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The Relationship Between the Tensile and the Torsional Properties of the Native Scapholunate Ligament and Carpal Kinematics
SCIENTIFIC ARTICLE
The Relationship Between the Tensile and the Torsional Properties of the Native Scapholunate Ligament and Carpal Kinematics Eric Quan Pang, MD,* Nathan Douglass, MD,* Anthony Behn, MS,* Matthew Winterton, MD,† Michael J. Rainbow, PhD,‡ Robin N. Kamal, MD*
Purpose The purpose of this exploratory study was to examine the relationship between the tensile and the torsional properties of the native scapholunate interosseous ligament (SLIL) and kinematics of the scaphoid and lunate of an intact wrist during passive radioulnar deviation. Methods Eight fresh-frozen cadaveric specimens were transected at the elbow joint and loaded into a custom jig. Kinematic data of the scaphoid and lunate were acquired in a simulated resting condition for 3 wrist positions—neutral, 10 radial deviation, and 30 ulnar deviation—using infrared-emitting rigid body trackers. The SLIL bone-ligament-bone complex was then resected and loaded on a materials testing machine. Specimens underwent cyclic torsional and tensile testing and SLIL tensile and torsional laxity were evaluated. Correlations between scaphoid and lunate rotations and SLIL tensile and torsional properties were determined using Pearson correlation coefficients. Results Ulnar deviation of both the scaphoid and the lunate were found to decrease as the laxity of SLIL in torsion increased. In addition, the ratio of lunate flexion-extension to radialulnar deviation was found to increase with increased SLIL torsional rotation. Conclusions Our findings support the theory that there is a relationship between scapholunate kinematics and laxity at the level of the interosseous ligaments. Clinical relevance Laxity and, specifically, the tensile and torsional properties of an individual’s native SLIL should guide reconstruction using a graft material that more closely replicates the individual’s native SLIL properties. (J Hand Surg Am. 2019;-(-):1.e1-e7. Copyright Ó 2019 by the American Society for Surgery of the Hand. All rights reserved.) Key words Scapholunate, biomechanics, kinematics.
S
represents a challenging problem for surgeons. Multiple ligaments contribute to the stability of the
CAPHOLUNATE INSTABILITY
From the *Department of Orthopaedic Surgery, Stanford University, Stanford, CA; the †Department of Orthopaedic Surgery, Penn Medicine University City, Penn Musculoskeletal Center, Philadelphia, PA; and the ‡Department of Mechanical and Materials Engineering, Queen’s University, Kingston, Ontario, Canada. Received for publication September 22, 2018; accepted in revised form October 15, 2019.
scapholunate interval; however, the scapholunate interosseous ligament (SLIL) is believed to be the most critical ligament in the maintenance of the natural Corresponding author: Robin N. Kamal, MD, Department of Orthopaedic Surgery, Stanford University, 450 Broadway St., MC 6342, Redwood City, CA 94063; e-mail: rnkamal@stanford. edu. 0363-5023/19/---0001$36.00/0 https://doi.org/10.1016/j.jhsa.2019.10.024
No benefits in any form have been received or will be received related directly or indirectly to the subject of this article.
Ó 2019 ASSH
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scapholunate kinematics and is, therefore, the focus of repair and reconstruction techniques.1 Instability of the scapholunate interval leads to pathological loading of the radioscaphoid and capitolunate joints resulting in a characteristic degenerative pattern seen in scapholunate advanced collapse.2 Thus, repair or reconstruction is recommended in an effort to mitigate the progression of posttraumatic arthritis and subsequent collapse. In the setting of chronic instability, reconstruction is required because the ligament is not amenable to primary repair. Although several SLIL reconstruction techniques are described, none successfully re-creates the in vivo anatomy and function of the SLIL.3e12 As such, outcomes commonly include progression of arthritis, loss of reduction, and persistent pain.4,5,13e15 The inability to match the in vivo function of the SLIL with current reconstruction techniques contributes, at least partly, to the suboptimal outcomes following reconstruction. Part of the difficulty in restoring kinematics is that the in vivo kinematics of the carpus are not completely understood. Several theories that attempt to model carpal kinematics of the scaphoid and lunate in radioulnar deviation exist, most notably the row and column kinematic theories.16e19 No theory to date has been able to account for the complexities of carpal motion, and thus, new theories continue to emerge.16,17,20,21 Previous studies that have examined clinical measures of hand and wrist laxity and scaphoid rotation in the coronal and sagittal planes suggest there may be a relationship between laxity and carpal kinematics.20,22 Whether these in vivo relationships and external measures of laxity correspond to mechanical properties of the scapholunate ligament itself remains unknown and unstudied. Previously, the primary focus of biomechanical studies of the SLIL has focused on the 1-dimensional tensile stiffness and load to failure.23e29 However, recent studies have additionally examined the torsional properties as well.24,29,30 The relationship between SLIL structural properties and carpal kinematics, if any, remains largely unknown. We believe that normal carpal kinematics are related to the magnitude of the torsional and tensile properties of the interosseous ligaments and that improved clinical outcomes may be achieved by better replicating in vivo carpal kinematics after SLIL reconstruction. The purpose of this study was to examine the relationship between the tensile and the torsional properties of the native SLIL and the kinematics of the scaphoid and the lunate of an intact wrist during passive radioulnar deviation. We hypothesized that J Hand Surg Am.
