AJR 2003; 181:191-194
© American Roentgen Ray Society
Collar Osteophytes: A Cause of False-Positive Findings in Bone Scans For Hip Fractures
Francisco Garcia-Morales1,
Gwy Suk Seo,
Vaseem Chengazi and
Johnny U. V. Monu
1 All authors: Department of Radiology, University of Rochester School of
Medicine and Dentistry, 601 Elmwood Ave., Box 648, Rochester, NY 14642.
Received May 13, 2002;
accepted after revision December 17, 2002.
Presented at the annual meeting of American Roentgen Ray Society, Seattle,
April—May 2001.
Address correspondence to J. U. V. Monu.
Abstract
OBJECTIVE. A retrospective review of our radiology database revealed
five elderly patients, seen over a 12-month period, whose findings were judged
positive for hip fractures on the basis of their bone scans, but whose MR
imaging findings were negative.
CONCLUSION. The presence of collar osteophytes around the femoral
neck caused a false diagnosis of hip fracture for these patients, as revealed
on radionuclide bone scans. CT or MR imaging correlation is needed where
collar osteophytes may have caused an incorrect diagnosis of hip fracture
based on a bone scan.
Introduction
Femoral neck fractures (loosely referred to as hip fractures) are a common
injury in the elderly. Quite often, findings on radiographs may be equivocal
or negative. The consequences of a missed hip fracture can be expensive to all
concerned. For this reason, bone scintigraphy, a sensitive method used to
detect bone abnormalities, has traditionally been used as an additional
imaging tool on elderly patients who present with hip pain with or without a
history of trauma, and who have negative or equivocal radiographic findings
for hip fracture [1]. MR
imaging has supplanted this role of scintigraphy in many centers, but bone
scintigraphy is still performed when MR imaging is not immediately available
or is contraindicated. Although bone scintigraphy is highly sensitive,
false-negative results can occur, and their causes are well documented in the
literature [2]. Also as a
result of the high sensitivity, false-positive results can occur and may lead
to unnecessary surgery for the patient. The occurrence of false-positive
scintigraphic findings in the diagnosis of hip fractures has received almost
no mention in the literature, and yet the effect can also be expensive for the
patient.
We present data from five patients seen in a 1-year period, in whom a bone
scan that revealed a collar or rim of osteophytes around the femoral neck led
to a false-positive diagnosis of hip fracture.
Materials and Methods
We searched our radiology database from a 12-month period for patients who
had bone scintigraphy for hip pain and in whom bone scintigraphy showed
results positive for hip fracture. From this group, we selected patients who
had negative radiographic and MR imaging findings obtained subsequent to the
bone scintigraphic study. Of 1840 bone scans obtained during this period, 70
were requested to investigate the cause of hip pain. Twenty-seven of the
studies were performed specifically to evaluate the hip for possible fracture.
Thirteen scans were rated positive for hip fractures. Five of these were
false-positive and form the subject for this report. The available
radiographs, bone scintigrams, MR images, and CT images from these five
patients were reviewed and correlated with the clinical information.
The radiographs included images of the pelvis and the index hip in frontal
and lateral projections. All bone scans were three-phase studies with the
patient lying supine under a double-headed gamma camera, either Biad (Trionix,
Twinsburg, OH) or Prism XP 2000 (Picker International, Cleveland, OH). Seven
hundred forty to 925 MBq of technetium-99m methylene diphosphonate was
administered IV, and images of the pelvis and both hips were obtained using a
low-energy all-purpose collimator at 4 sec per frame for 20 frames. Blood pool
images were obtained for 2 min at 5–10 min after injection of
radiopharmaceutical. Delayed 3-hr images were acquired in all patients to
allow soft-tissue clearance, and additional imaging using single-photon
emission computed tomography (SPECT) was performed on advice of the
radiologist. The SPECT images were routinely reconstructed and projected in
the axial, sagittal, and coronal planes using either a low-pass (Picker
International) or Hamming (Trionix) filter with the cutoff approximately 0.5
adjusted for study counts.
