- Email: [email protected]
Mechanical evaluation of the scaphoid shift test
Mechanical Evaluation of the Scaphoid Shift Test S. W. Wolfe, MD, J. J. Crisco, PhD, New Haven, CT Manipulative used clinical called
wrist injury.
of the carpal
translation
indicator
scaphoid
of ligament
of scaphoid of a dorsally
(normal)
wrists with
exhibited
a positive
decreased
Unilateral
mobility directed
clinical scaphoid
stiffness when
with
examination
shift had significantly
compared
with
subjects
especially
considerable
significance.
of the scaphoid
load at the scaphoid
ligament
hypermobility
instability,
and requires
pathologic
behavior
scaphoid
traumatic
is subjective,
the load-displacement
application
injury.
shift test is felt to represent
The test, however,
the degree quantifies
bones is an important facet of the examination of the of portions of the carpus in response to applied force is a commonly
examination
wrist. Abnormal
experience
testing.
displacement
of
to correlate
ligaments
We evaluated
mechani.cal
increased
the so-
We used an instrument
and its supporting
tubercle.
and with
during
in the context
that during
18 uninjured Subjects
who
and significantly
who did not have a shift. (J Hand Surg 1994;
19A:762-768.)
Clinical assessment of wrist stability is performed by isolating and manually displacing portions of the carpus. Increased carpal displacement in the context of wrist injury helps to confirm the diagnosis of ligament insufficiency. Watson described a provocative scaphoid shift test in which a manual load is applied by the examiner to the tubercle of the scaphoid.’ A palpable, and occasionally audible, clunk may be elicited as the scaphoid subluxes from the scaphoid fossa of the radius. Scaphoid subluxation during this test is felt to be pathognomonic of scaphoid instability, particularly when the test itself reproduces the pain. 2-5 The test is subjective and may be technically difficult to master. The pathomechanics of the positive scaphoid shift test are not well understood. Watson observed that the scaphoid shift ‘is not so much a test as a provocative maneuver. It does not offer a simple positive From the Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, New Haven, CT. Received for publication March 4, 1993: accepted in March 29. 1994. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Reprint requests: S. W. Wolfe, MD, Department of Orthopaedies and Rehabilitation, Yale University School of Medicine, 333 Cedar Street, New Haven. CT 06510. 762
The Journal
of Hand
Surgery
or negative result, but rather a variety of findings.“’ Imaging modalities, such as stress x-ray films or cineradiography, rarely help to confirm the diagnosis of dynamic scaphoid instability, which is based largely on a positive shift test and a history of wrist pain during stressful activities. Much of the ambiguity surrounding this test is due to the inability to quantitate the results and to the lack of clinical or laboratory investigations to determine its accuracy. A clinical test that could consistently and quantitatively document scaphoid mobility would be of considerable value for both in viw and in vitro ligament injury studies. The correlation between instability and the mechanical behavior of a joint has been well established in the literature. Markolf et al.’ reported a technique for quantitating mechanical parameters of the knee in V~VO using an instrumented knee “arthrometer.” They determined knee laxity and stiffness in 49 patients by quantitative load-displacement measurements and found the technique accurate and highly reproducibIe.’ The in viva measurements correlated well with previous measurements on 35 cadaveric knees.x A number of devices are available to complement clinical assessment of knee instability and are accepted as accurate techniques for quantification of ligamentous stability.‘-” We have
The Journal
applied this approach to analyze the supporting ligaments of the scaphoid. We hypothesized that a positive scaphoid shift test represents carpal ligament laxity or insufficiency. To test this hypothesis, we used an apparatus that applies a dorsally directed load to the scaphoid tubercle and records the resulting displacement, thus characterizing scaphoid mechanical behavior. Using this apparatus, our goal was to determine if there is a difference in the mechanical behavior of the scaphoid between normal subjects who, by clinical examination, have a positive scaphoid shift test, and those subjects who do not have a positive test. Materials Clinical
and Methods
Examination
We examined 18 wrists of 10 male volunteers with no prior history of wrist injury or dysfunction (mean age 32 years, range 25-37 years). Eight subjects were tested bilaterally, and two subjects unilaterally, due to previous wrist injury on the contralateral side. Nine subjects were right-hand dominant. Informed consent was obtained from each subject, and the methods were approved by the university human investigations committee. The senior author (S. W. W.) performed the scaphoid shift test as described by Watson6 on each wrist. The subject was seated comfortably across from the examiner and asked to place his flexed elbow on the examining table “as if to arm-wrestle.“ The subject’s forearm was slightly pronated for the examination. The examiner used his right hand to examine the subject’s right hand and vice versa. It was important that the subject was relaxed, and he
Figure 1. The scaphoid
is applied anteriorly
oi Hand
Surgery
/ Vol.