FIGURE 1: Volar view of the experimental setyup used for wrist kinematic testing in ulnar-radial deviation.
scaphoid and lunate rotations in all 3 planes would be correlated with SLIL structural properties. MATERIALS AND METHODS Eight fresh-frozen cadaveric arms (mean age, 54 years; range, 24e69 years; 5 men, 3 women) were obtained for the study. With the understanding that our study was meant to be an exploratory in nature, we chose our sample size based on previous similar works that identified differences in degrees of carpal rotation and differences in ligamentous stiffness.23,25,26,29,31 Fluoroscopic images were acquired of the cadaveric wrists to eliminate those with carpal pathology. Specimens were transected at the elbow joint and the fingers amputated at the metacarpophalangeal joints. Specimens were dissected preserving the extensor carpi radialis longus, extensor carpi radialis brevis, abductor pollicis longus, extensor carpi ulnaris, flexor carpi ulnaris, and flexor carpi radialis tendons. The wrist was then loaded into a previously described custom jig (Fig. 1).31,32 The proximal ulna was removed to facilitate attachment to the jig. The radius and ulna were rigidly secured in neutral alignment to the base of the jig. A 3.2-mm-diameter rod was r
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inserted into the center of the distal articular surface of the third metacarpal and into the intramedullary canal. The exposed end of the rod was then inserted through a guide in the testing device that allowed for freedom of axial and rotational motion of the rod. The guide allowed for positioning of the wrist through the full range of ulnar-radial deviation. Threaded K-wires (2.4 mm diameter) were then placed through the volar cortex in the third metacarpal, radius, scaphoid, and lunate. Custom infrared-emitting rigid body trackers (weight, 12 g) (Boulder Innovation Group, Boulder, CO) were then attached to the K-wires for active motion capture during testing. Relative motion between the rigid body trackers was accurate to 0.04 mm and 0.1 (root-meansquare error). Motion-capture data were analyzed to confirm no sudden shifts in rotational data that would be observed with any unintended rotation of the rods. None were observed during testing. Kinematic data was acquired in a simulated resting condition for 3 wrist positions: neutral, 10 radial deviation, and 30 ulnar deviation. Neutral posture was tested first; however, radial and ulnar deviation positions were randomized. Simulated resting tendon tension was applied to the carpus by hanging 1.5-N weights from strings secured to the extensor carpi radialis longus, extensor carpi radialis brevis, abductor pollicis longus, extensor carpi ulnaris, flexor carpi ulnaris, and extensor carpi radials tendons.31,33 The test operator manipulated the third metacarpal rod along the guide rail to orient the specimen in each wrist position. Wrist positions were confirmed with a digital level. Three trials were performed for each test state and averaged for analysis. Marker trajectories were captured at 40 Hz. The SLIL bone complex of each wrist was then excised to allow access to the radiocarpal joint. A hand-held probe was used to acquire landmark points on the radius, third metacarpal, scaphoid, and lunate. The origins of the scaphoid and lunate were calculated as the volumetric centroid of surface points acquired on each bone. Proximal and distal landmark points were additionally acquired on the third metacarpal. The orientation of the third metacarpal was used to verify that proper ulnar and radial wrist positions were achieved during testing. The orientation of the radial coordinate system was based on previously established directions.34 The radial origin was located at the centroid of the radial midshaft. The x axis coincided with the long axis of the distal radial shaft and was defined as a line connecting the radial origin and a point on the ridge between the radioscaphoid fossa and the radiolunate fossa (midway dorsally and volarly along the ridge) (þ proximal). The y axis was defined as a line J Hand Surg Am.
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perpendicular to the radial x axis passing through radial styloid (þ radial). The z axis was calculated as the cross-product of the x and y axes. Scaphoid and lunate ulnar-radial deviation, pronation-supination, and flexion-extension were calculated for each wrist position with respect to the resting neutral state using helical axis rotation projections onto the radius-based coordinate system.35 Motions were reported as the net difference in rotational alignment between radial and ulnar deviation wrist positions. The magnitude of the ratio of net flexion-extension to net radial-ulnar deviation was also reported. After kinematic testing was completed, the tensile and torsional properties of the excised scapholunate bone-ligament-bone were examined. Briefly, the tensile and torsional properties of the native SLIL examined previously by Pang et al29 included the tensile engagement length, torsional neutral zone, peak-topeak (PtoP) tensile displacement, and PtoP rotation. The tensile engagement length was defined as the amount of ligamentous excursion from 1 to 10-N load. This range was selected to approximate the toe region of the loading curve. During tensile testing, a 50-N loading limit was selected as an estimate of the force encountered during early rehabilitation and moderately strenuous activities.36 The PtoP tensile displacement was calculated as the displacement from 1 to 50-N load. Torsional testing of the SLIL included cyclic testing of the scaphoid and lunate from 0.45-Nm flexionextension at 0.5 Hz for 500 cycles using a sinusoidal waveform. The value of 0.45 Nm was selected because it represents approximately 36% of the failure torque of the intact ligament when the scaphoid is rotated in flexion with respect to the lunate.23,30 The torsional neutral zone was defined as the amount of rotation of the scaphoid relative to the lunate during which there was negligible torque applied to the ligament. The PtoP rotation was defined as the net rotation between 0.45 Nm flexion-extension.29 Pearson correlation coefficients were calculated to determine the relationship between scaphoid and lunate net rotations during radioulnar wrist motion of each specimen and that specimen’s SLIL tensile engagement length (mm) and torsional neutral zone ( ), as well as PtoP rotation ( ) and PtoP tensile displacement (mm). Significance was set at P less than .05. RESULTS Ligamentous structural properties and carpal motion of each specimen are presented in Tables E1 to E3 (available on the Journal’s Web site at r
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FIGURE 2: Correlation between ulnar deviation of the scaphoid A and lunate B during wrist radial-to-ulnar deviation and SLIL PtoP rotation in torsion.
