AJR 2005; 184:1470-1474
© American Roentgen Ray Society
16-MDCT in the Detection of Occult Wrist Fractures: A Comparison with Skeletal Scintigraphy
Ashley M. Groves1,
Heok Cheow2,
Kottekkattu Balan2,
Helen Courtney1,
Philip Bearcroft1 and
Adrian Dixon1
1 Department of Radiology, Addenbrooke's Hospital NHS Trust and the University
of Cambridge, Box 218, Hills Rd, Cambridge CB2 2QQ, England.
2 Department of Nuclear Medicine, Addenbrooke's Hospital NHS Trust and the
University of Cambridge, Cambridge, England.
Received April 4, 2004;
accepted after revision August 12, 2004.
Address correspondence to A. M. Groves.
Abstract
OBJECTIVE. Our objective was to assess the potential use of MDCT in
the detection of occult scaphoid fractures. Fifty-one patients with suspected
radiographically occult scaphoid fractures at 10–14 days after trauma
were investigated prospectively with skeletal scintigraphy and CT on the same
day. Planar images of the wrist were taken 3 hr after IV injection of 400 MBq
of 99mTc-methylene diphosphonate using a single-head gamma camera.
CT was performed on a 16-MDCT machine using 0.75-mm detectors and
reconstruction in 0.5-mm slices. Multiplanar reformatted images were then
viewed in interactive cine mode. The examinations were reported independently,
and discordant results were compared at follow-up. CT was positive for wrist
fracture in 14 (27.4%) of 51 patients and skeletal scintigraphy in 23 (45.1%)
of 51 patients. Even after retrospective review, there were seven discrepant
cases (13.7%), all of which were positive for wrist fracture on scintigraphy
but negative on CT. Four of these seven patients with discordant findings
underwent further radiography at 6 weeks, which did not show fracture.
CONCLUSION. Although CT was preferred by most patients and was
quicker, scintigraphy appears to detect bony abnormality more frequently.
However, there appears to be an interesting group of patients (7/51) with
normal initial radiography findings but positive scintigraphy findings who
would normally be considered to have a fracture but for whom CT results were
negative. In some of these patients, the results of follow-up radiography at 6
weeks were also negative, suggesting that this group of patients warrants
further study.
Introduction
The scaphoid is the most common carpal bone to be fractured
[1]. However, the incidence,
mechanism, natural history, and treatment of such fractures remain
controversial [1]. The fracture
must be identified early, as immediate treatment is required to minimize the
chances of nonunion and avascular necrosis, thereby avoiding disability.
Clinical examination is unreliable for making the diagnosis
[2]. Furthermore, radiography,
although it can be useful [3]
and is considered by some investigators to be sufficient in excluding fracture
[4], in practice lacks
sensitivity for diagnosis of undisplaced scaphoid fractures
[5]. Consequently, many other
imaging methods have been used. Conventional 99mTc-methylene
diphosphonate (99mTc-MDP) skeletal scintigraphy is widely used for
the detection of radiologically occult scaphoid fractures when clinical
suspicion of fracture is high
[6]. In an attempt to enhance
fracture detection and localization further, SPECT
[7] with
radiographic–scintigraphic image coregistration has been used with some
success [8,
9]. Newer techniques such as CT
have been helpful in scaphoid trauma
[10,
11], and MRI appears to be
particularly useful
[12–14].
Some institutions use MRI as a primary investigation in the emergency
department for suspected radiologically occult wrist fracture
[15]. Other approaches, such
as dynamic gadolinium-enhanced perfusion MRI
[16] and sonography
[17], have also been tried.
Ironically, a return to radiographic techniques has also been attempted
recently, with impressive results
[18].
Conventional CT has certain inherent advantages for examination of
high-attenuation tissue such as bone. Moreover, the recent advent of
multidetector technology has revolutionized the CT technique. The tiny 0.75-mm
detectors allow thin-section, multiplanar reconstructions from isometric
voxels at subminute examination times
[19]. These advances have
increased the versatility of CT and improved visualization of bone cortex and
trabecula patterns. For these reasons, we performed a prospective study
comparing 16-MDCT and conventional skeletal scintigraphy.