19A No. 5 September
1994
763
was instructed to specifically relax his forearm musculature. The subject’s wrist was held in ulnar deviation and slight extension. The examiner placed the four fingers of his examining hand on the dorsum of the radius, and his thumb anteriorly on the tubercle of the scaphoid (Fig. 1). Firm, constant force was delivered to the tubercle of the scaphoid, and the wrist moved to a radial deviated, slightly flexed position. Thumb force was then released by the examiner, and the scaphoid, if subluxed, abruptly reduced. The test was graded based on the degree of scaphoid subluxation. Both Watson and Lane reported a spectrum of findings with the maneuver.5‘6”’ A grade of 0 indicated a subject with rigid ligamentous support and no palpable translation (group 0). A + 1 shift indicated a mild generalized displacement of the carpus without a palpable subluxation of the scaphoid (group 1) (Fig. 2A,B). A + 2 shift indicated a true scaphoid subluxation from the scaphoid fossa, with a palpable, and occasionally audible clunk as the scaphoid reduced on release of force (group 2) (Fig. 2C.D). Mechanical
Evaluation
Each subject was seated comfortably with his supinated forearm positioned within the apparatus (wrist arthrometer). The forearm and wrist were strapped to a horizontal wooden platform that supported the distal portion of the radius and the metacarpals (Fig. 3). A second platform, situated over the wrist, supported a pair of linear bearings that guided the free vertical travel of a plunger. The plunger had a dimpled plastic tip to accept the scaphoid tubercle. A dorsally directed force was applied
shift test. The examiner’s fingers stabilize the dorsum of the hand while simultaneous to the tubercle of the scaphoid.
pressure
764
Wolfe
and Crisco
/ Scaphoid
Shift Te>t
Figure 2. Differences in scaphoid mobility during the manual scaphoid shift test, as shown fluoroscopically. (A,B) Lateral views of a subject in group 1, demonstrating widening of the lunocapitate joint (small arrows), but no frank scaphoid subluxation (C,D). Lateral views of the cat-pus in a subject in group 2 (positive scaphoid shift), demonstrating a true scaphoid subluxation with load (large arrow). Note simultaneous widening of radiolunate space (small arrow). to the scaphoid
tubercle via a handle at the top of the plunger. The force was recorded by a strain gauge load cell, constructed and calibrated in our laboratory. An attached personal computer audibly alerted the examiner when a maximum load of 40 N had been applied. The displacement of the plunger was recorded with a displacement transducer (1000 HR-DC, Schaevitz, Pennsauken, NJ). The computer sampled the analog signals from the load cell and displacement transducer simultaneously. Five cycles were performed for each test, and the load-displacement data was recorded and stored. Displacements were defined relative to the position at a zero load of the first cycle. The maximum displacement (mm) was defined as the greatest displacement from the zero position. The stiffness
(N/mm) was the slope of the least squares fit to the load-displacement data during the fifth cycle (MATHPAK 87, Precision Plus Software, Ontario, Canada). The position of the plunger at a zero load, relative to the first cycle, was defined as the residual displacement (mm). We report only the data of the fifth cycle, as previous work has documented a visoelastic “preconditioning” response of the scaphoid ligamentous complex to applied load during the first five cycles.r4 The clinical examination was blinded from the results of the mechanical evaluation. We analyzed the three groups for significant differences in mechanical parameters (residual displacement, maximal displacement, and stiffness). We also compared the mechanical parameters of the seven wrists with a
The Journal of Hand Surgery I
Vol.
19A
NO.
5
September 1994
765
plungerhandle
,
dlapl-t
tnnsducer
bad cell
x linear bearing guide
+-tt
wooer olatform
/
suppon platform
support platform
Figure 3. Schematic drawing of the arthrometer. Load is applied via the plunger handle. and displacement ously measured by a transducer and recorded on an attached personal computer.
Each analysis used a factorial (nonrepeated) format analysis of variance with a post hoc Fischer LSD test (Statview SE, Abacus Concepts, Berkeley, CA). A logistic regression analysis was performed to assess the ability of the examiner to predict the presence or absence of a scaphoid shift based on measured values for maximal displacement or stiffness. Sensitivity, specificity, and accuracy of the arthrometer for correct prediction of a positive scaphoid shift test were calculated for incremental values of maximal displacement and stiffness. Accuracy was corrected for chance agreement using Cohen’s Kappa analysis. Receiver operating characteristic curves were constructed by plotting true positive rates against false positive rates for each incremental increase in displacement and stiffness. Using these curves, we could choose an optimal cut2 + scaphoid
shift against
all other
~_.
wrists.
Range (mm)
SD
3.8* 6 3* s:i* 4.7% 8. I”
2.0-5.0 2.9-8.7 7.0-9.4 2.9-8.7 7.0-9.4
o.ao* 2.60* 0.80” 1.90* 0.90*
_.
off value for both displacement and stiffness to minimize overall error in prediction of the presence or absence of a positive shift.