www.jhandsurg.org). During a wrist arc of motion from radial to ulnar deviation, the ulnar deviation of both the scaphoid (r ¼ e0.78; P < .05) (Fig. 2A) and lunate (r ¼ e0.90; P < .05) (Fig. 2B) were found to be negatively correlated to SLIL PtoP rotation in torsion. A single outlier was removed from the data set for Figure 2B. In addition, the ratio of lunate flexion-extension to radial-ulnar deviation was found to be positively correlated with SLIL PtoP rotation in torsion (r ¼ 0.73; P < .05) (Fig. 3). DISCUSSION Our findings suggest that there may be a relationship between the torsional biomechanical properties of the native SLIL and the carpal kinematics. We demonstrated that wrists with lower ranges of SLIL rotation during torsion (PtoP) exhibited more scaphoid and lunate ulnar deviation as the wrist ulnar-deviated compared with wrists with greater laxity (larger range of rotation during torsion) SLILs. This result is in line with the findings presented by Garcia-Elias et al18 and Best et al22 that wrists with lower externally measured clinical signs of ligamentous laxity exhibit relatively greater scaphoid radial-ulnar deviation through an arc of wrist radial-ulnar motion. Our study supports the theory that there is a relationship between scapholunate kinematics and laxity at the level of the interosseous ligaments. In addition, there was a significant positive correlation between the ratio of lunate flexion-extension to radioulnar deviation and the SLIL PtoP rotation. Although the lunate and scaphoid do not rotate beyond the neutral zone of the SLIL, previously defined by Pang et al29 as 29.7 6.6 , during the measured range of motion between radial deviation and ulnar deviation, we still found that specimens J Hand Surg Am.
FIGURE 3: Correlation between the ratio of lunate flexion/ extension to radial/ulnar deviation and SLIL PtoP rotation in torsion.
with a larger PtoP rotation, and thus larger neutral zone, had similarly greater relative motion in the sagittal plane than in the coronal plane. Within the range of motion tested, no rotational torque is applied to the ligament and thus this finding is unexpected.29 This may suggest that there are other factors influencing flexion-extension of the scaphoid and lunate such as their resting positions in relative flexion or extension, variations in carpal morphology, or neutral zone laxity is a surrogate for global ligamentous laxity, including other intrinsic wrist ligaments that may have greater contributions to carpal kinematics. Overall, we believe our findings further support previous studies correlating clinical laxity with carpal motion.18,22 Garcia-Elias et al18 suggest that more lax wrists have less restraint between the proximal and the distal rows, allowing for more sagittal plane motion. Conversely, they suggest that more constrained wrists r
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require greater lateral deviation of the proximal row during radioulnar deviation to compensate for the lack of sagittal plane rotation.20 Subsequently, Best et al22 correlated clinical wrist laxity with carpal motion using computed tomography to model 3-dimensional motion. They found that the scaphoid primarily rotated in the sagittal plane during radioulnar deviation; however, wrists with less clinical laxity had increased radioulnar deviation throughout a range of motion.22 Laxity has been largely described as a clinical finding20,37e40 without a biomechanical correlate at the ligamentous level until recently described by Pang et al.29 Our current study suggests a correlation between carpal motion and ligamentous laxity supporting the work by Garcia-Elias et al20 and Best et al22 that the native laxity of the ligament influences individual carpal kinematics. Where our findings suggest this relationship between ligamentous properties such as laxity and carpal motion, translating such findings to more general models of carpal motion has proven to be difficult. Several theories exist that attempt to model carpal motion; however, no single theory has been able to completely account for all the nuances of in vivo carpal kinematics.16,17,19,20 There are numerous factors that contribute to carpal motion including carpal bone morphology, ligamentous properties, and the location of the axis of rotation between the scaphoid and the lunate, which is highly variable among individuals and wrist positions.21,41 With so many factors to consider, it is difficult for any single kinematic model to be generalizable to a population of people with such a wide range of anatomical variants and ligamentous properties. Future studies should aim to explore the feasibility of more individualized reconstruction and any clinical benefit they may provide. We recognize there are several limitations to our study. As with any biomechanical model, we attempted to simulate in vivo conditions, but soft tissue dissection and resting tensions applied to ligamentous structures cannot completely simulate in vivo conditions. We used a passive model in this study, in which the operator manipulated the wrist into the desired positions. Wrist kinematics may differ in an active wrist simulator that uses muscle activation to move the wrist to desired postures.42,43 Furthermore, we limited our wrist range of motion to neutral, 10 radial deviation, and 30 ulnar deviation to standardize the comparisons made between specimens. It is possible, however, that more extreme degrees of motion could demonstrate greater effect of laxity on kinematics. In addition, we did not account for any hysteresis effect. Neutral posture was tested first; however, radial and ulnar deviation positions were J Hand Surg Am.