The MR imaging studies were performed on either of two Signa 1.5-T scanners
(General Electric Medical Systems, Milwaukee, WI) using a pelvic phased array
coil. Images were acquired in the oblique coronal plane using T1- and
T2-weighted conventional or fast spin-echo sequences with fat suppression.
Additional images were acquired in the axial plane using T2-weighted fast
spin-echo sequences with fat suppression. Our imaging parameters for
T1-weighted images were TR range/TE range, 600–700/8–12; field of
view, 16–24 cm; number of excitations, 1; matrix, 256 x 192. For
T2-weighted images, parameters were TR range/first-echo TE, second-echo TE,
2000–3000/80, 20; matrix, 256 x 192; number of excitations, 1. For
fast spin-echo images, parameters were effective TR range/TE range,
3500–4500/90–110; echo-train length, 6–12. Our slice
thickness for planes of imaging was usually 5 mm with an interslice gap of 1
mm. Contrast-enhanced coronal T1-weighted images with fat suppression were
also acquired in two patients.
The CT scans were obtained on one of three Hi-Speed CTI scanners (General
Electric Medical Systems) using a bone algorithm. The helical CT images were
obtained using a 1.5-mm collimation and a pitch of 1. Images were reformatted
at 3-mm slice thickness and displayed in both axial and coronal planes in bone
window settings.
Results
There were five patients, two men and three women, 65–79 years old,
with a mean age of 70.7 years. Three patients reported sudden onset of hip
pain, one patient indicated that pain had an insidious onset, and a fifth
patient gave a history of trauma 3–4 months earlier.
None of the patients had a history of recent or acute trauma. Two patients
had history of breast carcinoma and one had been treated for carcinoma of the
prostate. All patients had undergone radiography, bone scanning, and MR
imaging studies. Three patients had CT scans in addition. SPECT was used to
augment the regular bone scans in three patients.
The radiographs in all patients showed osteophytes around the femoral head
or neck (collar osteophytes) (Figs.
1A,
1B) or around the acetabular
lips (rim osteophytes) (Figs.
2A,
2B,
2C,
2D,
2E). The images generally
showed good bone mineralization, and no fractures were seen in the femoral
neck.
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Fig. 1A. —72-year-old woman seen at emergency department for acute
onset of left hip pain. MR images (not shown) did not indicate fracture. She
had hip replacement 6 months later for rapidly progressive osteoarthritis.
Frontal radiograph of left hip shows mild superolateral joint space narrowing,
and large osteophytes (arrowheads) are present around femoral
neck.
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Fig. 1B. —72-year-old woman seen at emergency department for acute
onset of left hip pain. MR images (not shown) did not indicate fracture. She
had hip replacement 6 months later for rapidly progressive osteoarthritis.
Technetium-99m bone scan image of pelvis (anterior view) shows linear
increased uptake (arrows) around left femoral neck simulating femoral
neck fracture.
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Fig. 2A. —65-year-old woman who was seen at emergency department for
acute exacerbation of hip pain with no history of acute trauma. She is being
followed up in rheumatology clinic for osteoarthritis. Lateral radiograph of
right hip shows large osteophytes around subcapital area of femoral neck
(arrows).
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Fig. 2B. —65-year-old woman who was seen at emergency department for
acute exacerbation of hip pain with no history of acute trauma. She is being
followed up in rheumatology clinic for osteoarthritis. Anterior view of pelvis
on technetium-99m bone scan shows band of increased uptake (arrows)
across femoral neck that is reminiscent of femoral neck fracture.
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Fig. 2C. —65-year-old woman who was seen at emergency department for
acute exacerbation of hip pain with no history of acute trauma. She is being
followed up in rheumatology clinic for osteoarthritis. CT image shows
osteophytes around femoral neck in greater detail.
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Fig. 2D. —65-year-old woman who was seen at emergency department for
acute exacerbation of hip pain with no history of acute trauma. She is being
followed up in rheumatology clinic for osteoarthritis. T1-weighted MR image
shows osteophytes (arrows) around femoral neck.
