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Kinematics of the scaphoid shift test
Kinematics of the Scaphoid Shift Test Scott W. Wolfe, MD, New Haven, CT, Anuj Gupta, MD, Boston, MA, Joseph J. Crisco, II!, PhD, Providence, RI Twenty-five uninjured subjects (50 wrists) were examined clinically and fluoroscopically during performance of the scaphoid shift test. Wrists were placed into 3 groups on the basis of the degree of palpable carpal motion that occurred during the clinical examination. Kinematic parameters of rotation and displacement were calculated from digitized images of the carpals at rest and at maximum displacement. On clinical exam, 36% of normal individuals had positive findings on scaphoid shift test. Dorsal displacement of the scaphoid was not significantly associated with positive scaphoid shift test results in these subjects, while total displacement of the scaphoid (the sum of axial and dorsal displacement) was significantly associated with positive test results. The principle confounding factor appeared to be a high degree of displacement that occurred at the capitolunate joint in some individuals, termed a "midcarpal shift." The data demonstrate that despite a high prevalence of positive scaphoid shifts among uninjured individuals, the ability to accurately detect dorsal displacement of the scaphoid using the scaphoid shift test is limited. On the basis of their findings, the authors recommend that positive test results be confirmed fluoroscopically. (J Hand Surg 1997;22A:801-806.)
As the principle link between the proximal and distal carpal rows, the scaphoid plays a critical role in coordinating and stabilizing movements of the wrist. Incomplete tears of the intrinsic or extrinsic ligaments that support the scaphoid may impair its ability to function effectively and may result in persistent pain and dysfunction with loading or activities.l-3 Such "dynamic" instability of the wrist may elude demonstration by static radiographs and may be visualized only on stress radiographs or motion studies. The scaphoid shift test has been described as a useful clinical tool in the diagnosis of dynamic
From the Yale Hand and Upper ExtremityCenter, Department of Orthopaedics and Rehabilitation,Yale UniversitySchool of Medicine, New Haven, CT, and Orthopaedic Research, Department of Orthopaedics, RhodeIsland Hospital,Providence,RI. Supportedin part by National Institutes of HealthgrantAR44005. Received for publication Feb. 13, 1996; accepted in revised form March 19, 1997. No benefitsin any form have been receivedor will be receivedfrom a commercialparty related directlyor indirectlyto the subject of this article. Reprint requests: Scott W. Wolfe, MD, Yale University School of Medicine, Department of Orthopaedics and Rehabilitation, RO. Box 208071, New Haven,CT 06520-8071.
wrist instability, particularly when it reproduces the patient's symptoms. ~,4,5 In this examination, deliberate load is applied to the scaphoid tubercle as the wrist is brought from ulnar to radial deviation, and the examiner palpates for dorsal displacement of the proximal pole of the scaphoid from the scaphoid fossa of the distal radius (Fig. 1). There is a spectrum of mobility that may occur during the maneuver, and the test results may be positive in up to one third of uninjured individuals. 6,7 The actual motion that occurs among the carpals during performance of the test has not been characterized. The purposes of this study were to determine the displacement and rotation of the scaphoid, lunate, and capitate during the "scaphoid shift test in uninjured subjects and to compare the results of the clinical examination to findings on fluoroscopic analysis.
Materials and Methods A total of 25 subjects (50 wrists) without history of prior wrist injury or dysfunction were examined in this study. Informed consent for the study was obtained per a Human Investigations Committee protocol. The modification of the scaphoid shift test as The Journal of Hand Surgery
801
[102 Wolfe et al. / Kinematics of Scaphoid Shift
A
B
Figure 1. Fluoroscopic lateral views of a scaphoid shift test performed on a patient with surgically confirmed scapholunate dissociation. (A) The wrist at rest (no load applied). (B) Maximally loaded image during the scaphoid shift test. Note the subluxation of the scaphoid onto the dorsal lip of the distal radius that occurred during application of load.
