SCIENTIFIC ARTICLE

Intraoperative Imaging of the Distal Radioulnar Joint

Using a Modified Skyline View

G. Klammer, MD, M. Dietrich, MD, M. Farshad, MD, MPH, L. Iselin, MD, L. Nagy, MD, A. Schweizer, MD

Purpose Non-anatomic reduction of the sigmoid notch in distal radius fractures may lead tolimited motion, instability, or pain with pronation and supination. Standard radiologicalprojections only poorly capture the sigmoid notch contours in the axial plane. The purposeof this study was to find an intraoperatively feasible radiological projection that will facilitatean axial view of the distal radioulnar joint.

Methods We modified a previously described radiographic projection termed the skylineview for evaluating the distal radius axially. We created intra-articular steps at the sigmoidnotch in solid foam forearm models to identify the best of 12 projections using an imageintensifier. Four observers scored each projection based on the clarity of the sigmoid notchcontour and indicated the presence and location of an intra-articular stepoff.

Results The sigmoid notch was best visualized in the modified skyline view with the wrist inextension and 10° to 15° of dorsal forearm angulation relative to the x-ray path. All observerscorrectly recognized the presence and location of intra-articular steps at the sigmoid notchwith this view. The same forearm angulation with the wrist in flexion did not reach equallygood visibility of the sigmoid notch. Arm position (wrist flexion, forearm rotation, orforearm angulation) and intra-articular stepoff (none, palmar, or dorsal) were dependentdeterminates. Elimination of the variable forearm rotation had minimal effect, indicating thatforearm rotation is not important for visualization of the sigmoid notch.

Conclusions The modified skyline view for visualization of the distal radioulnar joint in an axialplane allows good visibility of the sigmoid notch and reliable identification of stepoffs. Furthercadaver and in vivo studies are required to verify the validity of this method. (J Hand Surg 2012;xx:. Copyright © 2012 by the American Society for Surgery of the Hand. All rights reserved.)

Type of study/level of evidence Diagnostic IV.

Key words Distal radioulnar joint, image intensifier, radiography, skyline view.

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APPROXIMATELY 25% OF fractures of the distalradius extend into the sigmoid notch.1 Becausemalunion with an intra-articular step-off at the

distal radioulnar joint (DRUJ) may lead to instability,

From the Department of Orthopaedic Surgery, University of Zurich, Balgrist, Zurich, Switzerland; andthe Orthopaedic and Trauma Service, Royal Adelaide Hospital, Adelaide, Australia.

Received for publication March 4, 2011; accepted in revised form December 9, 2011.

No benefits in any form have been received or will be received related directly or indirectly to thesubject of this article.

Corresponding author: Georg Klammer, MD, Department of Orthopaedic Surgery, Uniklinik Bal-grist, Forchstrasse 340, 8008 Zürich, Switzerland; e-mail: georg.klammer@balgrist.ch.

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limited motion, or pain with pronation and supination,the primary goal in acute trauma management is ana-tomic reduction. To date, standard radiological projec-tions do not allow for satisfactory visualization of theDRUJ contours. Fractures and intra-articular step-offs,particularly in the axial plane, may only be detectedusing computed tomography (CT) scans.2 However,ntraoperative CT scans are not readily available inost situations.A true axial view can be obtained with the x-ray

eam oriented parallel to the DRUJ axis. However, inhis projection the superposition of bony and soft tissuetructures of the elbow and forearm obstruct visualiza-

ion of the sigmoid notch. A near-axial view of the

© ASSH � Published by Elsevier, Inc. All rights reserved. � 1

2 DRUJ IMAGING WITH THE SKYLINE VIEW

DRUJ may be obtained with the forearm slightly angu-lated relative to the x-ray beam and with maximal wristflexion or extension. Jacob and Clay3 proposed a pro-jection, termed the skyline view, for evaluating dorsalscrew penetration in plate fixation of distal radius frac-tures. This projection is achieved by placing the wrist inflexion, the forearm in full supination, and the elbowflexed 75° to 80°.

The aim of this study was to find an intraoperativelyfeasible radiological projection to provide an axial viewof the DRUJ, with the goal of improving reduction ofacute fractures and corrective osteotomies. We hypoth-esized that a modified skyline view will facilitate intra-operative axial visualization of the DRUJ with goodvisibility of the sigmoid notch, allowing for reliableidentification of stepoffs.

