Patterns of Occult Hip Fractures and Mimics Revealed by MRI

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AJR:182, February 2004 283

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.

AJR

2004;182:283–288

0361–803X/04/1822–283

© American Roentgen Ray Society

H



284

AJR:182, February 2004

Oka and Monu

tions. The radiographs were reviewed for adequacy

of the image quality and the presence of fractures.

A study was deemed adequate when the acetabu-

lum, femoral head, and femoral neck were visual-

ized on two images. No patients were excluded

because of inadequate radiographs.

Sixty-four of the 76 MRIs of the hip were ob-

tained within 48 hr after the radiographs. However,the interval between radiographs and MRI studies

ranged from 5 days to 3 weeks in the other 12 cases.

All MRI studies were performed on a 1.5-T unit

(Signa, General Electric Medical Systems, Milwau-

kee, WI) using a commercially available pelvic

phased array surface coil as a receiver. Imaging pro-

tocols varied but generally included T1-weighted

spin-echo images (TR/TE range, 600/14–18; slice

thickness, 5 mm; interslice gap, 0.5–1.0 mm; matrix,

256 ×

192) in the axial and oblique coronal planes;

T2-weighted fast spin-echo images (TR range/TE

range, 3,200–5,000/96–102; slice thickness, 5 mm;

interslice gap, 0.5–1.0 mm; matrix, 256 ×

192) with

fat saturation; and occasional STIR images (TR/TE,

4,800/60; inversion time, 150 msec; slice thickness, 5

mm; interslice gap, 0.5–1.0 mm; matrix, 256 × 192)

in the coronal or axial plane. Images in the sagittal

plane using dual-echo spin-echo pulse sequences

were infrequently obtained. Field of view ranged be-

tween 16 and 22 cm to cover the index hip joint.

The MRIs were evaluated for the presence and

site of bone or soft-tissue injury. The bone injuries

were characterized as bone contusion or fracture.

A fracture was diagnosed when a linear low-

signal focus was surrounded by an intermediate-

signal area on T1-weighted images and the linear

low-signal focus was surrounded by high signal on

T2-weighted images [9, 10, 12]. Ill-defined areas

of altered signal intensity on T1-weighted images

and high signal intensity on T2-weighted images

were interpreted as bone marrow edema.

Soft-tissue injuries were further characterized

as muscle edema, hematoma, partial muscle tear,

or complete muscle tear using criteria that have

been previously defined [13–19].Acute muscle injuries have associated edema and

hemorrhage that cause prolongation of the T1 and T2

relaxation times of the injured tissue [14]. Muscle in-

juries were diagnosed when areas of increased signal

intensity were seen on T2-weighted or STIR images.

Complete tears showed total disruption of the muscle,

muscle retraction, blood, and edema in the tear. A par-

tial tear is seen as a focal interruption of continuity of

the muscle without complete transection of the mus-

cle or tendon. Muscle edema was seen as a nongeo-

graphic area or an infiltrative pattern of low signal on

T1-weighted and high signal on T2-weighted images

that could not be distinguished from early interstitial

hemorrhage. Any confined area of altered signal

within or outside the muscle fibers was identified as a

hematoma, which is a form of muscle injury [13, 14].

In a setting of trauma, it may be difficult to differenti-

ate an isolated hematoma from a hematoma arising

from a muscle injury; a hematoma was therefore con-

sidered to be muscle injury in this study. A hematoma

may show varying signal intensities on both T1- and

T2-weighted images, depending on the evolving state

of hemoglobin [20].

We further analyzed our results in terms of

muscle function and stratified the muscles around

the hip joint into groups as follows: thigh adduc-

tor, thigh abductor, external rotator, internal rota-

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



MRI of Hip Fractures


285

In the innominate bones, there were five ace-

tabular fractures and 13 fractures of the obtura-

tor ring. Two patients had bone marrow edema

without focal cortical disruption (Fig. 2).

In the group with fractures on MRI, 24

(69%) had associated muscle injury. The obtu-

rator externus muscle, a major external rotator,

was abnormal in 15 studies (43%). Injury to

the other external rotators of the hip, which in-

clude the gluteus maximus, piriformis, obtura-

torius internus, gemelli, and quadratus

femoris, was seen in 17 studies (49%). Injury

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 ).