described by Lane was performed on each wrist by a single examiner. 2,4 The maneuver was repeated five times to precondition the wrist ligamentsS; grading, on a scale of 0-2, was based on the results of the fifth cycle. Zero represented no appreciable subluxation of the scaphoid. A grade of 2 represented a perceived subluxation of the scaphoid from the scaphoid fossa, with a palpable "clunk" that occurred upon release of thumb pressure. A grade of 1 was assigned to those wrists in which some carpal bone movement could be appreciated but no frank clunk or subluxation occurred. The exam was then repeated on the opposite wrist. The scaphoid shift test was repeated under fluoroscopy. A fluoroscopy unit (XiScan, XiTec, Inc., South Windsor, CT) and a video cassette recorder were peripherally attached to a personal computer; which was used as the means of collecting data. A video digitizing card (Video Spigot Pro NuBus, SuperMac Technologies, Sunnyvale, CA) was installed in the computer, allowing the user to collect and store digital images from the fluoroscope at a rate of approximately 12 frames per second. The subject was seated exactly as before, face-to-face with the examiner. The C-ann of the fluoroscope was adjusted to give a lateral view of the wrist without interfering with the examination. Several cycles of the scaphoid shift test were recorded for both the left and fight wrists for each subject.
Kinematic Analysis
The fluoroscopic tapes were reviewed and images were selected to represent the resting state (ie, the examiner was not applying pressure with his thumb) and the loaded state (the image with the maximum displacement of the carpus). For both the resting and loaded images, bony contours of the carpal bones (scaphoid, lunate, and capitate) and distal radius were digitized using MedVision software (Evergreen Technologies, Hartford, CT). The kinematic parameters of the carpal bones were calculated using a previously described contour registration technique. 9 Briefly, the two-dimensional contour of the bone can be considered a unique descriptor that is invariant to rigid body motion. This method registers or matches 2 digitized contours of the same bone at 2 different positions by quantitively matching their curvatures. The process yields a dense set of displacement vectors from which kinematic parameters (rotation and displacement) are determined. The advantage of this method is that the kinematic parameters can be accurately determined without identifying specific landmarks or surgically introducing radiopaque markers. Displacements of the scaphoid and lunate were described in reference to a radial coordinate system defined at the point of maximal curvature (point A) on the dorsal lip of the distal radius (Fig. 2). Displacements of the capitate were described in a coor-
The Journal of Hand Surgery / Vol. 22A No. 5 September 1997
Dotstl
Rotations were defined as positive if the carpal bone extended in response to the applied load and as negative if the carpal bone flexed.
Statistical Comparisons
~- Axial
7 VolarR a ~
I
D' ~T D
803
Rotation=0~
Unloaded
Displacement and rotation were compared to the results of the clinical scaphoid shift test (groups 0, 1, and 2) using a factorial (nonrepeated) analysis of variance with a post-hoc Fisher pairwise least significant difference (PLSD) test (Statview SE, Abacus Concepts, Berkeley, CA). Comparisons of kinematic parameters among different groups were performed using an unpaired, two-tailed Student's t-test. Additionally, a linear regression analysis was performed to determine the relationship between rotation of the carpal bones and their dorsal displacement.
AA
Figure 2. Calculation of scaphoid displacement in terms of radial units (RU), defined as the distance between points A and B. Point D on the scaphoid contour was defined as the point closest to the midpoint of the radial articular surface. Total displacement was the length of the displacement vector (D-D'). AT is the dorsal displacement vector; AA is the axial displacement vector. Rotation in flexion was defined as a positive rotation.
dinate system similarly defined on the dorsal lip of the lunate. Displacements were computed in terms of radial units (RU). A radial unit (RU) was defined as the distance between the vertices of the dorsal and volar lips of the distal radius. Use of RUs allowed comparison of displacement data between wrists of different sizes. To calculate displacement between resting and loaded images of the scaphoid shift test, a point (D) on the contour of the scaphoid and lunate that was closest to the midpoint between the dorsal and volar lips of the radius on the resting image was defined (Fig. 2). Using the contour registration technique, the computer was able to define the same point on the loaded image (D'). Total displacement of the bone was defined as the length of the displacement vector (D-D'). Dorsal displacement (AT) was defined as the length of the displacement vector perpendicular to the longitudinal axis of the radius. Axial displacement (AA) was defined as the length of the displacement vector parallel to the longitudinal axis of the radius.