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randomized. Future studies should consider this aspect of carpal motion. We focus on the SLIL ligament, which is believed to be the primary stabilizer of the scapholunate interval; however, other extrinsic and intrinsic ligaments including the scaphotrapezial, radioscaphocapitate, dorsal intercarpal, and long and short radiolunate ligaments are known to contribute to SLIL stability and were not examined.1 Future studies may benefit from examining the differential contributions of other intrinsic carpal ligaments to wrist laxity. Positioning of the specimens in the jig is difficult to standardize, and small variations in position may contribute to variable amounts of flexion and extension during simulated radioulnar deviation affecting the kinematic data. Second, the sensors used for motion capture data each weigh 12 g and the influence of that weight attached to the rods on carpal motion during testing was not accounted for. We inspected the scapholunate ligament for pathology at the time of excision, but cannot comment on the existence of a previous partial injury that may have resulted in some change in the ligamentous integrity. This may be better addressed in future studies via predissection arthroscopy and quantification of the Giessler classification of each wrist. We recognize that our sample size is small and, therefore, our findings are limited by the sample of wrists that were available. There is a spectrum of laxity among wrists, and future studies should aim to better define that spectrum. Whereas our findings support a correlation between the biomechanical properties of the native SLIL and carpal kinematics, further investigation is needed to better define this relationship. Additional future studies should aim at defining the feasibility of individualized graft selection for reconstruction that more closely match the biomechanical properties of the patient’s SLIL. For example, in a patient with more global laxity, a more lax graft material may more closely match the native properties of that patient’s SLIL and, therefore, better restore the natural kinematics of the wrist and lead to improved outcomes. Given the wide variability of biomechanical properties among individuals, it remains possible that an anatomical reconstruction simply is not feasible and that techniques should focus on reconstructions that restore some of the function of the ligament regardless of restoration of the native biomechanics. Future studies should further examine any clinical relevance that such considerations may have. ACKNOWLEDGMENTS R.N.K. receives an American Foundation of Surgery of the Hand Basic Science Grant. r
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REFERENCES
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1. Short WH, Werner FW, Green JK, Sutton LG, Brutus JP. Biomechanical evaluation of the ligamentous stabilizers of the scaphoid and lunate: part III. J Hand Surg Am. 2007;32(3):297e309. 2. Tischler BT, Diaz LE, Murakami AM, et al. Scapholunate advanced collapse: a pictorial review. Insights Imaging. 2014;5(4): 407e417. 3. Gajendran VK, Peterson B, Slater RR, Szabo RM. Long-term outcomes of dorsal intercarpal ligament capsulodesis for chronic scapholunate dissociation. J Hand Surg Am. 2007;32(9): 1323e1333. 4. Garcia-Elias M, Lluch AL, Stanley JK. Three-ligament tenodesis for the treatment of scapholunate dissociation: indications and surgical technique. J Hand Surg Am. 2006;31(1):125e134. 5. Larson TB, Stern PJ. Reduction and association of the scaphoid and lunate procedure: short-term clinical and radiographic outcomes. J Hand Surg Am. 2014;39(11):2168e2174. 6. Megerle K, Bertel D, Germann G, Lehnhardt M, Hellmich S. Longterm results of dorsal intercarpal ligament capsulodesis for the treatment of chronic scapholunate instability. J Bone Joint Surg Br. 2012;94(12):1660e1665. 7. Moran SL, Cooney WP, Berger RA, Strickland J. Capsulodesis for the treatment of chronic scapholunate instability. J Hand Surg Am. 2005;30(1):16e23. 8. Nienstedt F. Treatment of static scapholunate instability with modified Brunelli tenodesis: results over 10 years. J Hand Surg Am. 2013;38(5):887e892. 9. Ross M, Loveridge J, Cutbush K, Couzens G. Scapholunate ligament reconstruction. J Wrist Surg. 2013;2(2):110e115. 10. Talwalkar SC, Edwards AT, Hayton MJ, Stilwell JH, Trail IA, Stanley JK. Results of tri-ligament tenodesis: a modified Brunelli procedure in the management of scapholunate instability. J Hand Surg Br. 2006;31(1):110e117. 11. Van Den Abbeele KL, Loh YC, Stanley JK, Trail IA. Early results of a modified Brunelli procedure for scapholunate instability. J Hand Surg Br. 1998;23(2):258e261. 12. Weiss AP. Scapholunate ligament reconstruction using a boneretinaculum-bone autograft. J Hand Surg Am. 1998;23(2): 205e215. 13. Soong M, Merrell GA, Ortmann FIV, Weiss AP. Long-term results of bone-retinaculum-bone autograft for scapholunate instability. J Hand Surg Am. 2013;38(3):504e508. 14. Bain G, Watts A, McLean J, Lee Y, Eng K. Cable-augmented, quad ligament tenodesis scapholunate reconstruction. J Wrist Surg. 2015;4(4):246e251. 15. Chabas J-F, Gay A, Valenti D, Guinard D, Legre R. Results of the modified Brunelli tenodesis for treatment of scapholunate instability: a retrospective study of 19 patients. J Hand Surg Am. 2008;33(9): 1469e1477. 16. Moojen TM, Snel JG, Ritt M, Kauer JMG, Venema HW, Bos KE. Three-dimensional carpal kinematics in vivo. Clin Biomech. 2002;17(7):506e514. 17. Sandow MJ, Fisher TJ, Howard CQ, Papas S. Unifying model of carpal mechanics based on computationally derived isometric constraints and rules-based motion—the stable central column theory. J Hand Surg Eur Vol. 2014;39(4):353e363. 18. Garcia-Elias M, Ribe M, Rodriguez J, Cots M, Casas J. Influence of joint laxity on scaphoid kinematics. J Hand Surg Br. 1995;20(3): 379e382. 19. Craigen MA, Stanley JK. Wrist kinematics. Row, column or both? J Hand Surg Br. 1995;20(2):165e170. 20. Garcia-Elias M, Pitagoras T, Gilabert-Senar A. Relationship between joint laxity and radio-ulno-carpal joint morphology. J Hand Surg Br. 2003;28(2):158e162. 21. Rainbow MJ, Wolff AL, Crisco JJ, Wolfe SW. Functional kinematics of the wrist. J Hand Surg Eur Vol. 2016;41(1):7e21.