Subjects and Methods
Over a 12-month period, 51 patients (17 male and 34 female; age range,
17–81 years; mean, 40.2 years) presenting to the nuclear medicine
department for investigation of suspected wrist fracture underwent 16-MDCT on
the same day as scintigraphy. All patients had presented to the trauma center
of the hospital at the time of injury, and all had undergone wrist radiography
(four views). The radiographs were interpreted routinely by the duty
radiologist, and no fracture was detected. Ten to 14 days later, the patients
underwent follow-up radiography, which also failed to detect a fracture. Then,
one of three trauma physicians requested scintigraphy and indicated the
clinical probability of fracture (high, medium, or low) based on the
individual subjective diagnostic certainty. At the end of both studies,
patients were asked to complete a short questionnaire (in an either/or format)
indicating whether they preferred CT or scintigraphy.
Scintigraphy was performed using IV injection of 400 MBq of
99mTc-MDP. Planar images of the wrists (including the entire hand
and distal half of the forearm) were obtained 3 hr after the injection. Images
were acquired by a single-head gamma camera using a high-resolution collimator
and 800,000 counts per image. The images were then displayed on a 128 x
128 matrix. The images were interpreted routinely by the duty nuclear
physicians, who included an experienced nuclear medicine specialist along with
a senior nuclear medicine trainee, without knowledge of the CT findings.
CT was performed on a 16-MDCT machine using a Somatom Sensation 16
(Siemens). The wrist was imaged from the radiocarpal joint (including 1 cm of
distal radius) to the metacarpal phalangeal joints. CT images were acquired
using the 0.75-mm detectors and the images were reconstructed in 0.5-mm
increments. The table feed was 12 mm per rotation. The length of the CT
examination was recorded. The images were displayed on a proprietary
workstation (Siemens) using a high-spatial-frequency algorithm. Multiplanar
reformatted images were then viewed in interactive cine mode. Images were
viewed not only in axial, coronal, or sagittal planes but also, when
necessary, as oblique planar reconstructions on the workstation. The CT
studies were interpreted, by consensus, by an experienced musculoskeletal
radiologist and a senior trainee specializing in CT, neither of whom knew the
nuclear medicine findings. A fracture was diagnosed when a cortical breech was
deemed present. When consensus could not be reached, the opinion of the senior
radiologist was accepted.
A single experienced nuclear medicine physician and a single experienced CT
radiologist then retrospectively reviewed discordant cases. At that time, the
findings of initial and repeated imaging and of clinical examination were made
available.
All patients in our series gave informed consent before participating in
the study. The project was approved by the local ethics committee.
Despite retrospective review and follow-up, sensitivity and specificity
figures were not quoted because there is no universally accepted gold standard
for diagnosing wrist fracture.
A chi-square test (with Yates correction) was performed to compare the
imaging findings with the probability of fracture as determined clinically by
the referring doctor. In calculating this probability, we used only cases with
a high or low probability and only those for which the CT and scintigraphic
findings were concordant.
Results
At the initial, masked, interpretation, 23 fractures were diagnosed on
scintigraphy and 14 on CT. The sites of the fractures as diagnosed on both
scintigraphy and CT are summarized in Table
1. After the masked interpretation, 11 cases were discordant.
These included one case positive on CT and negative on scintigraphy and 10
cases negative on CT and positive on scintigraphy.
On review of the discordant cases, one showed increased tracer uptake in
the pisiform on scintigraphy that was not identified on the initial
interpretation. In another case, a trapezium fracture was not identified
initially on CT. One patient had a fracture identified on scintigraphy that
was outside the CT field of view (radius). In one further case of fracture,
the scintigraphy findings were confirmed on both MRI and 6-week follow-up
radiography.
After review, seven cases (13.7%) remained discrepant, all of which were
positive on scintigraphy but negative on CT. CT showed no evidence of
soft-tissue induration in any of these cases. Four of the patients with
discordant findings underwent further radiography at 6 weeks. In all four, no
radiographic evidence of fracture remained. Four of the patients with
discordant findings showed degenerative disease on CT (Fig.
1A,
1B), and this degeneration also
was seen on the radiographs of two.
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Fig. 1B. —56-year-old woman with persistent wrist pain after fall.
Coronal CT reconstruction of wrist shows severe arthropathy causing difficulty
in identifying fracture. Image has been reversed to match A.