Results Fifteen wrists (30%) had grade 0 clinical scaphoid shift, 17 wrists (34%) had a grade 1 shift, and 18 wrists (36%) had a grade 2 shift. During the fluoroscopic imaging of the scaphoid shift test, 13 of 50 wrists (26%) demonstrated dorsal subluxation of the scaphoid proximal pole over the dorsal lip of the distal radius. Of these 13 wrists, only 6 were in group 2. An unexpected finding, however, was capitate dorsal subluxation from the capitolunate (CL) joint in 13 of the remaining 37 wrists. This type of motion was referred to as a "midcarpal shift" and was not associated with appreciable dorsal displacement of the scaphoid (Fig. 3). Simultaneous axial widening of the radiolunate and radioscaphoid joints was noted during the midcarpal shift.
Calculated Carpal Displacements Displacements for the scaphoid, lunate, and capitate in the 50 wrists are displayed in Figure 4. As expected, the scaphoid exhibited substantial dorsal and total displacement; an unexpected finding was the nearly equivalent amot~nt of capitate displacement. When analyzed by group, there was no significant difference between groups 0, 1, and 2 in scaphoid dorsal displacement or rotation. Similarly, there was no significant difference of rotation or displacement of the capitate and lunate between groups 0, 1, and 2. There was a statistically significant difference in scaphoid dorsal displacement between group 0 and the other 2 groups combined (p < .03) (Fig. 5).
804
Wolfe et al. / Kinematics of Scaphoid Shift
0
1
2
8hilt @ ~ p
Figure 5. Dorsal displacement of the carpals. Dorsal displacement of the scaphoid is significantly decreased in group 0 (no carpal motion) when compared with groups 1 (detectable motion) and 2 (palpable "clunk") combined, demonstrating the relatively high predictive value of negative scaphoid shift test findings (p < .03). Note the nearly equivalent capitate and scaphoid dorsal displacement in groups 1 and 2.
Figure 3. The midcarpal shift. During the scaphoid shift test, the capitate subluxates dorsally from the lunate fossa. The scaphoid proximal pole demonstrates predominantly axial displacement (arrow).
Scaphoid Total Displacement
Carpal Rotation
Scaphoid total displacement in group 2 was significantly greater (p < .01) than that in group 0 or in group 1 (Fig. 6). This remained highly significantly when compared to groups 0 and 1 combined (p < .01). Total scaphoid displacement correlated linearly with total capitate displacement in groups 0 and 1 (p < .01). There was no correlation between total scaphoid and capitate displacement in group 2.
A linear regression analysis comparing rotation of the scaphoid, capitate, and lunate to dorsal displacement demonstrated a statistically significant inversely proportional relationship (p values = .002, .003, .001, respectively) (Fig. 7). This inverse relationship indicates that dorsal translation was coupled with flexion, while volar translation was coupled with extension.
O~ial ~)isp i mTOtal c.~p
ml~,n~e
i
0
Figure 4. Average displacements of the scaphoid, lunate, and capitate during the scaphoid shift test on 50 uninjured wrists.
1 SId~ Grc~p
2
Figure 6. Total displacement of the carpals. Total displacement of the scaphoid in group 2 ("clunk") was significantly increased when compared with either or both of the remaining groups combined (p < .01).
The Journal of Hand Surgery / Vol. 22A No. 5 September 1997
30
2O 10
x
I X 0 9
9 o
x
.'?"~ ~ - ~ A - x 8 -~ lunate ^ ~ " X~"~/~_
ao
xol.,.. Ox @0
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o
Lunate Scaphoid I
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O
x o
x
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9
"
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0.2
0.3
-20 -30 -40
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0.4
0.5
0.6
Dorsal Displacement (RU)
Figure 7. Scatter plot demonstrating inversely proportionate relationship of scaphoid, capitate, and lunate rotation with dorsal displacement.
