DOI:10.2214/AJR.07.2513
AJR 2008; 190:1616-1620
© American Roentgen Ray Society
Stress-Related Injuries Around the Lesser Trochanter in Long-Distance Runners
Josephine T. Nguyen1,
Jeffrey S. Peterson2,
Sandip Biswal3,
Christopher F. Beaulieu3 and
Michael Fredericson4
1 Magnetic Resonance Imaging, Radiology, Long Beach Memorial Medical Center,
Long Beach, CA.
2 Innovative Sports Medicine, Mountain View, CA.
3 Department of Radiology, Stanford University Medical Center, Stanford,
CA.
4 Division of Physical Medicine and Rehabilitation, Department of Orthopaedic
Surgery, Stanford University Medical Center, 300 Pasteur Dr., Edwards Bldg.
R107A, Stanford, CA 94305-5336.
Received May 4, 2007;
accepted after revision December 4, 2007.
Address correspondence to M. Fredericson.
Abstract
OBJECTIVE. Imaging abnormalities around the lesser trochanter are
occasionally found in long-distance runners, yet little research has been
conducted concerning this area of the hip. In addition, the relation between
iliopsoas insertional abnormalities at the lesser trochanter and femoral neck
stress injuries has not been examined, to our knowledge. We report MRI
findings at the lesser trochanter in nine long-distance runners with hip or
groin pain and a consistent constellation of the following findings:
abnormalities associated with the iliopsoas tendon and its insertion,
including marrow edema at the lesser trochanter; periostitis around the lesser
trochanter; and bone marrow edema in the femoral neck. One case involved
temporal progression to a cortical fracture.
CONCLUSION. Long-distance runners with hip or groin pain and
abnormal MRI findings involving the insertion of the iliopsoas tendon and
marrow edema in the lesser trochanter may be at risk of stress injuries at the
femoral neck.
Keywords: femoral neck • iliopsoas • MRI • musculoskeletal • stress injuries
Introduction
Symptoms of groin or hip pain in long-distance runners can indicate
stress reactions at the femoral diaphysis or neck, but we are aware of only
one study [1] of the incidence
of injury at the lesser trochanter. Those investigators found this injury to
be quite common. The subjects were 71 athletes (89% of whom were runners with
hip, groin, or thigh pain) with 74 stress injuries to the femur. Using bone
scintigraphy, the authors detected abnormal radiotracer uptake isolated to the
lesser trochanter in 20% of the patients. MRI was not used in that study.
Bony stress injuries to the proximal femur can manifest with vague groin,
hip, or anterior thigh pain that worsens with continued weightbearing.
Physical examination is challenging owing to difficulty in palpating the
deeper bones in this area. The findings include limited range of motion of the
hip, pain on forced rotation or axial loading, and tenderness over the
involved bone, but these findings are nonspecific. A positive result of a hop
test, in which the patient reproduces the pain by hopping on the involved
extremity, occurs in as many as 70% of patients with femoral neck stress
fractures but also is not specific
[1]. The fulcrum test may help
in the early detection of femoral shaft stress fractures and in guiding
follow-up treatment [2].
Because of the limitations of physical examination, imaging is always
indicated when a patient has symptoms of stress injury to the hip joint.
Compared with radiography, bone scintigraphy, and CT, MRI is the most accurate
imaging technique for early diagnosis of bony stress injury
[3,
4]. MRI can help guide
management by defining the exact anatomic location and facilitating grading of
the degree of stress injury. For example, a stress injury to the femoral neck
with a cortical fracture necessitates abstention from weightbearing and close
monitoring for progression of the damage and the need for internal fixation
[5]. On the other hand,
isolated periostitis at the lesser trochanter or abnormalities limited to the
iliopsoas tendon may necessitate only a short period of modification of
activity. The aim of this study was to assess the MRI findings associated with
symptomatic stress injuries at the lesser trochanter in long-distance runners
to develop guidelines for clinical management.
Materials and Methods
Retrospective MRI evaluation was performed in the cases of nine
long-distance runners (seven women, two men; mean age, 28.8 years; range,
19-38 years) consecutively registered with MRI evidence of stress injury at
the lesser trochanter. All patients presented with anterior hip, thigh, or
groin pain aggravated by weightbearing activity. The pain had developed during
training for marathons or competition for club or university running teams.
The primary imaging criterion for inclusion in the study was bone marrow edema
at the lesser trochanter.
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Fig. 1 —36-year-old man with normal lesser trochanter. Axial
fat-suppressed T2-weighted MR image shows no decrease in marrow signal
intensity at lesser trochanter compared with elsewhere in medullary space.
Normal calcar femorale (arrow) should not be mistaken for a fracture
line.
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Fig. 2 —27-year-old man with normal lesser trochanter. Coronal
fat-suppressed T2-weighted MR image shows no decrease in marrow signal
intensity at lesser trochanter compared with elsewhere in medullary space.
