AJR 2005; 185:166-173
© American Roentgen Ray Society
MRI Findings of Femoral Diaphyseal Stress Injuries in Athletes
Bryan Hwang1,
Michael Fredericson2,
Christine B. Chung3,
Christopher F. Beaulieu1 and
Garry E. Gold1
1 Department of Radiology, Stanford University, Grant Building S0-60, 300
Pasteur Dr., Stanford, CA 94305-5105.
2 Department of Orthopedics, Stanford University, Stanford, CA.
3 Department of Radiology, University of California-San Diego, San Diego,
CA.
Received September 16, 2004;
accepted after revision October 29, 2004.
Address correspondence to G. E. Gold.
Introduction
Stress injuries of the bone result from excessive use and are
commonly seen in athletes, in whom the tibia, metatarsals, and femoral neck
are frequently involved. Although injuries of the femoral diaphysis are not
infrequent, the diagnosis often is delayed. Patients with these injuries
present with vague symptoms of anterior or medial thigh pain, and the injuries
often are initially misdiagnosed as muscle or tendon strains
[1]. In a retrospective study
of 320 athletes with stress fractures, the femoral shaft was the fourth most
common site of involvement, with an incidence of 7.2%
[2]. Early recognition of
pathology is critical to implementing a management regimen that prevents
progression of the injury and facilitates return to function and activity.
Given the relatively nonspecific clinical presentation, imaging plays a key
role in accurate and timely diagnosis. Although classic radiographic signs of
stress injuries have been described, they are insensitive
[2]. Radionuclide studies have
high sensitivity, but they are limited by relatively poor specificity and lack
of anatomic detail. MRI has emerged as the imaging technique of choice,
providing excellent sensitivity and specificity
[3,
4]. In this pictorial essay, we
present the spectrum of MRI findings seen with stress injuries of the femoral
diaphysis, with particular attention to a grading system that can aid the
clinician in designing a management plan tailored to each patient's specific
injury.
Pathophysiology
Stress injuries can be thought of as an exaggerated bone-remodeling
response to repetitive submaximal stresses, with osteoclastic activity
surpassing osteoblastic activity. This results in a net weakening of bone. It
is now well recognized that the development of a true stress fracture is the
final stage in this process in a continuum of preceding grades of injury.
Stress injuries involving the femoral diaphysis are less frequently
discussed in the literature than those involving the femoral neck or tibia
[5]. They occur with a
substantial prevalence, however, particularly in middle- and long-distance
runners. Although femoral shaft stress fractures can occur at any site along
the bone, the medial aspect of the proximal and middle thirds of the shaft
appears to be particularly susceptible. It has been suggested that this
predilection may relate to the biomechanical forces exerted on the bone during
weight bearing and muscle exertion
[4]. With weight bearing, the
medial aspect of the femoral shaft is under compression and the lateral aspect
is under tension. Although the degree of lateral strain may be partly reduced
by the action of the iliotibial tract and the vastus lateralis muscle, the
degree of medial compression force (and consequent stress on the bone) is
likely to increase with contraction of the vastus medialis and adductor longus
and brevis muscles. This model is borne out by our experience in evaluating
femoral stress injuries by MRI in a population of high-level runners. Most
injuries were preferentially located along the medial femur, in the proximal
and middle thirds of the shaft
[4].
An appreciation of this underlying pathophysiology has led clinicians to
view stress injuries as part of a continuum, with different management
approaches applied to each level of injury. MRI is very sensitive for
detecting early stress changes in bone and is specific for the severity of
injury [6]. In addition, the
lack of ionizing radiation in MRI is particularly advantageous in the
typically younger population evaluated for activity-related stress
injuries.
MRI Technique
Several MRI protocols can be implemented for imaging stress changes in
bone. At our institution, MRI is performed using a 1.5-T system (Signa, GE
Healthcare). Coronal and axial T1-weighted spin-echo sequences (TR/TE, 800/15)
and T2-weighted fast spin-spin-echo (4,000/54) with fat suppression are
performed in all studies. Imaging in the sagittal plane also is often done. A
widely used alternative to the fat-suppressed T2-weighted sequence is a STIR
sequence. The patient's area of worst pain is centered within the imaging
field when possible.
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Fig. 1A —18-year-old female long-distance runner who presented with
left thigh pain, worse with activity. Coronal T1-weighted image reveals no
gross abnormality and shows symmetric appearance of proximal femur.
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Fig. 1B —18-year-old female long-distance runner who presented with
left thigh pain, worse with activity. Fat-suppressed T2-weighted image clearly
reveals periosteal edema along medial aspect of proximal femoral shaft
(arrow). Allowing for slightly inhomogeneous fat suppression, the
marrow signal at this level is symmetric between the two femurs.
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MRI Grading of Injuries
A 5-stage MRI grading system that parallels a similar scintigraphic grading
system can be used to evaluate stress injuries of the bone. Previous reports
in the literature support the use of this grading system in directing
appropriate clinical management
[4,
7,
8].