Discussion Our data confirmed previous observations of a high prevalence of a positive scaphoid shift in uninjured individuals. 6,7 While the "clunk" of a positive scaphoid shift has been attributed by many authors to be indicative of dorsal displacement of the scaphoid out of the scaphoid fossa, 1,3,1~ no kinematic study of this maneuver has been performed to document the actual carpal motion that occurs. In this study of 50 normal wrists, the "clunk" perceived as scaphoid dorsal subluxation in group 2 was not associated with a significant increase in dorsal displacement but indicated increased total displacement of the scaphoid from its fossa (the sum of axial and dorsal displacement). CL displacement (the midcarpal shift) appeared to be a major confounding factor in this examination. Capitate displacement from the lunate fossa was first described by Louis et al., ~2 using a provocative traction-displacement maneuver in a group of 11 patients with unexplained activity-related pain and clicking of the wrist. In this maneuver, traction was applied to the wrist while sustained dorsal pressure was applied to the scaphoid tuberosity, and fluoroscopic spots were taken in the position of maximal displacement. The capitate was seen to sublux "almost completely out of the fossa of the lunate" Simultaneous dorsal subluxation of the scaphoid and lunate from their respective fossae was described in each patient. The condition was termed CLIP (CL instability pattern)
805
wrist and was ascribed to dynamic laxity of the extrinsic ligamentous stabilizers of the scaphoid as well as to congenital or acquired laxity of the dorsal CL ligament complex. The kinematic parameter that was most closely associated with a positive scaphoid shift test in our subjects was scaphoid total displacement. Total displacement of the scaphoid was significantly increased in wrists in group 2 when compared with either remaining group or both groups combined. We believe that the "clunk" that was perceived in the group 2 patients was secondary to lifting of the scaphoid out of the scaphoid fossa of the distal radius. Fluoroscopic examination demonstrated that this occurred in subjects with true scaphoid dorsal subluxation and confirmed the findings of Louis et al. 12 that the scaphoid displaced axially out of the scaphoid fossa during the midcarpal shift as well (Fig. 3). We noted an interesting relationship between dorsal displacement and rotation of each carpal bone in response to the scaphoid shift test. Dorsal displacement of a carpal bone was associated with flexion, while those that did not shift dorsally extended. This behavior correlates well with the fluoroscopically observed "vertical" posture of the scaphoid during a positive scaphoid shift 2,3 (Fig. 8).
41'
Figure 8. Schematic demonstrating inverse relationship between dorsal subluxation and carpal bone rotation. During a true scaphoid shift (above), the bone rotates in a negative direction (flexion), while the proximal pole is displaced dorsally. In a negative shift (below), the bone rotates in the direction of the applied load (extension), while the proximal pole remains relatively stationary.
806
Wolfe et al. / Kinematics of Scaphoid Shift
In summary, our data suggest that a positive result of the scaphoid shift test be interpreted with caution, particularly when unassociated with pain during the maneuver. With 36% of uninjured wrists demonstrating a clinically positive scaphoid shift, our fluoroscopic kinematic analysis calls into question the ability to discriminate between pathologic and normal wrist conditions. While we find the scaphoid shift test to be a valuable clinical component of the decisionmaking algorithm for treatment of wrist ligament injuries, we recommend that the clinically positive scaphoid shift be confirmed fluoroscopically.
References 1. Watson HK, Ashmead D IV, Makhlouf MV. Examination of the scaphoid. J Hand Surg 1988;13A:657-660. 2. Watson HK, Ryu J, Akelman E. Limited triscaphoid intercarpal arthrodesis for rotary subluxation of the scaphoid. J Bone Joint Surg 1986;68A:345-349. 3. Taleisnik J. Scapholunate dissociation. In: The wrist. New York: Churchill Livingstone, 1985:239-278. 4. Lane LB. The scaphoid shift test. J Hand Surg 1993; 18A:366-368.