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All patients underwent MRI with a 1.5-T system (Signa, GE Healthcare) and a
torso phasedarray coil. T1-weighted spin-echo imaging was performed at a TR of
800 milliseconds and a minimum TE, typically 15-18 milliseconds.
Fat-suppressed proton-density or T2-weighted imaging was performed at a TR/TE
of 4,000/54-72 and a matrix size of 512 x 192 for coronal images and 256
x 192 for axial images. Two signal averages were performed. The imaging
planes were coronal and axial; supplementary sagittal images were obtained in
some cases.
Each imaging study was evaluated by consensus by two board-certified
radiologists specialized in reading musculoskeletal MR images. The criteria
for a diagnosis of bone marrow edema were intramedullary low signal intensity
on T1-weighted images and intramedullary high signal intensity on T2-weighted
images that were significantly different from the surrounding signal intensity
in the medullary cavity. A fracture was diagnosed when a line of low signal
intensity was surrounded by abnormal signal intensity in the medullary cavity.
Periostitis was diagnosed when a thin band of high signal intensity was seen
adjacent to the cortex on T2-weighted images. Criteria for iliopsoas
insertional tendinopathy included thickening or abnormal signal intensity in
the tendon or abnormal signal intensity around the tendon.
MRI was performed at initial presentation of all patients. One patient, a
36-year-old woman who was a marathon runner, underwent follow-up MRI 6 weeks
after the initial study. She had not followed activity restrictions, and the
symptoms had worsened. The other patients did not need additional MRI; they
had followed treatment recommendations, and the symptoms had not
progressed.
Results
The following findings were seen in all patients: abnormalities associated
with the iliopsoas tendon at its insertion, periostitis near the lesser
trochanter, and varying degrees of marrow edema extending from the lesser
trochanter into the medial inferior aspect of the femoral neck
(Table 1). Examples of lesser
trochanters with normal MRI features are shown in Figures
1 and
2. The center of the lesser
trochanter was identified as a protuberance where the thick,
low-signal-intensity psoas tendon inserts. It is important to recognize that
at this level, a low-signal-intensity strut of bone projecting into the
medullary cavity represents the normal calcar femorale, which should not be
mistaken for a fracture line.
Bone marrow edema was represented by high signal intensity in the medullary
space of the lesser trochanter on fat-suppressed T2-weighted images (Figs.
3A,
3B,
3C,
3D,
3E,
3F,
3G,
3H,
4A,
4B and
4C). In all patients, varying
degrees of bone marrow edema extended to the medial inferior aspect of the
femoral neck immediately superior to the lesser trochanter. Periosteal
reaction at the lesser trochanter was represented by fluid signal intensity
along the periosteal surface of bone in this region (Figs.
3A,
3B,
3C,
3D,
3E,
3F,
3G,
3H,
4A,
4B and
4C). On long-T2-weighted
images abnormalities associated with the iliopsoas muscle and tendon included
thickening of the tendon and high signal intensity around the tendon at its
insertion on the lesser trochanter. This finding represented fluid or
soft-tissue edema at the enthesis (Figs.
3A,
3B,
3C,
3D,
3E,
3F,
3G,
3H,
4A,
4B and
4C).
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Fig. 3A —36-year-old woman marathon runner with groin pain after long
run. Coronal (A) and axial (B) T2-weighted fat-suppressed MR
images through lesser trochanter obtained at initial presentation show
thickening of right iliopsoas tendon and surrounding soft-tissue edema near
insertion of tendon on lesser trochanter (solid arrow) and marrow
edema at anterior aspect of lesser trochanter (dashed arrow,
A).
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Fig. 3B —36-year-old woman marathon runner with groin pain after long
run. Coronal (A) and axial (B) T2-weighted fat-suppressed MR
images through lesser trochanter obtained at initial presentation show
thickening of right iliopsoas tendon and surrounding soft-tissue edema near
insertion of tendon on lesser trochanter (solid arrow) and marrow
edema at anterior aspect of lesser trochanter (dashed arrow,
A).
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Fig. 3C —36-year-old woman marathon runner with groin pain after long
run. Coronal (C) and axial (D) T2-weighted MR images through
femoral neck obtained at initial presentation show soft-tissue edema
surrounding distal right iliopsoas tendon (straight solid arrow)
slightly proximal to its insertion and marrow edema extending to inferomedial
femoral neck (dashed arrow, C). High signal intensity
represents elevation of periosteum (curved arrow, D) off
cortex of inferomedial femoral neck.
