Keywords
dorsal scaphoid translation - scapholunate dissociation - scapholunate interosseous
ligament
Scapholunate interosseous ligament (SLIL) tears are the most common intrinsic wrist
ligament injuries and are thought to be caused by falls or collisions on a hyperextended
and pronated wrist.[1] SLIL tears may lead to increased and asynchronous motion between the scaphoid and
lunate known as scapholunate dissociation (SLD). Untreated, a predictable carpal instability
pattern ensues, culminating in scaphoid rotary subluxation and abnormal lunate extension,
or dorsal intercalated segment instability (DISI).[2] SLD and DISI can initiate a slow and insidious progression to degenerative arthritis
of the wrist, also known as scapholunate advanced collapse (SLAC).[3]
Over time, additional secondary ligamentous restraints attenuate under load,[4] resulting in additional postural and kinematic deformities.[5] Using three-dimensional computed tomographic models, Omori et al[6] demonstrated that the proximal scaphoid pole translated dorsally and radially in
three patients with chronic SLD. Increased compressive and shear stresses from the
abnormal posture and kinematics of the scaphoid cause cartilage wear on its distal
and proximal poles, and progressive SLAC arthritis.[3]
[7]
[8] Thus, reliably identifying dorsal scaphoid translation (DST) before the loss of
its articular cartilage would have clinically important implications for treatment.
Recently, Meister et al[9] demonstrated that magnetic resonance imaging (MRI) scans detected static DST in
13 of 18 (72%) patients with complete SLIL tears. Using as little as 1% dorsal translation,
the authors reported a sensitivity of 72% and a specificity of 100% for SLIL injury.[9] While the authors contended that MRI was more accurate than radiographic analysis
of dorsal translation, they did not report a technique to measure this parameter radiographically,
nor were we able to identify a technique in the literature. Radiographs are universally
utilized and are also obtained postoperatively to assess reduction and healing over
months and years. Were it sufficiently sensitive, a technique to measure DST using
radiographs would enable a convenient and more cost-effective means to identify this
parameter of SLD both pre- and postoperatively.
The purpose of our study was to determine whether DST can be reliably identified and
measured using radiographs in patients with operatively confirmed complete SLIL rupture
and no degenerative changes. We hypothesized that radiographic DST would correlate
with the presence of a complete SL ligament rupture, and describe two reliable techniques
of DST measurement.
Patients and Methods
Following Institutional Review Board approval, a registry of “SLIL injuries” from
three fellowship-trained hand surgeons (MGC, SWW, SKL) was retrospectively reviewed
to identify eligible patients for study inclusion. Patients were included if they
had adequate preoperative radiographic imaging of their injured wrists, and complete
SLIL tears (all portions) confirmed operatively. Minimum radiographic examination
included posteroanterior (PA) and true lateral wrist radiographs with the forearm
in neutral rotation. True lateral radiographs were confirmed using the scaphopisocapitate
alignment, in which the palmar cortex of the pisiform must lie within the central
third of the interval between the palmar cortices of the scaphoid and capitate.[10] Exclusion criteria included patients with partial SLIL tears, radiographic or operative
evidence of SLAC arthritis, or inadequate imaging. The injured cohort was then matched
with the same number of uninjured control patients who did not have SLIL tears, but
had radiographs performed as part of routine clinical practice for undiagnosed wrist
pain. No control patient was included who had abnormal SL gap, SL angle, or RL angle.
Study patients were deidentified to allow blinded radiological measurements by two
independent reviewers (KC, ESV) on two separate occasions at least 4 weeks apart.
Measurements performed on wrist radiographs included the SL gap, SL angle, radioscaphoid
(RS) angle, RL angle, and DST. SL gap was measured on PA wrist radiographs in the
midportion of the scaphoid and lunate.[11]
[12]
[13] All other angles were measured on true lateral wrist radiographs in 0 degrees of
wrist extension by tracing the longitudinal axes of the appropriate carpal bones.[14]
[15] The scaphoid axis was represented by a tangential line connecting the palmar convexities
of the proximal and distal poles. The lunate axis was perpendicular to a line between
the two distal points of the lunate. The capitate axis was determined by connecting
the midpoints of the proximal and distal articular surfaces.
DST was measured in two different ways on radiographs. The first method, which we
have named the concentric circles method, was performed by outlining the contour of
the proximal scaphoid pole and the scaphoid facet of the distal radius using an electronic
circle template on the picture archiving and communication system viewer ([Fig. 1]). DST was determined by measuring the distance between the centers of these two
circles in a direction normal to the long axis of the radius.
Fig. 1 Concentric circles method—Concentric circles are drawn around the proximal scaphoid
pole and the scaphoid fossa of the distal radius in patients with (A, B) normal wrist radiographs and (C, D) complete scapholunate interosseous ligament (SLIL) tears. The latter demonstrates
dorsal scaphoid translation.