5. Wintman BI, Gelberman RH, Katz JN. Dynamic scapholuhate instability: results of operative treatment with dorsal capsulodesis. J Hand Surg 1995;20:971-979. 6. Eastefling KJ, Wolfe SW. Scaphoid shift in the uninjured wrist. J Hand Surg 1994;19A:604qS06. 7. Watson HK, Ottoni L, Pitts EC, Handal AG. Rotary subluxation of the scaphoid: a spectrum of instability. J Hand Surg 1993;18B:62~64. 8. Crisco JJ III, Wolfe SW. In vivo load displacement behavior of the carpal scaphoid ligament complex: initial measurements, time-dependence, and repeatability. In Schuind F (ed): Advances in the biomechanics of hand and wrist. New York: Plenum Press, 1993: 457--463. 9. Crisco JJ, Hentel K, Wolfe SW, Duncan JS. Two-dimensional rigid-body kinematics using image contour registration. J Biomech 1995;28:119-124. 10. Whipple TL. Intrinsic ligaments and carpal instability. In: Surgical arthroscopy. Philadelphia: JB Lippincott, 1992: 119-129. 11. Green DP. Carpal dislocations and instabilities. In: Operative hand surgery. 3rd ed. New York: Churchill Livingstone, 1993:861-928. 12. Louis DS, Hankin FM, Greene TL, Braunstein EM, White SJ. Central carpal instability----capitate lunate instability pattern. Orthopedics 1984;7:1693-1696.
As the principle link between the proximal and distal carpal rows, the scaphoid plays a critical role in coordinating and stabilizing movements of the wrist. Incomplete tears of the intrinsic or extrinsic ligaments that support the scaphoid may impair its ability to function effectively and may result in persistent pain and dysfunction with loading or activities.l-3 Such "dynamic" instability of the wrist may elude demonstration by static radiographs and may be visualized only on stress radiographs or motion studies. The scaphoid shift test has been described as a useful clinical tool in the diagnosis of dynamic
From the Yale Hand and Upper ExtremityCenter, Department of Orthopaedics and Rehabilitation,Yale UniversitySchool of Medicine, New Haven, CT, and Orthopaedic Research, Department of Orthopaedics, RhodeIsland Hospital,Providence,RI. Supportedin part by National Institutes of HealthgrantAR44005. Received for publication Feb. 13, 1996; accepted in revised form March 19, 1997. No benefitsin any form have been receivedor will be receivedfrom a commercialparty related directlyor indirectlyto the subject of this article. Reprint requests: Scott W. Wolfe, MD, Yale University School of Medicine, Department of Orthopaedics and Rehabilitation, RO. Box 208071, New Haven,CT 06520-8071.
wrist instability, particularly when it reproduces the patient's symptoms. ~,4,5 In this examination, deliberate load is applied to the scaphoid tubercle as the wrist is brought from ulnar to radial deviation, and the examiner palpates for dorsal displacement of the proximal pole of the scaphoid from the scaphoid fossa of the distal radius (Fig. 1). There is a spectrum of mobility that may occur during the maneuver, and the test results may be positive in up to one third of uninjured individuals. 6,7 The actual motion that occurs among the carpals during performance of the test has not been characterized. The purposes of this study were to determine the displacement and rotation of the scaphoid, lunate, and capitate during the "scaphoid shift test in uninjured subjects and to compare the results of the clinical examination to findings on fluoroscopic analysis.