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Appendix A TABLE E1.
SLIL Torsional and Tensile Structural Properties Torsion
Specimen Identification
Tension
Neutral Zone ( )
PtoP Rotation ( )
Engagement Length (mm)
PtoP Displacement (mm)
A
23.2
37.4
0.16
0.33
B
31.3
51.0
0.18
0.39
C
29.1
45.4
0.12
0.27
D
42.3
62.2
0.26
0.54
E
26.9
44.1
0.16
0.36
F
20.6
43.8
0.13
0.28
G
23.0
37.7
0.10
0.24
H
34.3
50.2
0.23
0.45
TABLE E2.
Scaphoid Pronation-Supination, Extension-Flexion, and Ulnar-Radial Deviation* Scaphoid Pronation-Supination ( )
Extension-Flexion ( )
Radial-Ulnar Deviation ( )
Ratio of Flexion-Extension to Radial-Ulnar Deviation
A
e4.8
10.8
e23.6
0.46
Specimen ID
B
e9.0
7.5
e12.9
0.58
C
1.2
13.4
e14.5
0.93
D
e3.8
19.5
e12.1
1.61
E
0.4
6.8
e22.6
0.30
F
e4.4
8.7
e18.2
0.47
G
e6.6
17.2
e20.2
0.85
H
3.2
11.4
e19.0
0.60
*These values were calculated for each wrist position with respect to the resting neutral state using helical axis rotation projections onto the radiusbased coordinate system. Motions were reported as the net difference in rotational alignment between the 10 radial and the 30 ulnar deviation wrist positions. The absolute value of the ratio of net flexion-extension to net radial-ulnar deviation is also reported.
TABLE E3.
Lunate Pronation-Supination, Extension-Flexion, and Ulnar-Radial Deviation* Lunate
Specimen ID A
Pronation-Supination ( )
Extension-Flexion ( )
Radial/Ulnar Deviation ( )
Ratio of Flexion-Extension to Radial-Ulnar Deviation
e6.5
14.3
e22.4
0.64
B
e6.7
3.6
e7.1
0.51
C
e3.7
18.3
e19.8
0.92
D
e4.1
23.4
e14.2
1.64
E
1.3
e0.6
e22.8
0.03
F
e2.5
11.7
e19.6
0.60
G
e4.3
8.8
e27.0
0.33
H
4.6
13.7
e18.2
0.75
*These values were calculated for each wrist position with respect to the resting neutral state using helical axis rotation projections onto the radiusbased coordinate system. Motions were reported as the net difference in rotational alignment between the 10 radial and the 30 ulnar deviation wrist positions. The absolute value of the ratio of net flexion-extension to net radial-ulnar deviation is also reported.
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The Relationship Between the Tensile and the Torsional Properties of the Native Scapholunate Ligament and Carpal Kinematics Eric Quan Pang, MD,* Nathan Douglass, MD,* Anthony Behn, MS,* Matthew Winterton, MD,† Michael J. Rainbow, PhD,‡ Robin N. Kamal, MD*
Purpose The purpose of this exploratory study was to examine the relationship between the tensile and the torsional properties of the native scapholunate interosseous ligament (SLIL) and kinematics of the scaphoid and lunate of an intact wrist during passive radioulnar deviation. Methods Eight fresh-frozen cadaveric specimens were transected at the elbow joint and loaded into a custom jig. Kinematic data of the scaphoid and lunate were acquired in a simulated resting condition for 3 wrist positions—neutral, 10 radial deviation, and 30 ulnar deviation—using infrared-emitting rigid body trackers. The SLIL bone-ligament-bone complex was then resected and loaded on a materials testing machine. Specimens underwent cyclic torsional and tensile testing and SLIL tensile and torsional laxity were evaluated. Correlations between scaphoid and lunate rotations and SLIL tensile and torsional properties were determined using Pearson correlation coefficients. Results Ulnar deviation of both the scaphoid and the lunate were found to decrease as the laxity of SLIL in torsion increased. In addition, the ratio of lunate flexion-extension to radialulnar deviation was found to increase with increased SLIL torsional rotation. Conclusions Our findings support the theory that there is a relationship between scapholunate kinematics and laxity at the level of the interosseous ligaments. Clinical relevance Laxity and, specifically, the tensile and torsional properties of an individual’s native SLIL should guide reconstruction using a graft material that more closely replicates the individual’s native SLIL properties. (J Hand Surg Am. 2019;-(-):1.e1-e7. Copyright Ó 2019 by the American Society for Surgery of the Hand. All rights reserved.) Key words Scapholunate, biomechanics, kinematics.