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Oka and Monu

to the thigh adductor was seen in 22 studies

(63%). In this group of patients with adductor

muscle injuries, five (23%) were associated

with femoral fractures and 17 (77%) were re-

lated to fractures of the innominate bone.

On the basis of MRI findings, 41 patients

(56%) did not have a fracture. Twenty-six

(63%) of the patients in this group had muscle

injuries. The obturator externus muscle was the

most frequently injured muscle, with abnormal-

ity seen in 13 (32%) of the 41 patients (Fig. 3).

Injury to the other external rotators of the hip

was seen in 14 studies (34%). Twelve studies

(29%) showed injuries in the abductor group(Tables 2 and 3 and Appendix 1).

Trauma was the indication for the study in

42 patients (58%), including 27 (77%) of the

35 studies showing fractures and 15 (37%) of

the 41 studies showing no fracture. The re-

maining 31 patients (43%) had pain but no

history of recent trauma, and the study was

requested to consider unexpected fractures.

Among these patients were eight fractures

(26%) and 13 muscle injuries (42%).

Overall, muscle injuries were seen in 50

studies (66%). Muscle edema, hemorrhage,

and partial tear represented most of the muscle

injuries and were seen in 49 studies. One pa-

tient had an iliopsoas muscle abscess (Fig. 4).

Mean patient age was 70 years in the fracture

group and 63 years in the nonfracture group.

The distribution of abnormalities detected in

individual muscles and in various functional

muscle groups is shown in Appendix 1 and Ta-

ble 2. Injury to the gluteus medius and gluteus

minimus, which are strong internal rotators of

the hip and thigh abductors, was seen with

equal frequency in patients with and withoutfractures. Injury to the gluteus maximus was

more frequently seen in patients without frac-

ture. The external rotators are the most com-

monly injured muscles in both groups.

Fifteen patients (21%) (13 women and

two men) had no fractures or muscle injuries

on MRI. The mean age in this group was

57.3 years (range, 33–81 years).

Discussion

The term “hip fracture” implies a proximal

femoral fracture, usually involving the femoral

neck. Proximal femoral fractures involving thefemoral neck or intertrochanteric regions are

devastating injuries to the hip that need to be

promptly diagnosed. However, injuries that in-

volve the innominate bone or adjacent muscles

may present with similar signs and symptoms.

In this series, 24% of the studies showed pel-

vic fractures that were occult on radiography,

with fractures of the obturator ring (21%) be-

ing the most common.

Generally, patients who sustain obturator

ring fractures or muscle injury around the

hip joint do not require surgery; however,

they can still have prolonged immobilization,

difficulty with ambulation as a result of pain,

and subsequent impaired hip function if the

fracture is not properly treated. Physical

therapy and early mobilization are essential

for these patients to recover as much func-

tion as possible.

Muscle injuries were present in 65% (49/

76) of studies regardless of the presence or

absence of fracture. Muscle injury may be

caused by a direct blow (contusion) or an in-

direct injury (strain due to abnormal stretch-

ing) and may result in edema, hemorrhage,

muscle tear, and hematoma. Edema and

hemorrhage present as high signal intensity

interspersed in muscles on T2-weighted im-

ages. In this series, the adductor muscle

group was frequently injured in association

with an obturator ring fracture.

Muscle tears tend to occur at or near the

musculotendinous junction and are seen as

focal high signal intensity on T2-weighted

images. Moderate strain and partial tears are

difficult to distinguish from hemorrhage

when the latter are located near the junction.

MRI may not always differentiate between a

muscle strain or tear that is associated with a

fracture and hemorrhage into the muscles

from a fracture. MRI findings reflect only the

relative presence of edema, deoxyhemoglo-

bin, and methemoglobin (Fig. 5).

The frequency and distribution of muscleinjuries were similar in the group of patients

with fractures (69%) and in the group with

no bone injuries (63%). Some of the ob-

served clinical signs and symptoms are

caused by associated muscle injuries [11].