Materials and Methods A total of 25 subjects (50 wrists) without history of prior wrist injury or dysfunction were examined in this study. Informed consent for the study was obtained per a Human Investigations Committee protocol. The modification of the scaphoid shift test as The Journal of Hand Surgery
801
[102 Wolfe et al. / Kinematics of Scaphoid Shift
A
B
Figure 1. Fluoroscopic lateral views of a scaphoid shift test performed on a patient with surgically confirmed scapholunate dissociation. (A) The wrist at rest (no load applied). (B) Maximally loaded image during the scaphoid shift test. Note the subluxation of the scaphoid onto the dorsal lip of the distal radius that occurred during application of load.
described by Lane was performed on each wrist by a single examiner. 2,4 The maneuver was repeated five times to precondition the wrist ligamentsS; grading, on a scale of 0-2, was based on the results of the fifth cycle. Zero represented no appreciable subluxation of the scaphoid. A grade of 2 represented a perceived subluxation of the scaphoid from the scaphoid fossa, with a palpable "clunk" that occurred upon release of thumb pressure. A grade of 1 was assigned to those wrists in which some carpal bone movement could be appreciated but no frank clunk or subluxation occurred. The exam was then repeated on the opposite wrist. The scaphoid shift test was repeated under fluoroscopy. A fluoroscopy unit (XiScan, XiTec, Inc., South Windsor, CT) and a video cassette recorder were peripherally attached to a personal computer; which was used as the means of collecting data. A video digitizing card (Video Spigot Pro NuBus, SuperMac Technologies, Sunnyvale, CA) was installed in the computer, allowing the user to collect and store digital images from the fluoroscope at a rate of approximately 12 frames per second. The subject was seated exactly as before, face-to-face with the examiner. The C-ann of the fluoroscope was adjusted to give a lateral view of the wrist without interfering with the examination. Several cycles of the scaphoid shift test were recorded for both the left and fight wrists for each subject.
Kinematic Analysis
The fluoroscopic tapes were reviewed and images were selected to represent the resting state (ie, the examiner was not applying pressure with his thumb) and the loaded state (the image with the maximum displacement of the carpus). For both the resting and loaded images, bony contours of the carpal bones (scaphoid, lunate, and capitate) and distal radius were digitized using MedVision software (Evergreen Technologies, Hartford, CT). The kinematic parameters of the carpal bones were calculated using a previously described contour registration technique. 9 Briefly, the two-dimensional contour of the bone can be considered a unique descriptor that is invariant to rigid body motion. This method registers or matches 2 digitized contours of the same bone at 2 different positions by quantitively matching their curvatures. The process yields a dense set of displacement vectors from which kinematic parameters (rotation and displacement) are determined. The advantage of this method is that the kinematic parameters can be accurately determined without identifying specific landmarks or surgically introducing radiopaque markers. Displacements of the scaphoid and lunate were described in reference to a radial coordinate system defined at the point of maximal curvature (point A) on the dorsal lip of the distal radius (Fig. 2). Displacements of the capitate were described in a coor-
The Journal of Hand Surgery / Vol. 22A No. 5 September 1997
Dotstl
Rotations were defined as positive if the carpal bone extended in response to the applied load and as negative if the carpal bone flexed.
Statistical Comparisons
~- Axial
7 VolarR a ~
I
D' ~T D
803
Rotation=0~
Unloaded
Displacement and rotation were compared to the results of the clinical scaphoid shift test (groups 0, 1, and 2) using a factorial (nonrepeated) analysis of variance with a post-hoc Fisher pairwise least significant difference (PLSD) test (Statview SE, Abacus Concepts, Berkeley, CA). Comparisons of kinematic parameters among different groups were performed using an unpaired, two-tailed Student's t-test. Additionally, a linear regression analysis was performed to determine the relationship between rotation of the carpal bones and their dorsal displacement.