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Fig. 2E. —65-year-old woman who was seen at emergency department for
acute exacerbation of hip pain with no history of acute trauma. She is being
followed up in rheumatology clinic for osteoarthritis. Fat-saturated
T2-weighted MR image shows osteophytes (short arrow) around femoral
neck. Note large paralabral cyst (long arrow) seen as focus of high
signal at lateral aspect of hip.
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On bone scans, increased blood flow and blood pool was seen in the affected
hip in all the patients. All patients showed increased linear or bandlike
uptake in the subcapital or transcervical area in the affected hip (Figs.
1A,
1B,
2A,
2B,
2C,
2D,
2E,
3A,
3B,
3C,
3D,
3E,
3F). SPECT images (Figs.
3A,
3B,
3C,
3D,
3E,
3F) in three patients
confirmed the linear uptake traversing the femoral neck. The scintigraphic
findings in these five patients were judged to be compatible with occult
nondisplaced femoral neck fractures. All patients showed changes at other
sites that were considered degenerative.
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Fig. 3A. —72-year-old woman with known ostearthritis in right hip who
presented to emergency department with acute exacerbation of pain and
inability to bear weight on right hip. SPECT images were determined to be
compatible with femoral neck fracture. MR images did not show fracture.
Patient is still being followed up at our orthopedic clinic for
osteoarthritis. Radiograph shows narrowed hip joint space and subchondral
acetabular cyst, but no fracture. Note increased new bone along femoral
neck.
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Fig. 3B. —72-year-old woman with known ostearthritis in right hip who
presented to emergency department with acute exacerbation of pain and
inability to bear weight on right hip. SPECT images were determined to be
compatible with femoral neck fracture. MR images did not show fracture.
Patient is still being followed up at our orthopedic clinic for
osteoarthritis. Anterior image from technetium-99m bone scan shows increased
uptake (arrow) in right femoral neck suggesting fracture. Increased
uptake in acetabular roof is due to degenerative change.
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Fig. 3C. —72-year-old woman with known ostearthritis in right hip who
presented to emergency department with acute exacerbation of pain and
inability to bear weight on right hip. SPECT images were determined to be
compatible with femoral neck fracture. MR images did not show fracture.
Patient is still being followed up at our orthopedic clinic for
osteoarthritis. Selected image from series of SPECT images shows band of
increased uptake (arrows) across femoral neck.
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Fig. 3D. —72-year-old woman with known ostearthritis in right hip who
presented to emergency department with acute exacerbation of pain and
inability to bear weight on right hip. SPECT images were determined to be
compatible with femoral neck fracture. MR images did not show fracture.
Patient is still being followed up at our orthopedic clinic for
osteoarthritis. Another image from series of SPECT images (four slices from
C) reiterates continuous band of increased uptake (arrows)
across femoral neck, suggesting uptake traverses depth of femoral neck. This
was interpreted as nondisplaced femoral neck fracture.
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Fig. 3E. —72-year-old woman with known ostearthritis in right hip who
presented to emergency department with acute exacerbation of pain and
inability to bear weight on right hip. SPECT images were determined to be
compatible with femoral neck fracture. MR images did not show fracture.
Patient is still being followed up at our orthopedic clinic for
osteoarthritis. Coronal T1-weighted MR image shows osteophytes
(arrowhead) in femoral neck. No abnormal signals suggest femoral neck
fracture.
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Fig. 3F. —72-year-old woman with known ostearthritis in right hip who
presented to emergency department with acute exacerbation of pain and
inability to bear weight on right hip. SPECT images were determined to be
compatible with femoral neck fracture. MR images did not show fracture.
Patient is still being followed up at our orthopedic clinic for
osteoarthritis. Coronal contrast-enhanced fat-saturated T1-weighted MR image
shows enhancing subchondral cysts in acetabular roof (arrows)
corresponding to increased uptake on bone scans. T2-weighted MR images (not
shown) did not show femoral neck fracture.
