Abstract
Background: The accuracy of diagnostic imaging modalities that are
currently used to evaluate dynamic scapholunate ligamentous instability is
equivocal. Ultrasound is commonly used for a wide variety of diagnostic
purposes in orthopaedics. The purpose of the present study was to determine
the efficacy of ultrasound in the diagnosis of dynamic scapholunate
ligamentous instability.
Methods: Two groups of individuals were prospectively studied. Group
A included patients with a clinical diagnosis of unilateral dynamic
scapholunate ligamentous instability, and Group B included asymptomatic
volunteer control subjects. Dynamic ultrasound examinations of the dorsal
portion of the scapholunate ligament in both wrists of all individuals were
performed by radiologists. The radiologists were blinded with regard to the
group to which each person belonged as well as with regard to the affected
wrist in the patients in Group A. Arthroscopic examinations of the affected
wrist in all of the patients in Group A were then performed by surgeons who
were blinded with regard to the results of the ultrasound examination, and the
results of the arthroscopic and ultrasound examinations were compared. The
ability of ultrasound to discern asymptomatic from symptomatic individuals was
also determined.
Results: Over a period of 1.5 years, a total of sixty-four wrists
were evaluated in fourteen patients (Group A) and eighteen normal subjects
(Group B). All fourteen nonaffected wrists in Group A and all thirty-six
wrists in Group B were correctly identified as normal with use of ultrasound.
Of the fourteen affected wrists in Group A, thirteen were found to have
scapholunate ligament laxity on the basis of arthroscopy (twelve wrists) or
arthrotomy (one wrist); six of these thirteen wrists had been correctly
identified as abnormal with use of ultrasound (a true-positive result), and
seven had false-negative results. There was one true-negative result. The
ability of ultrasound to differentiate between normal and abnormal wrists was
significant (p < 0.001). For the sixty-four wrists, statistical analysis
revealed that ultrasound had a sensitivity of 46.2%, a specificity of 100%,
and an accuracy of 89.1%.
Conclusions: We conclude that ultrasound has a high specificity and
accuracy but a low sensitivity for the evaluation of dynamic scapholunate
ligamentous instability, and we recommend its use as an adjunct to other
diagnostic modalities for this purpose.
Level of Evidence: Diagnostic study, Level IV-1
(case-control study). See Instructions to Authors for a complete description
of levels of evidence.
Taleisnik first described the concept of dynamic scapholunate ligamentous
instability in
19801. This
condition is characterized by normal findings on plain radiographs and
positive provocative physical examination maneuvers that elicit and reproduce
the symptoms of pain and instability. Anatomically, three distinct regions
comprise the scapholunate interosseous ligament: dorsal, proximal, and
palmar2. Ruby et al.
found that disruption of the dorsal portion of the scapholunate interosseous
ligament caused substantial alteration in the normal relationship between the
scaphoid and the
lunate3. Berger et
al. noted that it is difficult to define the length or cross-sectional
architecture of the scapholunate interosseous ligament with accuracy and
reproducibility4.
A multitude of diagnostic modalities have been used to assist the surgeon
in the diagnosis and treatment of dynamic scapholunate ligamentous
instability, including dynamic plain radiography, arthrography, bone-scanning,
magnetic resonance imaging, and magnetic resonance
arthrography5.
However, each of these modalities has disadvantages, including radiation
exposure and high cost. Arthroscopy is considered to be essential for the
evaluation of ligamentous instability in the
wrist6, and
arthrotomy is considered to be the "gold" standard for this
purpose7.
Ultrasound is a noninvasive and cost-effective modality that has been used
widely throughout orthopaedics for the evaluation of soft-tissue masses and
the detection of foreign bodies, tendon ruptures, rotator cuff injuries,
tendinitis, and ganglion cysts. It also has been used to evaluate ulnar
collateral ligament injuries of the
thumb8 and injuries
of the interosseous membrane of the
forearm9. Its
applicability in the evaluation of dynamic wrist instability has not been
determined. The purpose of the present study was to determine the efficacy of
ultrasound in the evaluation of dynamic scapholunate ligamentous instability
with use of a prospective protocol.