AA
Figure 2. Calculation of scaphoid displacement in terms of radial units (RU), defined as the distance between points A and B. Point D on the scaphoid contour was defined as the point closest to the midpoint of the radial articular surface. Total displacement was the length of the displacement vector (D-D'). AT is the dorsal displacement vector; AA is the axial displacement vector. Rotation in flexion was defined as a positive rotation.
dinate system similarly defined on the dorsal lip of the lunate. Displacements were computed in terms of radial units (RU). A radial unit (RU) was defined as the distance between the vertices of the dorsal and volar lips of the distal radius. Use of RUs allowed comparison of displacement data between wrists of different sizes. To calculate displacement between resting and loaded images of the scaphoid shift test, a point (D) on the contour of the scaphoid and lunate that was closest to the midpoint between the dorsal and volar lips of the radius on the resting image was defined (Fig. 2). Using the contour registration technique, the computer was able to define the same point on the loaded image (D'). Total displacement of the bone was defined as the length of the displacement vector (D-D'). Dorsal displacement (AT) was defined as the length of the displacement vector perpendicular to the longitudinal axis of the radius. Axial displacement (AA) was defined as the length of the displacement vector parallel to the longitudinal axis of the radius.
Results Fifteen wrists (30%) had grade 0 clinical scaphoid shift, 17 wrists (34%) had a grade 1 shift, and 18 wrists (36%) had a grade 2 shift. During the fluoroscopic imaging of the scaphoid shift test, 13 of 50 wrists (26%) demonstrated dorsal subluxation of the scaphoid proximal pole over the dorsal lip of the distal radius. Of these 13 wrists, only 6 were in group 2. An unexpected finding, however, was capitate dorsal subluxation from the capitolunate (CL) joint in 13 of the remaining 37 wrists. This type of motion was referred to as a "midcarpal shift" and was not associated with appreciable dorsal displacement of the scaphoid (Fig. 3). Simultaneous axial widening of the radiolunate and radioscaphoid joints was noted during the midcarpal shift.
Calculated Carpal Displacements Displacements for the scaphoid, lunate, and capitate in the 50 wrists are displayed in Figure 4. As expected, the scaphoid exhibited substantial dorsal and total displacement; an unexpected finding was the nearly equivalent amot~nt of capitate displacement. When analyzed by group, there was no significant difference between groups 0, 1, and 2 in scaphoid dorsal displacement or rotation. Similarly, there was no significant difference of rotation or displacement of the capitate and lunate between groups 0, 1, and 2. There was a statistically significant difference in scaphoid dorsal displacement between group 0 and the other 2 groups combined (p < .03) (Fig. 5).
804
Wolfe et al. / Kinematics of Scaphoid Shift
0
1
2
8hilt @ ~ p
Figure 5. Dorsal displacement of the carpals. Dorsal displacement of the scaphoid is significantly decreased in group 0 (no carpal motion) when compared with groups 1 (detectable motion) and 2 (palpable "clunk") combined, demonstrating the relatively high predictive value of negative scaphoid shift test findings (p < .03). Note the nearly equivalent capitate and scaphoid dorsal displacement in groups 1 and 2.
Figure 3. The midcarpal shift. During the scaphoid shift test, the capitate subluxates dorsally from the lunate fossa. The scaphoid proximal pole demonstrates predominantly axial displacement (arrow).
Scaphoid Total Displacement
Carpal Rotation
Scaphoid total displacement in group 2 was significantly greater (p < .01) than that in group 0 or in group 1 (Fig. 6). This remained highly significantly when compared to groups 0 and 1 combined (p < .01). Total scaphoid displacement correlated linearly with total capitate displacement in groups 0 and 1 (p < .01). There was no correlation between total scaphoid and capitate displacement in group 2.
A linear regression analysis comparing rotation of the scaphoid, capitate, and lunate to dorsal displacement demonstrated a statistically significant inversely proportional relationship (p values = .002, .003, .001, respectively) (Fig. 7). This inverse relationship indicates that dorsal translation was coupled with flexion, while volar translation was coupled with extension.
O~ial ~)isp i mTOtal c.~p
ml~,n~e
i
0
Figure 4. Average displacements of the scaphoid, lunate, and capitate during the scaphoid shift test on 50 uninjured wrists.
1 SId~ Grc~p
2
Figure 6. Total displacement of the carpals. Total displacement of the scaphoid in group 2 ("clunk") was significantly increased when compared with either or both of the remaining groups combined (p < .01).
