during or immediately following exercise. Symptoms are
commonly localized at the musculotendinous junction and gradually
increase during the first 24 to 36 hours following the exercise.
Such symptoms are most severe in 2 to 5 days, and gradually
decrease in severity until they disappear, usually 7 to 10 days
following the initial event.
DOMS is similar to muscular strains in that muscles involved in
eccentric muscular action and those which cross two joints are most
commonly affected. Strains differ from DOMS in that strain
patient's symptoms develop immediately following the muscular
contractions during exercise, whereas DOMS has a quiescent period
of several hours before symptoms occur (figure 5). The injuries are
associated with prolonged T1 and T2 relaxation times of the
Chronic muscle disorders
--Patients with chronic muscular disorders can be differentiated
from those with normal muscle by the detection of fatty
infiltration or fatty replacement using standard imaging
Denervation is a known cause of muscle pain that may follow
trauma and manifest T2 prolongation on MR evaluation. If allowed to
progress, the muscle will atrophy and will be replaced by fat
MRI In the evaluation of knee fractures
Tibial plateau fracture
--Limited sequence long axis MR imaging of
the knee may detect fractures when the
radiographs fail to reveal any abnormality (figure 7).
In 1979, Schatzker
described six types of fractures of the tibial plateau; his
classification is the most commonly used among orthopedists and
radiologists today. Types of fractures in Schatzker's
classification include: Type 1, cleavage or wedge type fracture of
the lateral tibial plateau; Type 2, lateral wedge fracture with
adjacent depression; Type 3, pure central depression; Type 4, wedge
depression fracture of the medial plateau; Type 5, bicondylar
fracture of the tibial plateau; and Type 6, tibial plateau fracture
with disassociation of the metaphysis from the diaphysis.
Computerized tomography has for many years been the gold
standard in the diagnosis of these fractures.
To date, two studies have been performed to compare computerized
tomography to magnetic resonance imaging in this clinical scenario.
In 1994, a study by Kode et al for assessment of tibial plateau
fractures demonstrated that MR imaging was equivalent to CT in most
patients (specifically for fracture evaluation) and superior in
five patients. A total of 21 patients were evaluated under this
protocol. While CT was able to demonstrate and infer certain
soft-tissue injuries, MRI demonstrated meniscal injuries in 55%,
ACL tears in 27%, and complete collateral ligament tears in 53%.
In a study by Holt et al, 22 patients were evaluated, and
magnetic resonance imaging demonstrated a similar rate of
soft-tissue injury as CT imaging did. Additionally, MR was shown to
characterize fracture fragments and displacement, and to show
occult fractures, bone bruises, and internal derangements. These
injuries are not addressed specifically by the Schatzker
A common inference from these two independently-performed
studies is that MRI plays a significant role in assessment and
treatment planning of tibial plateau fractures, perhaps making it
the imaging modality of choice for suspected tibial plateau
fractures (figure 8). For some patients MRI will lead to
significant changes in their medical management and may reveal
reasons for treatment failure.
--A very common injury seen by MRI evaluation in patients with knee
trauma is a bone contusion or trabecular injury. This injury is
identified on MRI as a reticulated area of marrow exhibiting T1 and
It is important to recognize that the bone bruise itself is usually
painful and may be the cause of the patient's symptoms. In most
instances the pain subsides on its own, usually in 6 to 8 weeks.
In patients who have degenerative osteoarthrosis of the knee, a
horizontal cleavage tear is frequently seen, though it may be an
incidental finding. In patients with a horizontal cleavage tear
along with a bone bruise, the bone contusion is often the cause of
the patient's symptoms, and surgery is usually unnecessary in this
--MRI has an established role in diagnosing ACL injuries.
Deepening of the sulcus terminalis greater than 1.5 mm suggests a
torn ACL (figure 9). The presence of a SEGOND fracture, as well as
avulsion of the anterior tibia at the insertion of the ACL, also
may suggest the presence of an ACL tear.
Stress fractures of the lower extremity
Stress fractures occur as a result of repetitive prolonged
muscular action on bone and do not occur in non-weight-bearing
bones. The insufficiency fracture may occur with normal or
physiologic activity in a patient whose bones are deficient in
mineral or elastic resistance.
MR imaging has been valuable in defining the stages of a stress
fracture (figure 10). The earliest manifestation of a stress
fracture is the "stress response" which is due to bone marrow
If the causative action of the stress fracture is discontinued,
prevention of the cortical insult producing a fracture and the
proliferative periostitis may be prevented. The usual stress
fracture occurs perpendicular to the long axis of the bone and
occurs over a relatively short segment.
Longitudinal stress fractures are a much less common type of
stress fracture (figure 11). Patients with longitudinal stress
fractures of the tibia usually present with posterior medial tibial
pain. These fractures occur over a relatively long segment, and a
vertical fracture line may be seen on either MRI or CT.
As reported by Anderson recently, longitudinal stress fractures may
follow shin splints as a continuum of fatigue damage to bone.