MATERIALS AND METHODSWe used a Synbone (Synbone AG, Malans, Switzer-land) solid foam model of the hand, wrist, and forearm.We covered all bony surfaces with a zinc spray (ca-thodic corrosion protection; Motipo Dupli GMBH,Hassmersheim, Germany) to obtain sufficient radio-opacity. We placed the model into combinations of thefollowing wrist and forearm positions to modify theoriginally described skyline view3 and acquired fluoro-scopic images: (1) with the wrist in maximal extensionor maximal flexion; (2) with the forearm in full supi-nation, neutral position, or full pronation; and (3) withvolar or dorsal angulation of the longitudinal forearmaxis (10° to 15°) relative to the x-ray path as describedby Jacob and Clay.3

This resulted in 12 different possible positioningsetups of the models. We angled the forearm slightlyradially or ulnarly to match the anatomic inclination ofthe sigmoid notch in the coronal plane.4 This may beestimated from standard anteroposterior films. We col-lected 3 series of image intensifier images for a modelwithout intra-articular step-off at the sigmoid notch andfor 2 separate specimens with a 1-mm stepoff in theaxial plane at either the dorsal or volar third of the jointsurface to simulate malunion. We achieved intra-articular -offs by osteotomy in the coronal plane. Wedisplaced fragments ulnarly and glued them together(Fig. 1).

We presented the images of all 3 series (36 images)to 2 senior orthopedic residents and 2 hand surgeons(144 ratings). They were asked to assign a score ofclarity from 0 to 100 points to each view according tosubjective quality of visualization of the sigmoid notchjoint surface. In addition, they were asked to indicate

presence and position of a stepoff.

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We performed a 5-factorial analysis of variance withinteractions up to order 3 to assess the effect of thefactors arm positioning (wrist flexion, forearm rotation,or forearm angulation), intra-articular stepoff (none,palmar, or dorsal), and observer. We quantified poten-tial interdependencies between factors by stepwiseelimination of interactions and variables using R2 val-ues. We compared scores between projections usingpost hoc tests with Bonferroni correction. We assessedinterobserver reliability (intraclass correlation) sepa-rately for the 4 combinations of wrist flexion and fore-arm angulation using a 2-way random model with fac-tors observer and image (9 images for each analysis).

RESULTSFigure 2 shows all observers’ mean scores per projec-tion (ranges) and percentages of correctly recognizedstepoffs.

Arm position (wrist flexion, forearm rotation, orforearm angulation) and intra-articular stepoff (none,palmar, or dorsal) were dependent (R2 of 89%) deter-minates. Elimination of the variable forearm rotationslightly reduced the R2 to 88%, indicating that forearmrotation is not an important parameter for visualizingthe sigmoid notch. Hence, forearm rotation was notconsidered for the subsequent analysis. All other vari-ables were interdependent.

Highest clarity scores for visualizing the sigmoidnotch were achieved for the projection with wrist ex-tension and forearm dorsal angulation consistently forall 3 series (Fig. 3). However, the projection with wristflexion and forearm dorsal angulation also scored highin the series with an intra-articular step at the palmar

FIGURE 1: Illustration of the model. In this example, thecoronal osteotomy was placed at the dorsal third of thesigmoid notch, and the fragment was displaced 1 mm ulnarly.For better visibility of the intra-articular step, the ulna and thebones of the hand are not shown.

third (Fig. 3). For the projection with wrist extension

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DRUJ IMAGING WITH THE SKYLINE VIEW 3

and forearm dorsal angulation, the observers correctlyidentified and located all intra-articular steps. However,correct classification was not achieved with the other

FIGURE 2: Views of the 12 possible projections of forearm/wthe sigmoid notch. For each projection, mean scores (ranges)recognized stepoffs are indicated. Values represent all 3 series.

projections (range, 8% to 67%) (Fig. 2).

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Interobserver reliabilities for the clarity scores of theDRUJ were 0.52 for the projection that achieved bestvisualization of the sigmoid notch (wrist in extension

lacement of the model with a palmar intra-articular stepoff atned by the observers are shown and percentages of correctly

rist passig

and forearm in dorsal angulation) and 0.73 for the view

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orsal

4 DRUJ IMAGING WITH THE SKYLINE VIEW

in the same angulation but with the wrist in flexion.However, the latter projection had inferior visibility ofthe sigmoid notch (lower scores attributed by the ob-servers and lower percentages of correctly recognizedand localized intra-articular steps) (Fig. 2). Projectionswith the forearm in volar angulation had low interob-server reliabilities, with 0.22 and 0.24 in wrist extension

FIGURE 3: Estimated marginal means for scores reached by thThe projection with the wrist in extension and the forearm in d

FIGURE 4: Positioning of the patient’s arm to attain bestvisualization of the DRUJ surface. The wrist is placed inextension and the forearm is angulated dorsally 10° to 15°relative to the x-ray path.

and flexion, respectively.