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Fig. 2A —19-year-old female long distance runner who presented with
left hip pain. Coronal T1-weighted image of both hips shows only subtle
asymmetry of marrow signal in proximal subtrochanteric femurs.
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Fig. 2B —19-year-old female long distance runner who presented with
left hip pain. High-resolution T1-weighted image of left hip shows ill-defined
area of mildly decreased marrow signal (arrow).
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Fig. 2C —19-year-old female long distance runner who presented with
left hip pain. Fat-suppressed T2-weighted sequence is much more sensitive,
showing marrow edema predominantly along medial aspect of proximal diaphysis
(arrow).
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Grade zero represents a normal study. Grade 1 injuries show periosteal
edema that is subtle, even on fat-suppressed T2-weighted or STIR images (Figs.
1A,
1B,
1C, and
1D); this grade may correlate
with what also has been termed adductor insertion avulsion syndrome, or thigh
splint [6]. Grade 2 injuries
show periosteal edema and increased marrow signal on fat-suppressed
T2-weighted images (Figs. 2A,
2B,
2C,
2D,
2E,
2F, and
2G). Changes are subtle on
T1-weighted images, and they can be difficult to distinguish from hematopoetic
marrow. Grade 3 injuries show more extensive periosteal edema and marrow
signal abnormalities, readily seen on T1- and T2-weighted sequences (Figs.
3A,
3B,
3C,
3D, and
3E). Grade 4 injuries
represent progression to true stress fractures, with a discrete fracture line
visible on MRI (Figs. 4A,
4B,
4C,
4D,
4E,
4F,
5A,
5B,
5C, and
5D) or plain radiographs
(Figs. 5A,
5B,
5C, and
5D).
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Fig. 2D —19-year-old female long distance runner who presented with
left hip pain. Axial images of left femur confirm findings in A.
T2-weighted image also shows minimal medial periosteal signal abnormality
(arrows).
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Fig. 2E —19-year-old female long distance runner who presented with
left hip pain. Axial images of left femur confirm findings in A.
T2-weighted image also shows minimal medial periosteal signal abnormality
(arrows).
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Fig. 3A —19-year-old male long-distance runner who presented with left
leg pain. T1-weighted coronal image shows fairly extensive area of decreased
marrow signal in proximal femoral diaphysis. Medial cortical thickening at
this level reflects pathophysiology of stress injuries, with repetitive trauma
incurred over time (arrow).
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Fig. 3B —19-year-old male long-distance runner who presented with left
leg pain. T2-weighted image with fat suppression reveals marked periosteal
(arrow) and marrow edema. Increased signal is also noted within
cortex, but no discrete fracture line is appreciated.
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Fig. 3C —19-year-old male long-distance runner who presented with left
leg pain. Axial images show same findings (arrows). The medial side
of femur at junction between proximal and middle thirds of shaft is thought to
be particularly susceptible to stress injuries.
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Fig. 3D —19-year-old male long-distance runner who presented with left
leg pain. Axial images show same findings (arrows). The medial side
of femur at junction between proximal and middle thirds of shaft is thought to
be particularly susceptible to stress injuries.
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Fig. 3E —19-year-old male long-distance runner who presented with left
leg pain. T2-weighted image from follow-up study after conservative management
shows resolution of previous signal abnormalities. Patient was free of
symptoms at this time and had returned to normal activity levels.
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Fig. 4A —23-year-old female runner who presented with left hip pain
and decreased range of motion. Coronal T1-weighted image shows an area of
abnormally decreased marrow signal in proximal left femur, near level of
lesser trochanter. There is suggestion of discrete fracture line
(arrow).
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Fig. 4B —23-year-old female runner who presented with left hip pain
and decreased range of motion. Fat-suppressed T2-weighted image shows fracture
line to better advantage (arrow), recognized as linear low-signal
focus perpendicular to cortex, extending from medial surface into medullary
space. Surrounding marrow edema and associated joint effusion are also more
readily visualized.
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Fig. 5A —28-year-old male long-distance runner who presented with
right leg pain. Radiograph clearly shows fracture line in distal left femoral
shaft (arrows) with adjacent sclerotic change, consistent with grade
4 injury.
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Fig. 5B —28-year-old male long-distance runner who presented with
right leg pain. Radiograph clearly shows fracture line in distal left femoral
shaft (arrows) with adjacent sclerotic change, consistent with grade
4 injury.
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As expected, lower-grade injuries tend to have a faster and more
predictable course of recovery than higher-grade injuries. In fact, those with
low-grade injuries often can continue limited activity during the recovery
phase [7]. Higher-grade
injuries generally require longer non-weight-bearing periods of rest, and the
estimated time to return to activity is less predictable.
In conclusion, stress injuries to the bone fall along a continuum of
severity, with corresponding MRI findings that range from periosteal edema, to
marrow edema, to a true cortical fracture. These injuries systematically can
be graded based on these findings. In the femoral shaft, stress injuries often
elude diagnosis initially; therefore, imaging plays a central role in
diagnosis. Recognition and accurate grading of these injuries are critical for
optimizing clinical management of these patients, expediting a return to
activity.
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Introduction
Pathophysiology