Results There were seven wrists in group 0, four in group 1, and seven in group 2. Three subjects had asymmetric findings. with a 2+ shift on one side and a I + shift on the other. The typical results for a single test of five cycles are presented as load-displacement curves in Figure 4. Each curve demonstrated an approximately linear behavior, with a trend toward increased stiffness with increasing load, With each successive loading cycle the curves tended to shift along the displacement axis as residual and maximum displacement increased. Stiffness, however, remained similar with each cycle.
. __I_-Table 1. Mechanical
Avrrc~ge .M~LCTUU?l Dispfacrmrrt (mm)
is simultane-
Parameters
Average Stiffness (Nlmm) -. __-. 12.6* 9.1 6.5* 11.3” 6.5*
Rrmge (N/mm) 8.8-18.9 4.5-15.8 4.4-9.3 4.5-18.9 4.4-9.3
SD 3 .6OS 5.00 1.so* 4.30* I .50”
Averccge Residual Displacement (mm) 0.50 0.50 I.00 0.50 1.00
_
SD 0.40 0.20 1.00 0.30 1.00 __~.. __
766
Wolfe
and Crisco
/ Scaphoid
Shift Test
1.0
0.5
0.0
1.5
Dbflammnt
2.0
2.5
3.0
(mm)
Typical test of five cycles. Note shift of curve along displacement axis with successive cycles (residual displacement), while slope of curve (stiffness) stays relatively constant. Maximum displacement is measured (mm) at a 40 N
Figure 4.
There were significant differences in the mechanical parameters among the groups (Table 1). Maximum displacement increased significantly among each group (p < .Ol). Values for stiffness decreased successively between groups 0, 1, and 2, but showed significantly decreased stiffness only when comparing groups 0 and 2 (p = .Ol). Residual displacement was increased in group 2 as compared with the others, but it was not significant. We compared only the seven wrists with a 2+ positive scaphoid shift against all others, and the differences in maximum displacement and stiffness were highly significant (p < .Ol). When analyzed by logistic regression, both the values for maximum displacement and for stiffness were significantly predictive of the presence or absence of a scaphoid shift (p < .03). Using the receiver operating characteristic curves, we localized optimal cutoff values as 8.0 N/ mm for stiffness and 7.0 mm for maximal displace-
Table 2. Predictive
Cutoff
Stiffness 8.0 N/mm Displacement 7.0 mm
~8.0 N/m >8.0 N/m >7.0 mm <7.0 mm
Sensitivity
6
2
86%
1
9 100%
7
2
0
9
Discussion Watson has defined “dynamic rotatory subluxation of the scaphoid” as symptomatic scaphoid hyperrnobility without x-ray film evidence of abnormal carpal posture.’ Symptomatic scaphoid hypermobility is contirmed clinically by positive findings on The condition is the scaphoid shift test. 1.1.~,6,13.15.16 thought to be induced by ligamentous injury at the proximal or distal end of the scaphoid.‘.4,5,6.‘6-18 Pa-
Values for Mechanical
No shift
Shif
Valae
ment. Sensitivity, specificity, and accuracy, as well as positive and negative predictive values for these values, are shown in Table 2. By knowing the value for maximal displacement or stiffness, the examiner could accurately predict the presence or absence of a scaphoid shift with an accuracy of 83% and 89%, respectively. The accuracy of prediction remained high when corrected for chance agreement, with Kappa values of 82% and 88%, respectively.
Specificity
Measurements Positive Predictive Value
Accuracy
Kappa
82%
83%
82%
75%
82%
89%
88%
78%
Negative Predictive Value
90% 100%
The lournal
tients with dynamic scaphoid instability may be incapacitated by pain during stressful activities,’ yet an imaging workup may be entirely normal. The scaphoid shift test is difficult to master, and both Watson and Lane have stated that considerable experience is necessary to interpret the clinical findings.6,” In this investigation, we have shown that there is a measurable difference in scaphoid displacement in response to a dorsally directed load between subjects who have a positive scaphoid shift test in comparison to those without a positive scaphaid shift. The ligament stiffness is significantly decreased among subjects who demonstrate a positive scaphoid shift, indicating laxity but not necessarily pathology of carpal ligaments in this group. Measured parameters of scaphoid mechanical behavior (maximum displacement and stiffness) are accurate and predictive of the presence or absence of a clinical scaphoid shift test in uninjured subjects. As testing was performed only on uninjured wrists, this investigation may not be directly applicable to the examination of an injured wrist. The accuracy and ability of these measurements or the scaphoid shift test to predict symptomatic instability was not assessed in this study. The finding of a 2 + scaphoid shift in an asymptomatic wrist may be related to generalized ligamentous laxity and not to occult carpal injury, especially when present bilaterally. A previous study showed a 25% bilateral scaphoid shift in the uninjured population and a high correlation between the presence of an asymptomatic subluxable scaphoid and generalized ligamentous laxity, as measured by increases in wrist range of motion and thumb hyperlaxity.” Watson demonstrated a 21% unilateral scaphoid shift in 1000 randomly selected individuals and found that nearly two thirds of them had no associated symptoms or signs of clinical instability.’ For accurate diagnosis of clinical instability, it is necessary to correlate the finding of increased scaphoid mobility with symptoms of activity-related pain and local signs of synovitis.5.h.13 The reproducibility of measurements with this instrument has been addressed in a previous investigation on 16 uninjured wrists.14 After preconditioning the wrists with five loading cycles, the variance for repeated measurements of each wrist was 0.4 mm in residual displacement. 0.5 mm in the maximum displacement, and 1.8 N/mm in stiffness. Preconditioning is a well-documented phenomenon in the mechanical testing of viscoelastic tissues, and is typically associated with load-displacement curves that shift along the displacement axis with diminishing differences for successive cycles.” The apparatus directly measures scaphoid dis-
of Hand
Surgery
/ Vol.
