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8/3/2019 Patterns of Occult Hip Fractures and Mimics Revealed by MRI
Prevalence and Patterns of OccultHip Fractures and Mimics Revealedby MRI
OBJECTIVE.
The diagnosis of hip fractures can be difficult on radiography alone. MRI is
frequently used to confirm or deny the presence of a minimally displaced hip fracture. This
study evaluates the patterns of injury seen on MRI that are difficult to diagnose on radiography.
MATERIALS AND METHODS. MRIs of 73 patients who were examined for possible
hip fractures and whose radiographic findings were negative or equivocal for hip fracture
were reviewed. Seventy-six studies were performed in 73 patients who were between 24 and
102 years old. MRIs were evaluated for the presence and location of bone or soft-tissue injury.Muscle injuries were categorized on the basis of location and type of injury.
RESULTS.
Forty-six percent (35/76) of the studies showed subtle fractures. Seventeen
fractures were in the proximal femur and 18 in the innominate bone. Soft-tissue abnormali-
ties were common, found in 65% of the studies. Twenty percent of the MRI findings were
considered normal because there was no apparent finding on the images to explain the pa-
tients’ symptoms.
CONCLUSION.
Soft-tissue abnormalities are commonly seen alone or in association
with subtle fractures on MRI in the evaluation of patients with a clinical suspicion of hip frac-
ture. MRI is recommended for all symptomatic patients whose radiographic findings are neg-
ative for hip fracture.
ip injury is a growing medical prob-
lem, mostly because of an increasein the elderly population and in
high-velocity motor vehicle trauma affecting
young people [1]. Prompt and early diagnosis is
important in minimally displaced fractures of the
femoral neck because delayed diagnosis and
treatment may result in significant displacement
of the fracture fragment [2]. Significant displace-
ment will alter the treatment and require more
extensive surgery, such as hemiarthroplasty in-
stead of stabilization with internal fixation.
Diagnosis of minimally displaced hip frac-
tures on radiographs can be challenging, es-
pecially in elderly patients with osteoporosis
[3–7]. In these patients, in the face of reason-able clinical suspicion for fracture, MRI is
recommended for further evaluation when
conventional radiographic findings are nega-
tive or equivocal [7–10].
A subset of patients exist who have clini-
cal signs and symptoms of hip fracture but
do not show a fracture on MRI. Various soft-
tissue injuries have been found on MRI of
some of these patients [11, 12].
Evaluating the incidence and type of bone
and muscle injuries in cases of clinical suspicionof hip fracture will help clarify injury patterns
that clinically mimic femoral neck fractures.
Materials and Methods
Patients with a clinical suspicion of hip fracture
who underwent MRI of the hip because radio-
graphic findings were reported to be negative were
retrospectively identified from our radiology data-
base. Seventy-six studies from 73 patients—28
men and 45 women—satisfied the selection crite-
ria and form the population of this study. One pa-
tient was evaluated for bilateral hip fractures, and
one patient with systemic lupus erythematosus
who was undergoing steroid therapy was evaluatedon three occasions. The patients were 24–102
years old (average, 67 years).
All images were reviewed in conference by both
authors, one a fellowship-trained and experienced
musculoskeletal radiologist and the other a trainee
radiologist. Except for three patients who were
evaluated with only frontal radiography of the pel-
vis, all patients underwent radiography of the pel-
vis in the anteroposterior projection and of the hip
in anteroposterior and cross-table lateral projec-
Mayumi Oka
1,2
Johnny U. V. Monu
1
Received April 5, 2002; accepted after revisionAugust 19, 2003.
Presented at the 2001 annual meeting of the American
Roentgen Ray Society, Seattle, WA.
1
Department of Radiology, University of Rochester Schoolof Medicine and Dentistry, University of RochesterMedical Center, 601 Elmwood Ave., Box 648, Rochester, NY14642. Address correspondence to J. U. V. Monu.
2
Present address: Department of Radiology, JohnsHopkins Hospital, 600 N Wolfe St., Baltimore, MD 21287.
tor, flexor, and extensor. This stratification was
based on their primary function or function when
the hip was in a neutral position [21]. The individ-
ual muscles and the functional muscle groups are
shown in Appendix 1.
Results
Our retrospective review showed that no
fractures were missed on radiographs.