The second method, which was named the dorsal tangential line (DTL) method, involved
drawing a line parallel to the longitudinal axis of the radius that passes through
the dorsal articular rim of the scaphoid facet of the distal radius ([Fig. 2]). DST was considered to be present (positive result) if the proximal scaphoid pole
translated dorsal to this line. Additionally, the amount of scaphoid translation dorsal
to the dorsal tangential line (mm) was measured in a direction normal to the tangential
line.
Fig. 2 Dorsal tangential line method—The dorsal tangential line (DTL) is a longitudinal line drawn through the dorsal articular rim, parallel to the longitudinal
axis of the distal radius. The DTL is drawn in (A, B) control patient and (C, D) scapholunate interosseous ligament (SLIL) tear. The proximal scaphoid pole can be
seen abnormally translated dorsal to the DTL in a patient with (D) complete SLIL tear.
Inter- and intra-rater reliabilities were calculated using a two-way mixed model intraclass
correlation coefficient (ICC) for continuous variables. Interpretation of ICC values
was based on Landis and Koch[16] ([Table 1]). Radiological measurements were also compared statistically using independent samples
t-test for continuous outcomes and chi-square test for dichotomous outcomes.
Table 1
Interpretation of intraclass correlation coefficient (ICC) values
|
ICC
|
Interpretation
|
|
<0
|
Less than chance agreement
|
|
0.01–0.20
|
Slight agreement
|
|
0.21–0.40
|
Fair agreement
|
|
0.41–0.60
|
Moderate agreement
|
|
0.61–0.80
|
Substantial agreement
|
|
> 0.80
|
Almost perfect agreement
|
Results
There were 46 complete SLIL tears in our registry. Twenty-six had inadequate imaging,
leaving 20 study patients with complete SLIL tears which were compared with 20 control
patients. The SLIL group had 19 males and 1 female with a mean age of 44 years (standard
deviation [SD], 9). The mean time from date of injury to operation was 7 months (SD,
6). The control group had 14 males and 6 females with a mean age of 41 years (SD,
14). Neither age (p = 0.43) nor gender (p = 0.04) was statistically significantly different between the two groups once the
p values were adjusted for multiple statistical analyses using the Bonferroni correction.
Carpal Alignment
Patients with complete tears of the SLIL demonstrated significantly increased SL gap,
SL angle, RL angle, and RS angle from the control group ([Table 2]). These measurements are consistent with SLD and DISI.
Table 2
Comparison of carpal alignment between patients with SLIL dissociation and controls
|
SLIL
|
Controls
|
p-Value
|
|
SL gap
|
4.1 mm (±1.4)
|
2.0 mm (±0.5)
|
p < 0.001
|
|
SL angle
|
76.7° (±11.2)
|
50.2° (±9.5)
|
p < 0.001
|
|
RL angle
|
14.4° (±10.4)
|
8.9° (±4.0)
|
p = 0.035
|
|
RS angle
|
63.0° (±8.7)
|
50.0° (±11.4)
|
p < 0.001
|
Abbreviations: RL, radiolunate; RS, radioscaphoid; SLIL, scapholunate interosseous
ligament.
Dorsal Scaphoid Translation
Using both the concentric circles and the dorsal tangential line methods on radiographs,
there was significantly increased dorsal translation of the scaphoid in patients with
SLIL tears compared with the control group ([Table 3]). Mean dorsal translation in the SLIL group was 2.9 mm using the concentric circles
method on radiographs, which was statistically increased over the mean translation
of 0.9 mm in the control group (p < 0.001). Similarly, the SLIL group demonstrated a mean scaphoid translation of 2.5 mm
dorsal to the DTL on radiographs compared with 0.6 mm in the control group (p < 0.001). Fifteen out of 20 (75%) patients with complete SLIL tears demonstrated
translation of the proximal scaphoid pole dorsal to the DTL, while only 4 of the 20
in the normal group demonstrated dorsal translation (p < 0.05).
Table 3
Comparison of dorsal scaphoid translation values measured on radiographs
|
SLIL
|
Controls
|
p-Value
|
|
Concentric circles
|
2.9 mm (±1.7)
|
0.9 mm (±1.1)
|
p < 0.001
|
|
DTL distance
|
2.5 mm (±1.9)
|
0.6 mm (±1.2)
|
p < 0.001
|
|
DTL
|
15/20 dorsal
|
4/20 dorsal
|
p < 0.001
|
Abbreviations: DTL, dorsal tangential line; SLIL, scapholunate interosseous ligament.
Reliability
Inter-rater reliability for the concentric circles and dorsal tangential line method
on radiographs was excellent on both occasions with ICC > 0.80 (“almost perfect agreement”)
([Table 4]). Similarly, intra-rater reliability for each reviewer was also excellent with ICC > 0.90
(“almost perfect agreement”) ([Table 4]).