19A No. 5 September
1994
767
placement in response to an applied load at its tubercle. This mechanical behavior is a function of the competence or laxity of the multiple intrinsic and extrinsic supporting ligaments of the scaphoid. Bony constraints of the radiocarpal and intercarpal articulations may also influence this mechanical behavior. Our present study is limited to a gross description of the mechanical behavior of the scaphoid. The relative contributions and influence of each of the supporting structures remain unclear. Quantifying scaphoid displacement in response to applied load may provide valuable information for objective evaluation of scaphoid stability. Data can be generated to study patients with various carpal injury patterns. Quantitative assessment of scaphoid mechanical behavior may allow clinical documentation of the effects of surgical reconstruction or rehabilitation on restoration of stability to the radioscaphoid joint. In vitro testing of scaphoid kinematics before and after ligament sectioning should provide insights into the pathogenesis of scaphoid instability. We would like to thank Eric Vajda, B.S. for his assistance constructing MD.
the load-displacement
for his assistance
apparatus
in analyzing
and Robert
in
Brown.
the data.
References I. Watson HK, Ryu J, Akelman
3 _.
3.
4. 5.
6. 7.
8.
9.
IO.
E. Limited triscaphoid intercarpal arthrodesis for rotary subluxation of the scaphoid. J Bone Joint Surg 1986:68A:345-9. Blatt G. In: Lichtman DM, ed. The wrist and its disorders. Philadelphia: Saunders, 1988:242-5. Green DP. Carpal dislocations and instabilities. In: Green DP, ed. Operative hand surgery. 2nd ed. New York: Churchill Livingstone. 1988:875-938. Taleisnik J. The wrist. New York: Churchill Livingstone, 1985:255-9. Watson HK, Ottoni L. Pitts EC, Handal AG. Rotary subluxation of the scaphoid: a spectrum of instability. J Hand Surg 1993;18B:62-4. Watson HK, Ashmead D. Makhlouf MV. Examination of the scaphoid. J Hand Surg 1988;13A:657-60. Markolf KL. Graff-Radford A, Amstutz HC. In vivo knee stability: a quantitative assessment using an instrumented clinical testing apparatus. J Bone Joint Surg 1978;60A:664-74. Markolf KL, Mensch JS, Amstutz HC. Stiffness and laxity of the knee: the contributions of the supporting structures-a quantitative in vitro study. J Bone Joint Surg 1976;58A:583-94. Bach BB, Warren RF. Flynn WM. Kroll M. Wichiewicz TZ. Arthrometric evaluation of knees that have a torn anterior cruciate ligament. J Bone Joint Surg 1990:72A: 1299-306. Daniel DM, Stone ML, Sachs R, Malcom L. Instrumented measurement of anterior knee laxity in pa-
768
11.
12.
13. 14.
Wolfe and Crisco / Scaphoid Shift Test tients with acute anterior cruciate ligament disruption. Am J Sports Med 1984;13:401-7. Steiner ME, Brown C, Zarins B, Brownstein B, Koval PS, Stone P. Measurement of anterior-posterior displacement of the knee. J Bone Joint Surg 1990;72A: 1307-15. Shino K, Inoue M, Horibe S, Nakamara M, Ono K. Measurement of anterior instability of the knee: a new apparatus for clinical testing. J Bone Joint Surg 1987; 69B:608-13. Lane LB. The scaphoid shift test. J Hand Surg 1993; 18A:366-8. Crisco JJ, 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 the hand and wrist. New York: Plenum Press, 1993; 457-63.
15. Taleisnik J. Wrist: anatomy, function and injury. American Academy of Orthopedic Surgeons Instructional Course Lectures. St. Louis: Mosby, 1978; 61-87. 16. Whipple TL. Arthroscopic surgery: the wrist. Philadelphia: Lippincott, 1992: 119-29. 17. Blevens AD et al. Radiocarpal articular contact characteristics with scaphoid instability. J Hand Surg 1989;14A:781-90. 18. Watson HK. Intercarpal arthrodesis. in: Green DP, ed. Operative hand surgery. 2nd ed. New York: Churchill Livingstone, 1988;143. 19. Easterling K, Wolfe SW. The scaphoid shift in the uninjured wrist. J Hand Surg 1994;19A:604-6. 20. Fung YC. Bio-viscoelastic solids. In: Biomechanics: mechanical properties of living tissue. New York: Springer-Verlag, 1981: 196-260.