Thirty-five (46%) of 76 studies were found
to have fractures on MRI (Table 1). The frac-
tures were four fractures of the greater tro-
chanter (Fig. 1), five intertrochanteric
fractures, and eight femoral neck fractures.
TABLE 1Fractures and Locations(n = 35)
Fracture Location No.
Femoral fractures
Neck 8
Intertrochanteric 5
Greater trochanteric 4
Total 17
Pelvic fractures
Pubic rami alone 13
Acetabulum alone 2
Pubic rami and acetabulum 3
Total 18
Grand total 35
Fig. 1.—77-year-old woman with fracture of greater trochanter after fall. Fracture was difficult to visualize on conventional radiographs.A, Frontal radiograph of left hip appears to show normal findings.B, T1-weighted coronal image of left hip shows linear low-signal focus (arrowheads ), indicating fracture.
BA
8/3/2019 Patterns of Occult Hip Fractures and Mimics Revealed by MRI
Fig. 2.—67-year-old woman who presented with persistent right hip pain after fall 3 weeks earlier.
A, Frontal radiograph of right hip shows unremarkable findings.B, Coronal T2-weighted image shows abnormally high signal in anterior column of hip and in area of superior pubic ramus, consistent with trabecular fracture. Linear ab-normally high signal is seen in adductors and obturator externus and is compatible with presence of interstitial edema or hemorrhage.
BA
Fig. 3.—73-year-old man who experienced hip pain after fall. He had no fractures, but MRI showed muscle injury.A, T1-weighted coronal image shows abnormal signal of interstitial muscle hemorrhage (arrows ) in obturator externus muscle near its attachment to greater trochanterand in musculotendinous junction.B, T2-weighted coronal image shows abnormal signal in obturator externus muscle near its attachment to greater trochanter and in musculotendinous junction. Thesefindings are compatible with interstitial hemorrhage (arrows ).
BA
8/3/2019 Patterns of Occult Hip Fractures and Mimics Revealed by MRI
jury. A history of trauma may not be readilyavailable or recalled. Furthermore, hip frac-
tures in the elderly may present with atypical
symptoms, such as several weeks of pain or
gait instability. Occasionally in this popula-
tion, some nontraumatic causes of hip pain
such as an iliopsoas abscess (Fig. 4) and
even exacerbation of hip arthritis may
present acutely and mimic a hip fracture.
Frequently, these elderly patients have coex-
isting morbidity that confuses the clinical
picture and confounds accurate diagnosis.
Because morbidity and mortality after hip
injury in the elderly have a significant socio-
economic impact, prompt and accurate diag-nosis is imperative [1].
MRI not only facilitates the diagnosis of
nondisplaced fractures not seen on radio-
graphs [8, 10, 22, 23] but also provides infor-
mation that may be beneficial for the
appropriate treatment of other injuries. Lim-
ited MRI protocols with T1-weighted coro-
nal images were previously reported to be
sufficient to detect proximal femoral frac-
tures [9, 24]. However, we emphasize the
usefulness of T2-weighted sequences in the
diagnosis of injuries other than hip fractures.
T2-weighted images facilitate recognition of
soft-tissue injuries. In addition, areas of bone
marrow edema cannot be distinguished from
sclerosis using T1-weighted images alone.
The main limitation of this study is that it
was retrospective. The study population was too
small for statistical confirmation. The protocols
BA
Fig. 4.—81-year-old woman with abscess in iliopsoas muscle who presented with left hip pain, no history of trauma, and clinical suspicion of occult fracture.A, T1-weighted axial image shows rounded low-signal focus (arrow ) adjacent to left iliacus muscle.B, T2-weighted image shows central area of high signal surrounded by concentric focus of low- and high-signal zones, consistent with abscess (solid arrow ). Abnormallyhigh signal in iliacus muscle (open arrows ) is result of muscle inflammation.
Fig. 5.—74-year-old woman with iliopsoas avulsion injury after fall 2 days before MRI examination. T2-weightedaxial fast spin-echo fat-suppressed image shows abnormally high signal (arrows ) in and surrounding iliopsoasmuscle, which is consistent with partial tear of muscle and surrounding hemorrhage. Note also some abnormalsignal around gluteus minimus muscle (asterisks ).
8/3/2019 Patterns of Occult Hip Fractures and Mimics Revealed by MRI