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MR imaging studies were obtained after the hip radiographic and
scintigraphic studies. No fractures were found. Images showed large
osteophytes around the femoral head and loss of articular cartilage in all
patients (Figs. 2A,
2B,
2C,
2D,
2E). Three patients showed
signal changes suggesting bone marrow edema in areas away from the femoral
neck. Joint effusion was seen in three patients. One patient had a large
paralabral cyst (Figs. 2A,
2B,
2C,
2D,
2E).
Three patients had CT as part of their initial workup. The CT images showed
osteophytes around the femoral neck and acetabular lips (Figs.
2A,
2B,
2C,
2D,
2E), subchondral cysts, and
narrowed joint space.
Final diagnosis in all patients was osteoarthritis with exacerbation of hip
pain. The patients were treated successfully with nonsteroidal analgesics for
exacerbation of osteoarthritis. One patient had recurrent episodes and
underwent hip replacement surgery 3 months later for rapidly progressive
osteoarthritis of the hip.
Discussion
The literature indicates that bone scintigraphy has a high sensitivity
(97.8%) and specificity (95.0%) in the detection of occult fractures, with a
positive predictive value of 91.8% and a negative predictive value of 96.0%.
Although scintigraphy has shown special value in elderly patients with hip
pain and negative radiographic findings, our work suggests that false-positive
findings due to collar osteophytes may be relatively frequent in certain
populations [1,
3–5].
It has been well documented in the literature that false-negative findings can
occur, especially in elderly patients when scintigraphy is performed within 72
hr after trauma. This is likely because of slower bone turnover in this age
group [6]. The occurrence of
false-positive results has been less documented in the literature and has been
related to myositis ossificans or soft-tissue calcification, as in calcific
capsulitis, trochanteric bursitis, transient osteoporosis of the hip, and
active degenerative changes
[2]. Lewis et al.
[2] found that of the eight
cases with false-positive findings on bone scans in a series of 127 bone scans
positive for fractures, only one was due to the presence of collar
osteophytes. The apparent rate of false-positive fractures in the study of
Lewis et al. is lower than ours, which may be explained by a number of factors
including our patient selection, statistical anomaly due to our small numbers,
or even a low threshold for diagnosing fractures.
The implications of a false-positive bone scan could be serious because
femoral neck fractures often require emergency surgery with pinning or
hemiarthroplasty. These surgical procedures have some serious morbidity rates
and complications in this patient group. On the other hand, active and even
advanced osteoarthritis usually responds to medical therapy with nonsteroidal
antiinflammatory drugs, although some of these patients will later have
elective surgery.
Although bone scintigraphy has proven valuable in detecting occult hip
fractures in patients with negative radiographic findings, scintograms should
be interpreted with caution in the absence of osteopenia
[1–7].
Lewis et al. [2] were the first
to voice caution in the diagnosis of occult fracture in the presence of normal
bone mineralization and marginal osteophytes. No history of recent trauma
indicates other causes, such as exacerbation of osteoarthritis, to explain the
patient's symptoms. A reliable history may not be available for some elderly
patients, and additional imaging is warranted for proper diagnosis. MR imaging
is at least as sensitive as bone scintigraphy in the detection of hip
fractures [4,
8]. MR imaging has the
additional advantage of showing associated bone marrow edema, the fracture
line, and any other bone abnormalities such as osteophyte or subchondral cyst
formation, joint effusion, and loss of articular cartilage. Failure to
visualize a hip fracture has a 100% negative predictive value and makes this
diagnosis unlikely. When MR imaging is unavailable or contraindicated, CT is
another valuable imaging modality that can show fractures or degenerative
changes. Coronal reconstruction is recommended to avoid false-negative
findings, because axial imaging may in theory fail to reveal fractures
parallel to the axial imaging plane.
In conclusion, collar osteophytes are a cause of false-positive diagnoses
of hip fractures on radionuclide bone scans. Bone scans obtained for suspected
occult hip fracture should always be compared with radiographs. The presence
of osteophytes around the hip joint should prompt CT or MR imaging
correlation, if the bone scan appears positive for fracture of the femoral
neck.
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Abstract
Introduction