wrist injury.
of the carpal
translation
indicator
scaphoid
of ligament
of scaphoid of a dorsally
(normal)
wrists with
exhibited
a positive
decreased
Unilateral
mobility directed
clinical scaphoid
stiffness when
with
examination
shift had significantly
compared
with
subjects
especially
considerable
significance.
of the scaphoid
load at the scaphoid
ligament
hypermobility
instability,
and requires
pathologic
behavior
scaphoid
traumatic
is subjective,
the load-displacement
application
injury.
shift test is felt to represent
The test, however,
the degree quantifies
bones is an important facet of the examination of the of portions of the carpus in response to applied force is a commonly
examination
wrist. Abnormal
experience
testing.
displacement
of
to correlate
ligaments
We evaluated
mechani.cal
increased
the so-
We used an instrument
and its supporting
tubercle.
and with
during
in the context
that during
18 uninjured Subjects
who
and significantly
who did not have a shift. (J Hand Surg 1994;
19A:762-768.)
Clinical assessment of wrist stability is performed by isolating and manually displacing portions of the carpus. Increased carpal displacement in the context of wrist injury helps to confirm the diagnosis of ligament insufficiency. Watson described a provocative scaphoid shift test in which a manual load is applied by the examiner to the tubercle of the scaphoid.’ A palpable, and occasionally audible, clunk may be elicited as the scaphoid subluxes from the scaphoid fossa of the radius. Scaphoid subluxation during this test is felt to be pathognomonic of scaphoid instability, particularly when the test itself reproduces the pain. 2-5 The test is subjective and may be technically difficult to master. The pathomechanics of the positive scaphoid shift test are not well understood. Watson observed that the scaphoid shift ‘is not so much a test as a provocative maneuver. It does not offer a simple positive From the Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, New Haven, CT. Received for publication March 4, 1993: accepted in March 29. 1994. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Reprint requests: S. W. Wolfe, MD, Department of Orthopaedies and Rehabilitation, Yale University School of Medicine, 333 Cedar Street, New Haven. CT 06510. 762
The Journal
of Hand
Surgery
or negative result, but rather a variety of findings.“’ Imaging modalities, such as stress x-ray films or cineradiography, rarely help to confirm the diagnosis of dynamic scaphoid instability, which is based largely on a positive shift test and a history of wrist pain during stressful activities. Much of the ambiguity surrounding this test is due to the inability to quantitate the results and to the lack of clinical or laboratory investigations to determine its accuracy. A clinical test that could consistently and quantitatively document scaphoid mobility would be of considerable value for both in viw and in vitro ligament injury studies. The correlation between instability and the mechanical behavior of a joint has been well established in the literature. Markolf et al.’ reported a technique for quantitating mechanical parameters of the knee in V~VO using an instrumented knee “arthrometer.” They determined knee laxity and stiffness in 49 patients by quantitative load-displacement measurements and found the technique accurate and highly reproducibIe.’ The in viva measurements correlated well with previous measurements on 35 cadaveric knees.x A number of devices are available to complement clinical assessment of knee instability and are accepted as accurate techniques for quantification of ligamentous stability.‘-” We have
The Journal
applied this approach to analyze the supporting ligaments of the scaphoid. We hypothesized that a positive scaphoid shift test represents carpal ligament laxity or insufficiency. To test this hypothesis, we used an apparatus that applies a dorsally directed load to the scaphoid tubercle and records the resulting displacement, thus characterizing scaphoid mechanical behavior. Using this apparatus, our goal was to determine if there is a difference in the mechanical behavior of the scaphoid between normal subjects who, by clinical examination, have a positive scaphoid shift test, and those subjects who do not have a positive test. Materials Clinical
and Methods
Examination
We examined 18 wrists of 10 male volunteers with no prior history of wrist injury or dysfunction (mean age 32 years, range 25-37 years). Eight subjects were tested bilaterally, and two subjects unilaterally, due to previous wrist injury on the contralateral side. Nine subjects were right-hand dominant. Informed consent was obtained from each subject, and the methods were approved by the university human investigations committee. The senior author (S. W. W.) performed the scaphoid shift test as described by Watson6 on each wrist. The subject was seated comfortably across from the examiner and asked to place his flexed elbow on the examining table “as if to arm-wrestle.“ The subject’s forearm was slightly pronated for the examination. The examiner used his right hand to examine the subject’s right hand and vice versa. It was important that the subject was relaxed, and he
Figure 1. The scaphoid
is applied anteriorly
oi Hand
Surgery
/ Vol.