Two groups were evaluated in this study. Group A included patients with a
clinical diagnosis of unilateral dynamic scapholunate ligamentous instability
of either traumatic or nontraumatic etiology. This diagnosis was made if the
patient had pain with palpation at the dorsal scapholunate interval and/or
pain on the Watson scaphoid shift test (pain with or without a clunk when
pressure is applied to the scaphoid tuberosity with use of the examiner's
thumb while the patient's wrist is passively moved from ulnar deviation to
radial deviation in the coronal
plane10) as well as
normal findings on radiographs of the wrist. All of the patients in Group A
had had a failure of nonoperative treatment (that is, they continued to
experience pain and discomfort in the wrist with activities of daily living
and/or with more rigorous use of the hand despite nonoperative treatment) and
had been scheduled for wrist arthroscopy as part of a plan for the evaluation
and treatment of wrist instability. Patients with static wrist instability,
bilateral wrist instability, or previous wrist surgery were excluded.
Group B included volunteer subjects with asymptomatic wrists and normal
clinical findings: no radiographic, magnetic resonance imaging, or
arthroscopic examinations of the wrist were performed for these subjects. All
subjects provided informed consent, and the study was approved by the
Investigative Review Board and the Committee for Protection of Human
Subjects.
Ultrasound examinations of the dorsal portion of the scapholunate
interosseous ligament in both wrists of all patients and subjects were
performed by a board-certified radiologist (M.L.P.) who is a subspecialist in
musculoskeletal and ultrasound radiology. The radiologists were blinded with
regard to the group to which each patient or subject belonged as well as with
regard to the affected wrist (left or right) in the patients in Group A. To
this end, the individuals in Group A were instructed not to disclose their
designation as patients to the radiologists. Furthermore, they were instructed
to remove any wrist braces or splints that might reveal their group identity.
The individuals in Group B were similarly advised to not divulge their group
identity to the radiologists.
Each examination was performed in a standardized fashion. With the patient
seated, the shoulders were adducted, the elbows were flexed to 90°, and
both forearms were pronated on a firm surface
(Fig. 1). The ultrasound wand
was placed on the dorsal aspect of the slightly flexed wrist, just distal to
Lister's tubercle. A linear 5 to 10-MHz probe (Entos CL15-7; Philips Medical
Systems, Andover, Massachusetts) was used to examine the wrist. First the
scaphoid and lunate bones were visualized with the probe, and then the
intervening dorsal portion of the scapholunate interosseous ligament was
identified (Fig. 2). The
examination was performed with the wrist in neutral ulnar-radial deviation
initially. Dynamic ultrasound examinations were then performed by first
visualizing the scapholunate ligament with the probe applied dorsally on the
wrist while the fist was clenched. Then, with the probe still applied to the
dorsum of the wrist (and with the ligament visualized dynamically with use of
the ultrasound signal), the wrist was actively moved first in the radial
direction and then in the ulnar direction. Any widening of the interval
between the scaphoid and the lunate bones and/or abnormality of the ligament
as depicted by the ultrasound signal was noted.
The criteria for an abnormal ligament on the ultrasound examination were
the lack of a smooth, homogeneous, echogenic appearance of the dorsal
scapholunate interosseous ligament (Fig.
3); a wavy or undulating appearance of the ligament
(Fig. 4); or diastasis of the
scapholunate interval. Only one of these three pathologic findings needed to
be present during the static or dynamic maneuvers for the ligament to be
considered abnormal. All findings resulting from the ultrasound examination
were recorded by the radiologist. The patients and the asymptomatic subjects
were instructed not to disclose the results of the ultrasound examination to
the surgeons.