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DISCUSSION

Degenerative changes of the DRUJ, ulnar variance, andtransverse fractures (axial plane) including steps can beassessed using standard posteroanterior radiographs.5,6

However, these radiological projections do not suffi-ciently visualize the DRUJ contours to verify anatom-ical reduction in acute trauma. Hence, fractures andintra-articular step-offs in the frontal or coronal plane atthe sigmoid notch may be unapparent or underesti-mated when evaluated using standard radiographs, andCT examination may be warranted.2

Radiological projections must be perpendicular tothe anatomical region of interest to precisely visualizethe contours of bony surfaces or relative implant posi-tioning. In standard views, most joint surfaces of thedistal radius are projected obliquely. Because intraop-erative CT scans or 3-dimensional image intensifiersare not commonly available, various simple radiologi-cal views have been described to improve visualizationof different regions of surgical interest that consider thenatural anatomical tilt of the distal radius. Most viewsaddress dorsal screw penetration in volar locking plat-ing or subchondral screw positioning at the distal ra-dius.7–16 Lundy et al9 performed a cadaveric studyevaluating tilted radiographs for the assessment of frac-tures of the lunate facet. However, their view was

ossible combinations of wrist position and forearm angulation.angulation scored best in all 3 series.

e 4 p

designed to highlight intra-articular step-offs of the lu-

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osteo

DRUJ IMAGING WITH THE SKYLINE VIEW 5

nate facet in the sagittal plane and is not able to excludeincongruencies of the sigmoid notch in the frontalplane.9

This study describes the use of a modified skylineview with an intraoperatively available image intensi-fier, as previously proposed by Jacob and Clay3 for theevaluation of dorsal screw penetration in plate fixationof distal radius fractures. The modification, namelywrist extension (Fig. 4), facilitated good visualization ofthe sigmoid notch and identification of all stepoffs in-dependent of forearm rotation.

To illustrate the value of the modified skyline viewin clinical practice, the case of a 28-year-old patient isbriefly summarized. The patient presented late after adistal radius intra-articular fracture with persistent pain-ful impaired wrist flexion and supination. Conventionalx-ray and CT scan revealed a Frykman type IV frac-ture1 with malunion of the ulnar palmar fragment and3-mm proximal settling without radioulnar displace-ment. Arthroscopy confirmed sufficient cartilage qual-ity of the radiocarpal joint, and, as far as visible, of thesigmoid notch. We performed an intra-articular distalradius osteotomy through the lunate facet and sigmoidnotch. After the osteotomy, reduction and fixation ofthe fragment and anatomic restoration of the sigmoidnotch contour were asserted intraoperatively using themodified skyline view and confirmed with an axial CTscan before patient discharge (Fig. 5).

Although the modified skyline view allowed forgood visualization of the sigmoid notch and did not failto identify any stepoff, the limitations of this studyshould be carefully considered. For instance, the resultsmay not be translated directly for use in patients be-

FIGURE 5: Case example. A Intraoperative image intensifiePostoperative axial CT scans confirmed correct location of the

cause of the ex vivo design of the study. Evaluation of

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the best projection using solid foam models may beaffected by the lack of soft tissues and poor articularconstraint. In addition, zinc coating does not reflectactual variations in cortical thickness or metaphysealdensities within the bones of the wrist.

The best-performing view for visualization of thesigmoid notch was with the wrist in extension and 10°to 15° of dorsal forearm angulation relative to the x-raypath. This view allowed all observers to correctly iden-tify all stepoffs. The interobserver reliability of theclarity score was lower compared with that with thehand in flexion. However, this only means that observ-ers agree better that the view with the wrist in flexion isworse than the view with the wrist in extension. Fur-thermore, the score assigned by the observers reflectstheir subjective impression of how well the sigmoidnotch outlined in each view. Hence, these scores aresemiquantitative scores and do not provide informationabout whether an intra-articular step was correctly rec-ognized. We did not calculate intraobserver reliabilitiesbecause the aim of this study was to find the best viewfor visualization of the sigmoid notch and not to vali-date a scoring system for visibility of the sigmoid notch.Finally, we achieved the main outcome of this study—namely, identifying step-offs—100% using the modi-fied skyline view, corresponding to a perfect interob-server reliability.

Further studies, such as cadaver studies and in vivoinvestigations, are needed to validate the findings of thisstudy.

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