19A No. 5 September
1994
763
was instructed to specifically relax his forearm musculature. The subject’s wrist was held in ulnar deviation and slight extension. The examiner placed the four fingers of his examining hand on the dorsum of the radius, and his thumb anteriorly on the tubercle of the scaphoid (Fig. 1). Firm, constant force was delivered to the tubercle of the scaphoid, and the wrist moved to a radial deviated, slightly flexed position. Thumb force was then released by the examiner, and the scaphoid, if subluxed, abruptly reduced. The test was graded based on the degree of scaphoid subluxation. Both Watson and Lane reported a spectrum of findings with the maneuver.5‘6”’ A grade of 0 indicated a subject with rigid ligamentous support and no palpable translation (group 0). A + 1 shift indicated a mild generalized displacement of the carpus without a palpable subluxation of the scaphoid (group 1) (Fig. 2A,B). A + 2 shift indicated a true scaphoid subluxation from the scaphoid fossa, with a palpable, and occasionally audible clunk as the scaphoid reduced on release of force (group 2) (Fig. 2C.D). Mechanical
Evaluation
Each subject was seated comfortably with his supinated forearm positioned within the apparatus (wrist arthrometer). The forearm and wrist were strapped to a horizontal wooden platform that supported the distal portion of the radius and the metacarpals (Fig. 3). A second platform, situated over the wrist, supported a pair of linear bearings that guided the free vertical travel of a plunger. The plunger had a dimpled plastic tip to accept the scaphoid tubercle. A dorsally directed force was applied
shift test. The examiner’s fingers stabilize the dorsum of the hand while simultaneous to the tubercle of the scaphoid.
pressure
764
Wolfe
and Crisco
/ Scaphoid
Shift Te>t
Figure 2. Differences in scaphoid mobility during the manual scaphoid shift test, as shown fluoroscopically. (A,B) Lateral views of a subject in group 1, demonstrating widening of the lunocapitate joint (small arrows), but no frank scaphoid subluxation (C,D). Lateral views of the cat-pus in a subject in group 2 (positive scaphoid shift), demonstrating a true scaphoid subluxation with load (large arrow). Note simultaneous widening of radiolunate space (small arrow). to the scaphoid
tubercle via a handle at the top of the plunger. The force was recorded by a strain gauge load cell, constructed and calibrated in our laboratory. An attached personal computer audibly alerted the examiner when a maximum load of 40 N had been applied. The displacement of the plunger was recorded with a displacement transducer (1000 HR-DC, Schaevitz, Pennsauken, NJ). The computer sampled the analog signals from the load cell and displacement transducer simultaneously. Five cycles were performed for each test, and the load-displacement data was recorded and stored. Displacements were defined relative to the position at a zero load of the first cycle. The maximum displacement (mm) was defined as the greatest displacement from the zero position. The stiffness
(N/mm) was the slope of the least squares fit to the load-displacement data during the fifth cycle (MATHPAK 87, Precision Plus Software, Ontario, Canada). The position of the plunger at a zero load, relative to the first cycle, was defined as the residual displacement (mm). We report only the data of the fifth cycle, as previous work has documented a visoelastic “preconditioning” response of the scaphoid ligamentous complex to applied load during the first five cycles.r4 The clinical examination was blinded from the results of the mechanical evaluation. We analyzed the three groups for significant differences in mechanical parameters (residual displacement, maximal displacement, and stiffness). We also compared the mechanical parameters of the seven wrists with a
The Journal of Hand Surgery I
Vol.
19A
NO.
5
September 1994
765
plungerhandle
,
dlapl-t
tnnsducer
bad cell
x linear bearing guide
+-tt
wooer olatform
/
suppon platform
support platform
Figure 3. Schematic drawing of the arthrometer. Load is applied via the plunger handle. and displacement ously measured by a transducer and recorded on an attached personal computer.
Each analysis used a factorial (nonrepeated) format analysis of variance with a post hoc Fischer LSD test (Statview SE, Abacus Concepts, Berkeley, CA). A logistic regression analysis was performed to assess the ability of the examiner to predict the presence or absence of a scaphoid shift based on measured values for maximal displacement or stiffness. Sensitivity, specificity, and accuracy of the arthrometer for correct prediction of a positive scaphoid shift test were calculated for incremental values of maximal displacement and stiffness. Accuracy was corrected for chance agreement using Cohen’s Kappa analysis. Receiver operating characteristic curves were constructed by plotting true positive rates against false positive rates for each incremental increase in displacement and stiffness. Using these curves, we could choose an optimal cut2 + scaphoid
shift against
all other
~_.
wrists.
Range (mm)
SD
3.8* 6 3* s:i* 4.7% 8. I”
2.0-5.0 2.9-8.7 7.0-9.4 2.9-8.7 7.0-9.4
o.ao* 2.60* 0.80” 1.90* 0.90*
_.
off value for both displacement and stiffness to minimize overall error in prediction of the presence or absence of a positive shift.
Results There were seven wrists in group 0, four in group 1, and seven in group 2. Three subjects had asymmetric findings. with a 2+ shift on one side and a I + shift on the other. The typical results for a single test of five cycles are presented as load-displacement curves in Figure 4. Each curve demonstrated an approximately linear behavior, with a trend toward increased stiffness with increasing load, With each successive loading cycle the curves tended to shift along the displacement axis as residual and maximum displacement increased. Stiffness, however, remained similar with each cycle.