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Fig. 3D —36-year-old woman marathon runner with groin pain after long
run. Coronal (C) and axial (D) T2-weighted MR images through
femoral neck obtained at initial presentation show soft-tissue edema
surrounding distal right iliopsoas tendon (straight solid arrow)
slightly proximal to its insertion and marrow edema extending to inferomedial
femoral neck (dashed arrow, C). High signal intensity
represents elevation of periosteum (curved arrow, D) off
cortex of inferomedial femoral neck.
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Fig. 3E —36-year-old woman marathon runner with groin pain after long
run. Two months after A-D, patient, who had not restricted
weightbearing, returned with worsened hip and groin pain. Coronal (E)
and axial (F) T2-weighted MR images show area of bone marrow edema in
right lesser trochanter (dashed arrow) has enlarged. Abnormal high
signal intensity of soft tissues surrounding iliopsoas tendon (solid
arrow) has progressed slightly.
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Fig. 3F —36-year-old woman marathon runner with groin pain after long
run. Two months after A-D, patient, who had not restricted
weightbearing, returned with worsened hip and groin pain. Coronal (E)
and axial (F) T2-weighted MR images show area of bone marrow edema in
right lesser trochanter (dashed arrow) has enlarged. Abnormal high
signal intensity of soft tissues surrounding iliopsoas tendon (solid
arrow) has progressed slightly.
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Fig. 3G —36-year-old woman marathon runner with groin pain after long
run. Coronal T2-weighted MR image shows small line of low signal intensity in
inferomedial femoral neck (dashed arrow) representing fracture line.
Abnormal high signal intensity of soft tissues surrounding iliopsoas tendon
(solid arrow) has progressed slightly.
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Fig. 3H —36-year-old woman marathon runner with groin pain after long
run. T2-weighted MR image shows abnormally high signal intensity of soft
tissues surrounding iliopsoas tendon (solid straight arrow) has
progressed slightly. Periosteal edema (curved arrow) is more
prominent than in D. Dashed arrow indicates line of low signal
intensity in inferomedial femoral neck.
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Fig. 4A —21-year-old man on university cross country team presented
after 2-week history of right hip pain, which had worsened since patient
stopped running. Three-phase bone scan (not shown) depicted increased uptake
at insertion of distal iliopsoas muscle and tendon. Coronal fat-suppressed
T2-weighted image shows marrow edema in lesser trochanter (solid
arrow) extending to inferomedial femoral neck (dashed
arrow).
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Fig. 4B —21-year-old man on university cross country team presented
after 2-week history of right hip pain, which had worsened since patient
stopped running. Three-phase bone scan (not shown) depicted increased uptake
at insertion of distal iliopsoas muscle and tendon. Axial fat-suppressed
T2-weighted images through lesser trochanter (B) and inferior femoral
neck (C) show marrow edema in lesser trochanter (dashed arrow,
B) and inferior femoral neck (dashed arrow, C),
thickening of iliopsoas tendon (solid arrow), and soft-tissue edema
surrounding tendon. Periosteal edema (arrowhead, B) is evident
along femoral neck and lesser trochanter.
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Fig. 4C —21-year-old man on university cross country team presented
after 2-week history of right hip pain, which had worsened since patient
stopped running. Three-phase bone scan (not shown) depicted increased uptake
at insertion of distal iliopsoas muscle and tendon. Axial fat-suppressed
T2-weighted images through lesser trochanter (B) and inferior femoral
neck (C) show marrow edema in lesser trochanter (dashed arrow,
B) and inferior femoral neck (dashed arrow, C),
thickening of iliopsoas tendon (solid arrow), and soft-tissue edema
surrounding tendon. Periosteal edema (arrowhead, B) is evident
along femoral neck and lesser trochanter.
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Three of nine patients had visible fracture lines. The lines were
approximately 1 cm long, extended slightly obliquely in the medial femoral
neck, and were visible on both T1- and T2-weighted images
(Fig. 3G). One patient had
follow-up imaging findings that showed progression from an initial
presentation of only marrow edema and iliopsoas insertion findings to cortical
fracture 6 weeks later (Figs.
3E,
3F,
3G and
3H). No patient had evidence
of bony avulsion of the lesser trochanter. In the cases of six of the patients
(seven sets of images), the contralateral asymptomatic hip was included in the
imaging field of view (Table
1). In none of these cases were abnormalities, such as
peritendinous edema or bone marrow edema, present around the contralateral
lesser trochanter.
Discussion
The most notable observation in the runners in this study was a consistent
constellation of findings that accompanied marrow edema at the lesser
trochanter: abnormalities associated with the iliopsoas tendon and its
insertion, including marrow edema at the lesser trochanter; periostitis around
the lesser trochanter; and bone marrow edema in the femoral neck. Each of
these findings in isolation is nonspecific and can occur in both stress
reactions and enthesopathy, hence the potential for confusing one diagnosis
for the other.