Table 4
Inter- and intrarater reliabilities of the concentric circles and dorsal tangential
line measurement techniques performed on radiographs
|
Inter-rater (reading #1)
|
Inter-rater (reading #2)
|
Intra-rater (reader #1)
|
Intra-rater (reader #2)
|
|
Concentric circles
|
0.93
|
0.81
|
0.95
|
0.95
|
|
DTL distance
|
0.90
|
0.92
|
0.95
|
0.99
|
|
DTL
|
0.80
|
0.85
|
0.95
|
1.00
|
Abbreviation: DTL, dorsal tangential line.
Discussion
SLD is known to progress to carpal malalignment and ultimately, DISI. Watson et al[17] described a clinical test to dynamically subluxate the dissociated scaphoid onto
the dorsal rim of the radius with manual pressure on its tubercle. Ruby et al[18] identified static scaphoid dorsal translation onto the dorsal rim of the radius
in cadaveric wrists by dividing the SLIL, dorsal capsular ligaments, and the lunate
attachment of the long radiolunate ligament (LRL). However, the concept of static
DST in SLD has not been well documented clinically, and we were unable to identify
techniques to measure this parameter radiographically. Radiographs are a critical
imaging modality for the diagnosis and management of patients with wrist injuries.
Our data demonstrate that radiographs can simply and reliably detect DST in patients
with complete SLIL rupture.
Radiographic DST should be considered to complement conventional radiographic indices
of SLIL injury, such as SL gap, scaphoid malrotation, and increased radiolunate angle
(DISI). It should be recognized that scaphoid dorsal translation is not synonymous
with SLD, rotary subluxation of the scaphoid,[19] DISI, or SLAC arthritis; however, it is generally (but not always) associated with
DISI and scaphoid rotary subluxation.[19] Static DST is concerning, as it is diagnostic of edge-loading of the proximal scaphoid
pole,[6]
[9] and is a harbinger of future cartilage loss.[8] It may precede or coexist with SLAC arthritis, depending on chronicity.
SLD is a spectrum of injury and the presence of abnormal radiographic parameters depends
on the severity of SLIL rupture and the status of its secondary stabilizers.[5] A recent biomechanical study demonstrated that complete division of the SLIL alone
was insufficient to produce a DISI deformity; rather it required at least one secondary
ligamentous stabilizer to be disrupted as well (long radiolunate, scaphotrapeziotrapezoid,
or dorsal intercarpal ligaments).[20] In the same study, only two of the five ligament sectioning sequences demonstrated
DST, and not until the SLIL, LRL, STT (scaphotrapeziotrapezoid), and DIC (dorsal intercarpal
ligament) were fully divided. This spectrum of ligamentous injury may explain why
5 out of 20 patients in our series with complete SLIL disruption did not demonstrate
DST, since they might have been in earlier stages of SL instability. Thus, we feel
that DST is a relatively late finding in the progression of SLD, and may be an early
predictor of future SLAC arthritis.
In a prospective study of 14 patients undergoing SLIL reconstruction, the presence
of DST had a high correlation with postoperative pain while SL gap, SL angle, and
RL angle each demonstrated no correlation.[21] It is likely that static DST creates painful eccentric loading and cartilage shear
between the scaphoid's proximal pole and the dorsal scaphoid facet of the radius.
Static DST is the end stage of the dynamic DST that occurs in Watson's “scaphoid shift
test”,[17] and to the dynamic and painful scaphoid subluxation that occurs with wrist flexion
following SLIL injuries[7]
Scaphoid dorsoradial translation was previously identified using three-dimensional
bone models generated from computed tomography scans in[6] six patients with SLD and DISI. The authors found that the scaphoid translation
generated higher contact areas dorsoradially on the scaphoid facet of the radius.
Limitations of our study include its small sample size and retrospective design, which
did not allow us to investigate clinical factors that may contribute to DST. It is
probable that DST is part of the spectrum of SL instability and occurs only when secondary
stabilizing ligaments are disrupted or attenuate with time. The study was not designed
to measure positive and negative predictive value of DST for SLD, as examiners would
be biased by concomitant radiographic findings of SLD (e.g., gap and DISI) in the
affected subjects.
In conclusion, our data support our hypothesis that DST is associated with SLD and
may be reliably detected radiographically using both the concentric circle and dorsal
tangential line methods. The dorsal tangential line is technically easier to perform
and clinically more practical than the concentric circle method, which relies on availability
of digital imaging software. Either method is quickly and readily performed without
advanced imaging. We believe DST is a useful radiographic parameter for SL instability
that has prognostic and treatment implications, and should be recorded with measures
of SL gap, SL angle, and RL angle.