. __I_-Table 1. Mechanical
Avrrc~ge .M~LCTUU?l Dispfacrmrrt (mm)
is simultane-
Parameters
Average Stiffness (Nlmm) -. __-. 12.6* 9.1 6.5* 11.3” 6.5*
Rrmge (N/mm) 8.8-18.9 4.5-15.8 4.4-9.3 4.5-18.9 4.4-9.3
SD 3 .6OS 5.00 1.so* 4.30* I .50”
Averccge Residual Displacement (mm) 0.50 0.50 I.00 0.50 1.00
_
SD 0.40 0.20 1.00 0.30 1.00 __~.. __
766
Wolfe
and Crisco
/ Scaphoid
Shift Test
1.0
0.5
0.0
1.5
Dbflammnt
2.0
2.5
3.0
(mm)
Typical test of five cycles. Note shift of curve along displacement axis with successive cycles (residual displacement), while slope of curve (stiffness) stays relatively constant. Maximum displacement is measured (mm) at a 40 N
Figure 4.
There were significant differences in the mechanical parameters among the groups (Table 1). Maximum displacement increased significantly among each group (p < .Ol). Values for stiffness decreased successively between groups 0, 1, and 2, but showed significantly decreased stiffness only when comparing groups 0 and 2 (p = .Ol). Residual displacement was increased in group 2 as compared with the others, but it was not significant. We compared only the seven wrists with a 2+ positive scaphoid shift against all others, and the differences in maximum displacement and stiffness were highly significant (p < .Ol). When analyzed by logistic regression, both the values for maximum displacement and for stiffness were significantly predictive of the presence or absence of a scaphoid shift (p < .03). Using the receiver operating characteristic curves, we localized optimal cutoff values as 8.0 N/ mm for stiffness and 7.0 mm for maximal displace-
Table 2. Predictive
Cutoff
Stiffness 8.0 N/mm Displacement 7.0 mm
~8.0 N/m >8.0 N/m >7.0 mm <7.0 mm
Sensitivity
6
2
86%
1
9 100%
7
2
0
9
Discussion Watson has defined “dynamic rotatory subluxation of the scaphoid” as symptomatic scaphoid hyperrnobility without x-ray film evidence of abnormal carpal posture.’ Symptomatic scaphoid hypermobility is contirmed clinically by positive findings on The condition is the scaphoid shift test. 1.1.~,6,13.15.16 thought to be induced by ligamentous injury at the proximal or distal end of the scaphoid.‘.4,5,6.‘6-18 Pa-
Values for Mechanical
No shift
Shif
Valae
ment. Sensitivity, specificity, and accuracy, as well as positive and negative predictive values for these values, are shown in Table 2. By knowing the value for maximal displacement or stiffness, the examiner could accurately predict the presence or absence of a scaphoid shift with an accuracy of 83% and 89%, respectively. The accuracy of prediction remained high when corrected for chance agreement, with Kappa values of 82% and 88%, respectively.
Specificity
Measurements Positive Predictive Value
Accuracy
Kappa
82%
83%
82%
75%
82%
89%
88%
78%
Negative Predictive Value
90% 100%
The lournal
tients with dynamic scaphoid instability may be incapacitated by pain during stressful activities,’ yet an imaging workup may be entirely normal. The scaphoid shift test is difficult to master, and both Watson and Lane have stated that considerable experience is necessary to interpret the clinical findings.6,” In this investigation, we have shown that there is a measurable difference in scaphoid displacement in response to a dorsally directed load between subjects who have a positive scaphoid shift test in comparison to those without a positive scaphaid shift. The ligament stiffness is significantly decreased among subjects who demonstrate a positive scaphoid shift, indicating laxity but not necessarily pathology of carpal ligaments in this group. Measured parameters of scaphoid mechanical behavior (maximum displacement and stiffness) are accurate and predictive of the presence or absence of a clinical scaphoid shift test in uninjured subjects. As testing was performed only on uninjured wrists, this investigation may not be directly applicable to the examination of an injured wrist. The accuracy and ability of these measurements or the scaphoid shift test to predict symptomatic instability was not assessed in this study. The finding of a 2 + scaphoid shift in an asymptomatic wrist may be related to generalized ligamentous laxity and not to occult carpal injury, especially when present bilaterally. A previous study showed a 25% bilateral scaphoid shift in the uninjured population and a high correlation between the presence of an asymptomatic subluxable scaphoid and generalized ligamentous laxity, as measured by increases in wrist range of motion and thumb hyperlaxity.” Watson demonstrated a 21% unilateral scaphoid shift in 1000 randomly selected individuals and found that nearly two thirds of them had no associated symptoms or signs of clinical instability.’ For accurate diagnosis of clinical instability, it is necessary to correlate the finding of increased scaphoid mobility with symptoms of activity-related pain and local signs of synovitis.5.h.13 The reproducibility of measurements with this instrument has been addressed in a previous investigation on 16 uninjured wrists.14 After preconditioning the wrists with five loading cycles, the variance for repeated measurements of each wrist was 0.4 mm in residual displacement. 0.5 mm in the maximum displacement, and 1.8 N/mm in stiffness. Preconditioning is a well-documented phenomenon in the mechanical testing of viscoelastic tissues, and is typically associated with load-displacement curves that shift along the displacement axis with diminishing differences for successive cycles.” The apparatus directly measures scaphoid dis-
of Hand
Surgery
/ Vol.