The 46% occult fracture rate in this study is

similar to a fracture rate of 54% in the study by

Bogost et al. [11]. The differences in our fig-

ures may be partly explained by the fact that

Bogost et al. studied only patients with a clear

history of trauma. Because a clear history of

trauma may not be readily available in elderly

patients, we included in our study population

patients with a clinically suspected hip fracturewith no history of trauma. Our position is sup-

ported by the subsequent observation that

nearly 23% (35 patients) of the fractures were

in our group of patients who did not recall or

give a clear history of trauma.

In addition to obturator ring fractures,

Bogost et al. [11] reported a small number of

sacral fractures. We found no sacral fractures

in our study population. The sacrum was not

TABLE 2 Muscle Injury, by Individual Muscles (n = 76)

Muscle No Fracture (n = 41) Fracture (n = 35) Total (n = 76)

Iliopsoas 5 5 10

Obturator internus 3 7 10

Obturator externus 13 15 28

Pectineus 3 5 8Adductor longus 6 7 13

Adductor brevis 7 10 17

Adductor magnus 7 5 12

Gluteus minimus 7 8 15

Gluteus medius 7 6 13

Gluteus maximus 6 3 9

Tensor fasciae latae 1 1

Rectus femoris 2 2

Vastus lateralis 2 2

Piriformis 2 2

TABLE 3Muscle Injury, by MuscleGroup (n = 76)

Muscle GroupNo Fracture

(n = 41)

Fracture

(n = 35)

Extensors 11 8

Flexors 5 5

Adductors 7 12

Abductors 11 9

Internal rotators 13 14

External rotators 17 19



MRI of Hip Fractures


287

routinely included in our images because our

imaging protocol called for a smaller field of

view. The incidence of muscle injury in our

study population was similar to that of Bogost

et al., which was 61% (40% in the fracture

group and 21% in the no-fracture group).

The elderly patient is generally fragile and

does not require a major traumatic event to

sustain a fracture or significant muscle in-

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 ).



288


Oka and Monu

for MRI of the hip varied during the study pe-

riod. However, our entire patient population had

both T1-weighted and T2-weighted sequences

as part of their study. Although multiple radiolo-

gists interpreted the conventional radiographs,

our retrospective review showed that no frac-

tures were missed on radiographs.

In conclusion, soft-tissue injuries com-

monly accompany hip fractures but may exist

in isolation and may mimic fractures in that

they can produce similar symptoms. Soft-tis-

sue injuries alone can be a cause of morbidity

and merit additional attention. MRI is useful in

the diagnosis of soft-tissue injuries, especially

in the setting of clinically suspected hip frac-

tures. MRI is recommended for all symptom-

atic patients whose conventional radiographs

do not reveal a hip fracture.

References

1. Rudman N, McIlmail D. Emergency department

evaluation and treatment of hip and thigh injuries.

Emerg Med Clin North Am

2000;18:29–66

2. Lu-Yao GL, Keller RB, Littenberg B, Wennberg

JE. Outcomes after displaced fractures of the

femoral neck: a meta-analysis of one hundred and

six published reports. J Bone Joint Surg Am

1994;76:15–25

3. Schultz E, Miller TT, Boruchov SD, Schmell EB,

Toledano B. Incomplete intertrochanteric frac-

tures: imaging features and clinical management.