All patients in Group A subsequently underwent an arthroscopic examination
of the radiocarpal and midcarpal joints of the wrist, with the surgeon unaware
of the results of the ultrasound examination. The Geissler classification
system was used to grade ligamentous
laxity11. For the
purposes of the present study, Geissler grade-1 and 2 laxity (no gap or
incongruency or a gap of less than the width of a probe [2 mm] in the presence
of incongruency) were considered to be normal and grade-3 and 4 laxity
(incongruency with a gap that was wide enough to allow the passage of a probe
or a 2.7-mm arthroscope) were considered to be abnormal for correlation with
the ultrasound findings. The decision to proceed with definitive surgical
treatment of the wrist was based on the intraoperative findings. These
surgical procedures were performed at the same time as the arthroscopic
examination of the wrist and included anterior and posterior interosseous
neurectomy, dynamic scapholunate interosseous ligament repair, or
scaphoidectomy and four-corner arthrodesis.
It was assumed that normal, asymptomatic wrists would have normal
arthroscopic findings. Therefore, the subjects in Group B did not undergo
arthroscopic examination of the wrist.
Statistical Analysis
On the basis of a pilot study, a power analysis was performed. For a beta
of 0.90 and an alpha of 0.05, it was estimated that a sample size of at least
fourteen individuals per group would be required. The differences in the
ability of ultrasound to correctly identify an abnormal as opposed to a normal
ligament were calculated with use of the Fisher exact test, with the level of
significance set at p < 0.05. Demographic differences between the groups
were evaluated with use of a two-sample t test (with unequal variance) with
regard to age and with use of the Fisher exact test with regard to gender and
handedness.
Each wrist in all patients and subjects was considered individually for the
calculation of the sensitivity (true positive/[true positive + false
negative]), specificity (true negative/[true negative + false positive]), and
accuracy ([true positive + true negative]/[true positive + true negative +
false positive + false negative]) of ultrasound for the entire series.
Between February 1999 and June 2000, fourteen patients (Group A) and
eighteen normal control subjects (Group B) were evaluated. Group A included
nine men and five women with a mean age of 28.4 years (range, nineteen to
forty years); eleven patients were right-hand dominant. Group B included
thirteen men and five women with a mean age of 29.5 years (range, twenty-two
to thirty-seven years); fourteen subjects were right-hand dominant. There were
no significant differences between the groups with respect to age, gender, or
handedness.
In Group B, both wrists of all eighteen subjects were correctly identified
as normal with use of ultrasound, for a total of thirty-six true-negative
results. There were no false-positive results. In Group A, all fourteen
unaffected wrists were correctly identified as normal as well, for a total of
fourteen true-negative results.
Of the fourteen affected wrists in Group A, thirteen were found to have
Geissler grade-3 or 4 scapholunate ligament laxity on the basis of arthroscopy
(twelve wrists) or arthrotomy (one wrist)
(Fig. 4); six of these thirteen
wrists had been correctly identified as abnormal with use of ultrasound (a
true-positive result), and seven had been incorrectly identified as normal
with use of either static or dynamic ultrasound (a false-negative result).
There was one true-negative result in this group
(Table I).
For the entire series, ultrasound had a sensitivity of 46.2%, a specificity
of 100%, and an accuracy of 89.1%. The ability of ultrasound to detect dynamic
scapholunate ligamentous instability as opposed to a normal scapholunate
interosseous ligament was significant (p < 0.001).
Wrist arthrography has historically been the radiographic test of choice
for the evaluation of the status of the interosseous ligaments and the
triangular fibrocartilage complex. However, arthrography only reveals the
presence or absence of communication of contrast medium between or within the
wrist compartments and there is no implication that such communication is
correlated with symptoms. Previous studies have documented false-positive
results (i.e., the communication of contrast medium) in the asymptomatic wrist
of patients with contralateral
symptoms12.
Arthrography has low sensitivity and specificity when compared with
subsequent wrist arthroscopy or arthrotomy. Weiss et al. compared
triple-injection arthrography with arthroscopy in a study of fifty patients
with the clinical diagnosis of internal derangement of the
wrist13. When
compared with arthroscopy, triple-injection arthrography had a sensitivity,
specificity, and accuracy of 56%, 83%, and 60%, respectively, for the
detection of ligamentous tears.
Similarly, cineradiographic examination of the wrist can aid in the
detection of the moment and general location at which a patient's instability
occurs, and the findings can be correlated with symptoms. However, this
modality also has a low sensitivity when applied to wrist
pathology14. The
addition of arthrography prior to the cineradiographic examination (i.e., a
cinearthrographic study of the wrist) has been documented to have a
sensitivity, specificity, and accuracy of 60%, 100%, and 84%, respectively,
for the evaluation of scapholunate ligament
injuries13.