19A No. 5 September
1994
767
placement in response to an applied load at its tubercle. This mechanical behavior is a function of the competence or laxity of the multiple intrinsic and extrinsic supporting ligaments of the scaphoid. Bony constraints of the radiocarpal and intercarpal articulations may also influence this mechanical behavior. Our present study is limited to a gross description of the mechanical behavior of the scaphoid. The relative contributions and influence of each of the supporting structures remain unclear. Quantifying scaphoid displacement in response to applied load may provide valuable information for objective evaluation of scaphoid stability. Data can be generated to study patients with various carpal injury patterns. Quantitative assessment of scaphoid mechanical behavior may allow clinical documentation of the effects of surgical reconstruction or rehabilitation on restoration of stability to the radioscaphoid joint. In vitro testing of scaphoid kinematics before and after ligament sectioning should provide insights into the pathogenesis of scaphoid instability. We would like to thank Eric Vajda, B.S. for his assistance constructing MD.
the load-displacement
for his assistance
apparatus
in analyzing
and Robert
in
Brown.
the data.
References I. Watson HK, Ryu J, Akelman
3 _.
3.
4. 5.
6. 7.
8.
9.
IO.
E. Limited triscaphoid intercarpal arthrodesis for rotary subluxation of the scaphoid. J Bone Joint Surg 1986:68A:345-9. Blatt G. In: Lichtman DM, ed. The wrist and its disorders. Philadelphia: Saunders, 1988:242-5. Green DP. Carpal dislocations and instabilities. In: Green DP, ed. Operative hand surgery. 2nd ed. New York: Churchill Livingstone. 1988:875-938. Taleisnik J. The wrist. New York: Churchill Livingstone, 1985:255-9. Watson HK, Ottoni L. Pitts EC, Handal AG. Rotary subluxation of the scaphoid: a spectrum of instability. J Hand Surg 1993;18B:62-4. Watson HK, Ashmead D. Makhlouf MV. Examination of the scaphoid. J Hand Surg 1988;13A:657-60. Markolf KL. Graff-Radford A, Amstutz HC. In vivo knee stability: a quantitative assessment using an instrumented clinical testing apparatus. J Bone Joint Surg 1978;60A:664-74. Markolf KL, Mensch JS, Amstutz HC. Stiffness and laxity of the knee: the contributions of the supporting structures-a quantitative in vitro study. J Bone Joint Surg 1976;58A:583-94. Bach BB, Warren RF. Flynn WM. Kroll M. Wichiewicz TZ. Arthrometric evaluation of knees that have a torn anterior cruciate ligament. J Bone Joint Surg 1990:72A: 1299-306. Daniel DM, Stone ML, Sachs R, Malcom L. Instrumented measurement of anterior knee laxity in pa-
768
11.
12.
13. 14.
Wolfe and Crisco / Scaphoid Shift Test tients with acute anterior cruciate ligament disruption. Am J Sports Med 1984;13:401-7. Steiner ME, Brown C, Zarins B, Brownstein B, Koval PS, Stone P. Measurement of anterior-posterior displacement of the knee. J Bone Joint Surg 1990;72A: 1307-15. Shino K, Inoue M, Horibe S, Nakamara M, Ono K. Measurement of anterior instability of the knee: a new apparatus for clinical testing. J Bone Joint Surg 1987; 69B:608-13. Lane LB. The scaphoid shift test. J Hand Surg 1993; 18A:366-8. Crisco JJ, 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 the hand and wrist. New York: Plenum Press, 1993; 457-63.
15. Taleisnik J. Wrist: anatomy, function and injury. American Academy of Orthopedic Surgeons Instructional Course Lectures. St. Louis: Mosby, 1978; 61-87. 16. Whipple TL. Arthroscopic surgery: the wrist. Philadelphia: Lippincott, 1992: 119-29. 17. Blevens AD et al. Radiocarpal articular contact characteristics with scaphoid instability. J Hand Surg 1989;14A:781-90. 18. Watson HK. Intercarpal arthrodesis. in: Green DP, ed. Operative hand surgery. 2nd ed. New York: Churchill Livingstone, 1988;143. 19. Easterling K, Wolfe SW. The scaphoid shift in the uninjured wrist. J Hand Surg 1994;19A:604-6. 20. Fung YC. Bio-viscoelastic solids. In: Biomechanics: mechanical properties of living tissue. New York: Springer-Verlag, 1981: 196-260.