Radiology

1999;211:237–240

4. Ganel A, Engel J, Oster Z, et al. Bone scanning in

assessment of fractures of the scaphoid. J Hand

Surg

1979;4:540–543

5. Matin P. Bone scintigraphy in the diagnosis and

management of traumatic injury. Semin Nucl Med

1983;13:104–122

6. Grainger C, Garcia J, Howart NR, May M, Rosier

P. Role of MRI in the diagnosis of insufficiency

fractures of the sacrum and acetabular roof. Skel-

etal Radiol

1997;26:517–524

7. Haramati N, Staron RB, Barax C, Feldman F. Mag-

netic resonance imaging of occult fractures of the

proximal femur. Skeletal Radiol 1994;23:19–22

8. Rubin SJ, Marquardt JD, Gottlieb RH, Meyers

SP, Totterman SMS, O’Mara RE. Magnetic reso-

nance imaging: a cost-effective alternative to

bone scintigraphy in the evaluation of patients

with suspected hip fractures. Skeletal Radiol

1998;27:199–204

9. Quinn SF, McCarthy JL. Prospective evaluation

of patients with suspected hip fracture and inde-

terminate radiographs: use of T1-weighted MR

images. Radiology

1993;187:469–471

10. Deutsch AL, Mink JH, Waxman AD. Occult frac-

tures of the proximal femur: MR imaging. Radi-

ology

1989;170:113–6

11. Bogost GA, Lizerbram EK, Crues JV III. MR im-

aging in evaluation of suspected hip fracture: fre-

quency of unsuspected bone and soft-tissue

injury. Radiology

1995;197:263–267

12. May DA, Purins JL, Smith DK. MR imaging of

occult traumatic fractures and muscular injuries

of the hip and pelvis in elderly patients. AJR

1996;166:1075–1078

13. Kneeland JB. MR imaging of sports injuries of the hip.

Magn Reson Imaging Clin N Am 1999;7:105–115

14. El-Khoury GY, Brandser EA, Kathol MH, Tearse

DS, Callaghan JJ. Imaging of muscle injuries.

Skeletal Radiol 1996;25:3–11

15. De Smet AA. MR imaging of acute and remote

muscle injuries. In: De Smet AA, ed. Musculoskele-

tal MRI: normal anatomy and key pathology

.

(ARRS categorical course syllabus) Leesburg, VA:

American Roentgen Ray Society, 2001:97–103

16. Deutsch AL, Mink JH. Magnetic resonance imag-

ing of musculoskeletal injuries. Radiol Clin North

Am

1989;27:983–1002

17. Palmer WE, Kuong SJ, Elmadbouh HM. MR imag-

ing of myotendinous strain. AJR

1999;173:703–709

18. De Smet AA. Magnetic resonance findings in skele-

tal muscle tears. Skeletal Radiol

1993;22:479–484

19. Arrington ED, Miller MD. Skeletal muscle inju-

ries. Orthop Clin North Am 1995;26:411–422

20. Bush CH. The magnetic resonance imaging of

musculoskeletal hemorrhage. Skeletal Radiol

2000;29:1–9

21. Warwick R, Williams PL.

Gray’s anatomy

, 35th

ed. Edinburgh, Scotland: Longman Group,

1973:559–571

22. Pandey R, McNally E, Ali A, Bulstrode C. The

role of MRI in the diagnosis of occult hip frac-

tures. Injury

1998;29:61–63

23. Rizzo PF, Gould ES, Lyden JP, Asnis SE. Diagno-

sis of occult fractures about the hip: magnetic res-

onance imaging compared with bone scanning.

J

Bone Joint Surg Am

1994;75:395–401

24. Mlinek EJ, Clark KC, Walker CW. Limited mag-

netic resonance imaging in the diagnosis of occult

hip fractures. Am J Emerg Med 1998;16:390–392

APPENDIX 1. Functional Muscle Groups About the Hip

Extensors

Primary:

Gluteus maximus, adductor magnus

Other:

Gluteus medius, gluteus minimus, biceps femoris, semitendinosus,

semimembranosus

Flexors

Primary:

Iliopsoas, pectineus, sartorius, tensor fasciae latae

Other:

Adductors, rectus femoris

Adductors

Primary:

Adductor longus, adductor brevis, adductor magnus, gracilis

Other:

Obturator externus, pectineus, gluteus maximus

Abductors

Primary:

Gluteus medius, gluteus minimus, tensor fasciae latae, sartorius

Other:

Piriformis, quadratus femoris

Internal Rotators

Primary:

Gluteus medius, gluteus minimus, tensor fasciae latae, pectineus

Other:

Semitendinosus, semimembranosus

External Rotators

Primary:

Gluteus maximus, piriformis, obturator internus, obturator externus,

superior gemellus, inferior gemellus, quadratus femoris

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Patterns of Occult Hip Fractures and Mimics Revealed by MRI