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The trauma doctor's pretest probability was shown to predict fracture
successfully (chi-square test, p < 0.05). The average length of a
CT examination was 7 min. Seven patients preferred scintigraphy, 24 preferred
CT, 12 had no preference, and eight did not respond.
Discussion
In 45% (23/51) of patients presenting with continuing pain 10–14 days
after injury but with normal radiography findings, a fracture was diagnosed on
skeletal scintigraphy, but in only 20% (10/51) was the scaphoid involved.
Fractures were detected on CT in only 27% (14/51) of the patients.
Table 1 shows that most of the
discordant interpretations concerned the scaphoid (Fig.
2A,
2B). Although the spatial
resolution of scintigraphy was approximately 10 mm
[19], whereas the CT
z-axis resolution of the 16-MDCT was 0.75 mm
[20], there was no discordance
in the location of concordant fractures.
In all cases of suspected scaphoid fracture at our institution, the
patient's wrist is immobilized using a removable splint. This has the
advantage of not obscuring the bones on subsequent imaging. At present, all
patients with increased focal tracer uptake in the scaphoid bone on
scintigraphy (even if discordant with other imaging findings) are treated as
having a fracture, have 6 weeks of wrist immobilization, and then are
reviewed. Other occult wrist fractures are treated more conservatively and
usually are not reviewed further. In four of seven discrepant cases, arthritic
changes were present, making it more difficult to identify or exclude a
fracture line on CT. One could argue that scintigraphy might be particularly
useful in this situation, but arthropathy can cause diagnostic uncertainty
about skeletal scintigraphy results
[21]. Early blood-pool imaging
might have been helpful [22]
but is not routinely performed at our institution. Four of the patients with
discrepancies underwent follow-up wrist radiography at 6 weeks, and no
fracture was seen on any of these radiographs (Fig.
3A,
3B,
3C). The remaining three
patients did not undergo radiography and were symptom-free after wrist
restraint.
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Fig. 3C. —22-year-old woman with persistent wrist pain after fall.
Follow-up radiograph 6 weeks after injury shows no fracture. Distortion to
bony contour, but no associated sclerosis, is observed. Image has been
reversed to match B.
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The lack of a gold standard limits interpretation of our results. The fact
that scintigraphy appeared to detect more fractures than CT is both intuitive
and in keeping with the current literature
[23]. However, the use of CT
has some inherent advantages. Patients appear to prefer it, no needles are
involved, and examination lengths were about 7 min. A disadvantage of CT is
the large number of slices produced (approximately 600 per examination),
requiring 3D analysis on the workstation and more time for interpretation than
do individual nuclear medicine images. In comparison, scintigraphy involves an
IV injection and a 3- to 4-hr wait before imaging. Moreover, although our
results appear to confirm that skeletal scintigraphy detects more fractures
than CT, our results also raise questions about the true nature of some of the
scintigraphy-positive, CT-negative lesions.
In forming a diagnostic algorithm from our findings, one must recognize the
limitations of our study, such as the lack of gold standard and MRI and the
possibility of the inevitable reporting biases. Our data showed that the
referring clinician's pretest probability was reasonably accurate, but this
finding is contrary to findings suggested by other authors
[2] and, as such, is difficult
to incorporate into a diagnostic algorithm. Despite some inherent advantages
of 16-MDCT, our findings make it difficult to recommend CT as an initial
investigation in suspected scaphoid fracture. CT will probably be useful,
however, in cases of equivocal scintigraphic findings or when needed to
visualize the fracture line, such as to assess healing.
In conclusion, we found that despite the potential advantages of 16-MDCT,
it did not appear to identify as many fractures as did conventional bone
scintigraphy. The finding that some patients have positive scintigraphy
results but normal results on CT and 6-weeks follow-up radiography is
interesting and challenges our understanding of patients presumed to have a
fracture on the basis of skeletal scintigraphy. Further research—for
example, with MRI—is warranted.
Acknowledgments
We are indebted to the technical/radiographic and clerical staffs of both
the nuclear medicine department and the radiology department. We appreciate
the cooperation of the trauma team doctors and the ongoing scientific support
of Siemens.
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Abstract
Introduction