The enthesis is defined as the site of attachment of tendons and ligaments
to bone. It includes the adjacent inserting tendon, the periosteum, and the
bone at the attachment site
[6]. Periostitis occurs in
enthesopathy but also has been described as an early-grade bone stress
reaction at several sites in the body
[7,
8]. Bone marrow edema is often
found at many sites of tendon and ligamentous avulsion injury (enthesopathy)
[9,
10] but also occurs in stress
injury. Stress reactions are caused by undue stresses that lead to an
imbalance in bone remodeling, local osteopenia, and microfractures, which
manifest on MRI as bone marrow edema. Unchecked, this microscopic damage can
accumulate and result in a macroscopic fracture visible on MRI as a line of
low signal intensity [7,
8]. We believe that when these
abnormalities are found together, especially at the lesser trochanter, bony
stress injury should be suspected. The extension of marrow edema from the
lesser trochanter to the inferior medial femoral neck is particularly
worri-some for a femoral neck stress reaction.
It is important to differentiate iliopsoas insertional tendinopathy or
enthesopathy from a bone stress reaction because of the marked differences in
management. Initial therapy for musculotendinous injuries typically consists
of stretching, strengthening exercises, and in some cases, local
corticosteroid injection [11].
By contrast, protected weightbearing is indicated for bony stress injuries of
the femoral neck [12]. We
believe that in runners, the location of marrow edema at the lesser trochanter
signifies the earliest phase of a bony stress reaction and not merely
enthesopathy.
Several potential explanations exist for the tendency of iliopsoas
enthesopathy and femoral basocervical stress reactions to occur together in
runners. We postulate that during long-distance running, chronic traction
forces from the iliopsoas muscle, a powerful hip flexor, place undue stress on
the femoral neck [9,
10]. Endorsing this theory are
results with biomechanical models showing that contraction of the iliopsoas
muscle increases axial bending strain on the medial aspect of the femoral neck
to produce femoral neck fractures
[13,
14]. A second potential
mechanism involves decreased shielding of bone related to muscle fatigue. With
extensive training or long runs, muscle fatigue is thought to result in more
load transmission to bone, thereby increasing the risk of osseous injury
[15,
16]. Because musculotendinous
units are prone to injury, the iliopsoas musculotendinous unit can be injured
by repetitive, excessive, or unbalanced contraction of the iliopsoas muscle
during running [17]. The
flexor musculotendinous unit acts as a shock-absorbing spring during running
[18], and injury to this
structure can expose the femoral neck to injury during running, especially at
push-off. Injury to the tendon near its insertion can cause reactive marrow
edema at the lesser trochanter and place forces at the inferomedial femoral
neck that expose this site to stress injury, giving rise to the constellation
of findings found in our patients.
That findings at the lesser trochanter can precede a stress fracture of the
inferomedial femoral neck is supported by the visualization of temporal
progression to a stress fracture in one patient who did not follow
recommendations for activity restriction and had worsening of symptoms, for
which follow-up imaging was performed. The relation to femoral neck fracture
is further suggested by identification of two other patients who had a
fracture line in the medial femoral neck. Although these patients did not have
previous images to show temporal progression from findings isolated to the
lesser trochanter from a femoral neck fracture, femoral neck fracture was
shown to coexist with other abnormalities at the lesser trochanter, as for
other patients in this series.
In previously devised MRI-based schemes for grading bone stress injury, the
sole presence of periostitis is assigned grade 1. The addition of bone marrow
edema constitutes grades 2 and 3, depending on severity. The presence of a
fracture line without displacement constitutes grade 4. To our knowledge, such
a grading system has been applied to the femoral shaft
[4,
7,
8] and tibial shaft
[7] but not to the lesser
trochanter or basocervical femoral neck fracture. On the basis of the findings
in our limited case series, we recommend that patients with evidence of marrow
edema (grade 2 and greater) in the lesser trochanter be treated as if they
have a stress injury and be required to refrain from any running or impact
activities until symptoms subside. If there is any significant extension of
the edema into the inferior femoral neck, the patient should be treated with a
period of protected weightbearing and close monitoring for assessment of
progression.
Stress injuries are increasing in frequency owing to the increasing
popularity of marathon training and other endurance sports. Because MRI can
show subtle periosteal edema, marrow edema, and fracture lines not seen on
radiographs, MRI is probably the most valuable tool for detecting symptomatic
stress reactions in distance runners. Although it is well known that early
stress injuries can progress to frank fractures, to our knowledge, such
progression around the lesser trochanter has not been previously documented.
The potential relation between abnormalities at the lesser trochanter and
basocervical femoral neck stress fractures has not been previously described,
to our knowledge. We conclude that abnormalities at the lesser trochanter can
indicate impending femoral neck stress injury in runners. Conservative
treatment recommendations are indicated along with a period of activity
restriction and possibly protected weightbearing.
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Abstract
Introduction