S
represents a challenging problem for surgeons. Multiple ligaments contribute to the stability of the
CAPHOLUNATE INSTABILITY
From the *Department of Orthopaedic Surgery, Stanford University, Stanford, CA; the †Department of Orthopaedic Surgery, Penn Medicine University City, Penn Musculoskeletal Center, Philadelphia, PA; and the ‡Department of Mechanical and Materials Engineering, Queen’s University, Kingston, Ontario, Canada. Received for publication September 22, 2018; accepted in revised form October 15, 2019.
scapholunate interval; however, the scapholunate interosseous ligament (SLIL) is believed to be the most critical ligament in the maintenance of the natural Corresponding author: Robin N. Kamal, MD, Department of Orthopaedic Surgery, Stanford University, 450 Broadway St., MC 6342, Redwood City, CA 94063; e-mail: rnkamal@stanford. edu. 0363-5023/19/---0001$36.00/0 https://doi.org/10.1016/j.jhsa.2019.10.024
No benefits in any form have been received or will be received related directly or indirectly to the subject of this article.
Ó 2019 ASSH
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scapholunate kinematics and is, therefore, the focus of repair and reconstruction techniques.1 Instability of the scapholunate interval leads to pathological loading of the radioscaphoid and capitolunate joints resulting in a characteristic degenerative pattern seen in scapholunate advanced collapse.2 Thus, repair or reconstruction is recommended in an effort to mitigate the progression of posttraumatic arthritis and subsequent collapse. In the setting of chronic instability, reconstruction is required because the ligament is not amenable to primary repair. Although several SLIL reconstruction techniques are described, none successfully re-creates the in vivo anatomy and function of the SLIL.3e12 As such, outcomes commonly include progression of arthritis, loss of reduction, and persistent pain.4,5,13e15 The inability to match the in vivo function of the SLIL with current reconstruction techniques contributes, at least partly, to the suboptimal outcomes following reconstruction. Part of the difficulty in restoring kinematics is that the in vivo kinematics of the carpus are not completely understood. Several theories that attempt to model carpal kinematics of the scaphoid and lunate in radioulnar deviation exist, most notably the row and column kinematic theories.16e19 No theory to date has been able to account for the complexities of carpal motion, and thus, new theories continue to emerge.16,17,20,21 Previous studies that have examined clinical measures of hand and wrist laxity and scaphoid rotation in the coronal and sagittal planes suggest there may be a relationship between laxity and carpal kinematics.20,22 Whether these in vivo relationships and external measures of laxity correspond to mechanical properties of the scapholunate ligament itself remains unknown and unstudied. Previously, the primary focus of biomechanical studies of the SLIL has focused on the 1-dimensional tensile stiffness and load to failure.23e29 However, recent studies have additionally examined the torsional properties as well.24,29,30 The relationship between SLIL structural properties and carpal kinematics, if any, remains largely unknown. We believe that normal carpal kinematics are related to the magnitude of the torsional and tensile properties of the interosseous ligaments and that improved clinical outcomes may be achieved by better replicating in vivo carpal kinematics after SLIL reconstruction. The purpose of this study was to examine the relationship between the tensile and the torsional properties of the native SLIL and the kinematics of the scaphoid and the lunate of an intact wrist during passive radioulnar deviation. We hypothesized that J Hand Surg Am.
FIGURE 1: Volar view of the experimental setyup used for wrist kinematic testing in ulnar-radial deviation.
scaphoid and lunate rotations in all 3 planes would be correlated with SLIL structural properties. MATERIALS AND METHODS Eight fresh-frozen cadaveric arms (mean age, 54 years; range, 24e69 years; 5 men, 3 women) were obtained for the study. With the understanding that our study was meant to be an exploratory in nature, we chose our sample size based on previous similar works that identified differences in degrees of carpal rotation and differences in ligamentous stiffness.23,25,26,29,31 Fluoroscopic images were acquired of the cadaveric wrists to eliminate those with carpal pathology. Specimens were transected at the elbow joint and the fingers amputated at the metacarpophalangeal joints. Specimens were dissected preserving the extensor carpi radialis longus, extensor carpi radialis brevis, abductor pollicis longus, extensor carpi ulnaris, flexor carpi ulnaris, and flexor carpi radialis tendons. The wrist was then loaded into a previously described custom jig (Fig. 1).31,32 The proximal ulna was removed to facilitate attachment to the jig. The radius and ulna were rigidly secured in neutral alignment to the base of the jig. A 3.2-mm-diameter rod was r
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inserted into the center of the distal articular surface of the third metacarpal and into the intramedullary canal. The exposed end of the rod was then inserted through a guide in the testing device that allowed for freedom of axial and rotational motion of the rod. The guide allowed for positioning of the wrist through the full range of ulnar-radial deviation. Threaded K-wires (2.4 mm diameter) were then placed through the volar cortex in the third metacarpal, radius, scaphoid, and lunate. Custom infrared-emitting rigid body trackers (weight, 12 g) (Boulder Innovation Group, Boulder, CO) were then attached to the K-wires for active motion capture during testing. Relative motion between the rigid body trackers was accurate to 0.04 mm and 0.1 (root-meansquare error). Motion-capture data were analyzed to confirm no sudden shifts in rotational data that would be observed with any unintended rotation of the rods. None were observed during testing. Kinematic data was acquired in a simulated resting condition for 3 wrist positions: neutral, 10 radial deviation, and 30 ulnar deviation. Neutral posture was tested first; however, radial and ulnar deviation positions were randomized. Simulated resting tendon tension was applied to the carpus by hanging 1.5-N weights from strings secured to the extensor carpi radialis longus, extensor carpi radialis brevis, abductor pollicis longus, extensor carpi ulnaris, flexor carpi ulnaris, and extensor carpi radials tendons.31,33 The test operator manipulated the third metacarpal rod along the guide rail to orient the specimen in each wrist position. Wrist positions were confirmed with a digital level. Three trials were performed for each test state and averaged for analysis. Marker trajectories were captured at 40 Hz. The SLIL bone complex of each wrist was then excised to allow access to the radiocarpal joint. A hand-held probe was used to acquire landmark points on the radius, third metacarpal, scaphoid, and lunate. The origins of the scaphoid and lunate were calculated as the volumetric centroid of surface points acquired on each bone. Proximal and distal landmark points were additionally acquired on the third metacarpal. The orientation of the third metacarpal was used to verify that proper ulnar and radial wrist positions were achieved during testing. The orientation of the radial coordinate system was based on previously established directions.34 The radial origin was located at the centroid of the radial midshaft. The x axis coincided with the long axis of the distal radial shaft and was defined as a line connecting the radial origin and a point on the ridge between the radioscaphoid fossa and the radiolunate fossa (midway dorsally and volarly along the ridge) (þ proximal). The y axis was defined as a line J Hand Surg Am.