The Journal of Hand Surgery / Vol. 22A No. 5 September 1997
30
2O 10
x
I X 0 9
9 o
x
.'?"~ ~ - ~ A - x 8 -~ lunate ^ ~ " X~"~/~_
ao
xol.,.. Ox @0
X
o
Lunate Scaphoid I
CaDitate o
O
x o
x
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o
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0
9
"
0apitate
0.2
0.3
-20 -30 -40
i,l,l,l,l,l,l,l,l'l'l'l'l'l'l'l'l -0.2 -0.1 0.0 0.1
0.4
0.5
0.6
Dorsal Displacement (RU)
Figure 7. Scatter plot demonstrating inversely proportionate relationship of scaphoid, capitate, and lunate rotation with dorsal displacement.
Discussion Our data confirmed previous observations of a high prevalence of a positive scaphoid shift in uninjured individuals. 6,7 While the "clunk" of a positive scaphoid shift has been attributed by many authors to be indicative of dorsal displacement of the scaphoid out of the scaphoid fossa, 1,3,1~ no kinematic study of this maneuver has been performed to document the actual carpal motion that occurs. In this study of 50 normal wrists, the "clunk" perceived as scaphoid dorsal subluxation in group 2 was not associated with a significant increase in dorsal displacement but indicated increased total displacement of the scaphoid from its fossa (the sum of axial and dorsal displacement). CL displacement (the midcarpal shift) appeared to be a major confounding factor in this examination. Capitate displacement from the lunate fossa was first described by Louis et al., ~2 using a provocative traction-displacement maneuver in a group of 11 patients with unexplained activity-related pain and clicking of the wrist. In this maneuver, traction was applied to the wrist while sustained dorsal pressure was applied to the scaphoid tuberosity, and fluoroscopic spots were taken in the position of maximal displacement. The capitate was seen to sublux "almost completely out of the fossa of the lunate" Simultaneous dorsal subluxation of the scaphoid and lunate from their respective fossae was described in each patient. The condition was termed CLIP (CL instability pattern)
805
wrist and was ascribed to dynamic laxity of the extrinsic ligamentous stabilizers of the scaphoid as well as to congenital or acquired laxity of the dorsal CL ligament complex. The kinematic parameter that was most closely associated with a positive scaphoid shift test in our subjects was scaphoid total displacement. Total displacement of the scaphoid was significantly increased in wrists in group 2 when compared with either remaining group or both groups combined. We believe that the "clunk" that was perceived in the group 2 patients was secondary to lifting of the scaphoid out of the scaphoid fossa of the distal radius. Fluoroscopic examination demonstrated that this occurred in subjects with true scaphoid dorsal subluxation and confirmed the findings of Louis et al. 12 that the scaphoid displaced axially out of the scaphoid fossa during the midcarpal shift as well (Fig. 3). We noted an interesting relationship between dorsal displacement and rotation of each carpal bone in response to the scaphoid shift test. Dorsal displacement of a carpal bone was associated with flexion, while those that did not shift dorsally extended. This behavior correlates well with the fluoroscopically observed "vertical" posture of the scaphoid during a positive scaphoid shift 2,3 (Fig. 8).
41'
Figure 8. Schematic demonstrating inverse relationship between dorsal subluxation and carpal bone rotation. During a true scaphoid shift (above), the bone rotates in a negative direction (flexion), while the proximal pole is displaced dorsally. In a negative shift (below), the bone rotates in the direction of the applied load (extension), while the proximal pole remains relatively stationary.
806
Wolfe et al. / Kinematics of Scaphoid Shift
In summary, our data suggest that a positive result of the scaphoid shift test be interpreted with caution, particularly when unassociated with pain during the maneuver. With 36% of uninjured wrists demonstrating a clinically positive scaphoid shift, our fluoroscopic kinematic analysis calls into question the ability to discriminate between pathologic and normal wrist conditions. While we find the scaphoid shift test to be a valuable clinical component of the decisionmaking algorithm for treatment of wrist ligament injuries, we recommend that the clinically positive scaphoid shift be confirmed fluoroscopically.
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