Although these values compare favorably with the results of ultrasound as
described in the present study, the added cost and radiation exposure may be
considerable.
Magnetic resonance imaging offers some advantages in that it is
noninvasive, it does not involve ionizing radiation, and it provides the
ability to visualize other anatomic structures or lesions in the wrist.
Unfortunately, it is also costly and its efficacy in identifying ligamentous
abnormalities of the wrist is
questionable5.
Schweitzer et al. reported that it had a sensitivity, specificity, and
accuracy of 25%, 86%, and 64.3%, respectively, for the evaluation of the
scapholunate
ligament5. Magnetic
resonance arthrography increases sensitivity, but it also increases cost,
testing time, and patient discomfort.
Currently, the optimal modality with which to reliably diagnose
interosseous ligamentous injuries of the wrist is still elusive. In the
present study, we sought to evaluate the efficacy of ultrasound as a
diagnostic modality for the detection of dorsal scapholunate interosseous
ligamentous laxity and found that it had a sensitivity, specificity, and
accuracy of 46.2%, 100%, and 89.1%, respectively. The specificity and accuracy
that we observed were higher than those that have been documented in
association with other techniques, as discussed above. The low sensitivity in
our study is a matter of concern and tempers the designation of ultrasound as
a potentially optimal diagnostic modality. However, when used in conjunction
with an accurate physical examination for the appropriate patient population,
ultrasound can provide important information to assist the surgeon in this
diagnostic dilemma.
Several technical considerations regarding the ultrasound examination
warrant discussion. First, the technique is operator-dependent. The
radiologists performing these examinations were experienced in the use of
ultrasound techniques for other orthopaedic applications. Second, it is
theoretically possible that a partially healed ligament may be associated with
a negative result (no tear) during an ultrasonographic examination but will
not be strong enough to withstand the stress placed on it during an
arthroscopic examination. In such a scenario, the ultrasound examination would
yield a false-negative result. This is a limitation of any noninvasive and
some invasive diagnostic modalities.
Third, we surmise that a false-negative result may occur if the dorsal
aspects of the radiocarpal and intercarpal ligaments are mistakenly identified
as the dorsal portion of an intact scapholunate interosseous ligament that may
indeed be torn. Also, if the dorsal aspects of the radiocarpal and intercarpal
ligaments are scarred to the dorsal aspect of a torn scapholunate interosseous
ligament, as is sometimes encountered in cases of chronic instability, a
false-negative result may be obtained. Fourth, the quantitative measurements
of the scapholunate gap during dynamic maneuvers may be difficult to reproduce
because of the difficulty of localizing the exact same location on the dorsal
aspects of the lunate and scaphoid for measurement between different
ultrasound frames. Furthermore, care must be taken to avoid displacing the
ultrasound probe off of the wrist during these dynamic maneuvers.
On the basis of our findings, we believe that the use of ultrasound in the
workup of a patient with chronic wrist pain is most appropriate when the
physical findings are suggestive of dynamic scapholunate ligamentous
instability but the surgeon cannot rule out other causes of the pain with
certainty. A positive result on an ultrasound examination will substantiate
the scapholunate ligament injury as a major, if not the sole, cause of the
symptoms because the rate of false-positive results is extremely low. This
piece of information is highly valuable in the preoperative discussion when
contemplating surgical treatment.
The results of the present study suggest that, if the results of an
ultrasound examination are negative, the possibility of a torn scapholunate
ligament as well as other causes of wrist pain will still need to be
considered. If a patient is still symptomatic despite nonoperative care, then
we recommend a diagnostic arthroscopic examination of the wrist for the
evaluation of the integrity of the scapholunate ligament as well as other
intra-articular structures.
We conclude that ultrasound has a high specificity but a low sensitivity
for the diagnosis of dynamic scapholunate instability. We recommend that it be
used as an adjunct to other diagnostic measures for this purpose.
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