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perpendicular to the radial x axis passing through radial styloid (þ radial). The z axis was calculated as the cross-product of the x and y axes. Scaphoid and lunate ulnar-radial deviation, pronation-supination, and flexion-extension were calculated for each wrist position with respect to the resting neutral state using helical axis rotation projections onto the radius-based coordinate system.35 Motions were reported as the net difference in rotational alignment between radial and ulnar deviation wrist positions. The magnitude of the ratio of net flexion-extension to net radial-ulnar deviation was also reported. After kinematic testing was completed, the tensile and torsional properties of the excised scapholunate bone-ligament-bone were examined. Briefly, the tensile and torsional properties of the native SLIL examined previously by Pang et al29 included the tensile engagement length, torsional neutral zone, peak-topeak (PtoP) tensile displacement, and PtoP rotation. The tensile engagement length was defined as the amount of ligamentous excursion from 1 to 10-N load. This range was selected to approximate the toe region of the loading curve. During tensile testing, a 50-N loading limit was selected as an estimate of the force encountered during early rehabilitation and moderately strenuous activities.36 The PtoP tensile displacement was calculated as the displacement from 1 to 50-N load. Torsional testing of the SLIL included cyclic testing of the scaphoid and lunate from 0.45-Nm flexionextension at 0.5 Hz for 500 cycles using a sinusoidal waveform. The value of 0.45 Nm was selected because it represents approximately 36% of the failure torque of the intact ligament when the scaphoid is rotated in flexion with respect to the lunate.23,30 The torsional neutral zone was defined as the amount of rotation of the scaphoid relative to the lunate during which there was negligible torque applied to the ligament. The PtoP rotation was defined as the net rotation between 0.45 Nm flexion-extension.29 Pearson correlation coefficients were calculated to determine the relationship between scaphoid and lunate net rotations during radioulnar wrist motion of each specimen and that specimen’s SLIL tensile engagement length (mm) and torsional neutral zone ( ), as well as PtoP rotation ( ) and PtoP tensile displacement (mm). Significance was set at P less than .05. RESULTS Ligamentous structural properties and carpal motion of each specimen are presented in Tables E1 to E3 (available on the Journal’s Web site at r
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FIGURE 2: Correlation between ulnar deviation of the scaphoid A and lunate B during wrist radial-to-ulnar deviation and SLIL PtoP rotation in torsion.
www.jhandsurg.org). During a wrist arc of motion from radial to ulnar deviation, the ulnar deviation of both the scaphoid (r ¼ e0.78; P < .05) (Fig. 2A) and lunate (r ¼ e0.90; P < .05) (Fig. 2B) were found to be negatively correlated to SLIL PtoP rotation in torsion. A single outlier was removed from the data set for Figure 2B. In addition, the ratio of lunate flexion-extension to radial-ulnar deviation was found to be positively correlated with SLIL PtoP rotation in torsion (r ¼ 0.73; P < .05) (Fig. 3). DISCUSSION Our findings suggest that there may be a relationship between the torsional biomechanical properties of the native SLIL and the carpal kinematics. We demonstrated that wrists with lower ranges of SLIL rotation during torsion (PtoP) exhibited more scaphoid and lunate ulnar deviation as the wrist ulnar-deviated compared with wrists with greater laxity (larger range of rotation during torsion) SLILs. This result is in line with the findings presented by Garcia-Elias et al18 and Best et al22 that wrists with lower externally measured clinical signs of ligamentous laxity exhibit relatively greater scaphoid radial-ulnar deviation through an arc of wrist radial-ulnar motion. Our study supports the theory that there is a relationship between scapholunate kinematics and laxity at the level of the interosseous ligaments. In addition, there was a significant positive correlation between the ratio of lunate flexion-extension to radioulnar deviation and the SLIL PtoP rotation. Although the lunate and scaphoid do not rotate beyond the neutral zone of the SLIL, previously defined by Pang et al29 as 29.7 6.6 , during the measured range of motion between radial deviation and ulnar deviation, we still found that specimens J Hand Surg Am.
FIGURE 3: Correlation between the ratio of lunate flexion/ extension to radial/ulnar deviation and SLIL PtoP rotation in torsion.
with a larger PtoP rotation, and thus larger neutral zone, had similarly greater relative motion in the sagittal plane than in the coronal plane. Within the range of motion tested, no rotational torque is applied to the ligament and thus this finding is unexpected.29 This may suggest that there are other factors influencing flexion-extension of the scaphoid and lunate such as their resting positions in relative flexion or extension, variations in carpal morphology, or neutral zone laxity is a surrogate for global ligamentous laxity, including other intrinsic wrist ligaments that may have greater contributions to carpal kinematics. Overall, we believe our findings further support previous studies correlating clinical laxity with carpal motion.18,22 Garcia-Elias et al18 suggest that more lax wrists have less restraint between the proximal and the distal rows, allowing for more sagittal plane motion. Conversely, they suggest that more constrained wrists r
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require greater lateral deviation of the proximal row during radioulnar deviation to compensate for the lack of sagittal plane rotation.20 Subsequently, Best et al22 correlated clinical wrist laxity with carpal motion using computed tomography to model 3-dimensional motion. They found that the scaphoid primarily rotated in the sagittal plane during radioulnar deviation; however, wrists with less clinical laxity had increased radioulnar deviation throughout a range of motion.22 Laxity has been largely described as a clinical finding20,37e40 without a biomechanical correlate at the ligamentous level until recently described by Pang et al.29 Our current study suggests a correlation between carpal motion and ligamentous laxity supporting the work by Garcia-Elias et al20 and Best et al22 that the native laxity of the ligament influences individual carpal kinematics. Where our findings suggest this relationship between ligamentous properties such as laxity and carpal motion, translating such findings to more general models of carpal motion has proven to be difficult. Several theories exist that attempt to model carpal motion; however, no single theory has been able to completely account for all the nuances of in vivo carpal kinematics.16,17,19,20 There are numerous factors that contribute to carpal motion including carpal bone morphology, ligamentous properties, and the location of the axis of rotation between the scaphoid and the lunate, which is highly variable among individuals and wrist positions.21,41 With so many factors to consider, it is difficult for any single kinematic model to be generalizable to a population of people with such a wide range of anatomical variants and ligamentous properties. Future studies should aim to explore the feasibility of more individualized reconstruction and any clinical benefit they may provide. We recognize there are several limitations to our study. As with any biomechanical model, we attempted to simulate in vivo conditions, but soft tissue dissection and resting tensions applied to ligamentous structures cannot completely simulate in vivo conditions. We used a passive model in this study, in which the operator manipulated the wrist into the desired positions. Wrist kinematics may differ in an active wrist simulator that uses muscle activation to move the wrist to desired postures.42,43 Furthermore, we limited our wrist range of motion to neutral, 10 radial deviation, and 30 ulnar deviation to standardize the comparisons made between specimens. It is possible, however, that more extreme degrees of motion could demonstrate greater effect of laxity on kinematics. In addition, we did not account for any hysteresis effect. Neutral posture was tested first; however, radial and ulnar deviation positions were J Hand Surg Am.
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randomized. Future studies should consider this aspect of carpal motion. We focus on the SLIL ligament, which is believed to be the primary stabilizer of the scapholunate interval; however, other extrinsic and intrinsic ligaments including the scaphotrapezial, radioscaphocapitate, dorsal intercarpal, and long and short radiolunate ligaments are known to contribute to SLIL stability and were not examined.1 Future studies may benefit from examining the differential contributions of other intrinsic carpal ligaments to wrist laxity. Positioning of the specimens in the jig is difficult to standardize, and small variations in position may contribute to variable amounts of flexion and extension during simulated radioulnar deviation affecting the kinematic data. Second, the sensors used for motion capture data each weigh 12 g and the influence of that weight attached to the rods on carpal motion during testing was not accounted for. We inspected the scapholunate ligament for pathology at the time of excision, but cannot comment on the existence of a previous partial injury that may have resulted in some change in the ligamentous integrity. This may be better addressed in future studies via predissection arthroscopy and quantification of the Giessler classification of each wrist. We recognize that our sample size is small and, therefore, our findings are limited by the sample of wrists that were available. There is a spectrum of laxity among wrists, and future studies should aim to better define that spectrum. Whereas our findings support a correlation between the biomechanical properties of the native SLIL and carpal kinematics, further investigation is needed to better define this relationship. Additional future studies should aim at defining the feasibility of individualized graft selection for reconstruction that more closely match the biomechanical properties of the patient’s SLIL. For example, in a patient with more global laxity, a more lax graft material may more closely match the native properties of that patient’s SLIL and, therefore, better restore the natural kinematics of the wrist and lead to improved outcomes. Given the wide variability of biomechanical properties among individuals, it remains possible that an anatomical reconstruction simply is not feasible and that techniques should focus on reconstructions that restore some of the function of the ligament regardless of restoration of the native biomechanics. Future studies should further examine any clinical relevance that such considerations may have. ACKNOWLEDGMENTS R.N.K. receives an American Foundation of Surgery of the Hand Basic Science Grant. r
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REFERENCES
22. Best GM, Zec ML, Pichora DR, Kamal RN, Rainbow MJ. Does wrist laxity influence three-dimensional carpal bone motion? J Biomech Eng. 2018;140(4):041007. 23. Berger RA, Imeada T, Berglund L, An K-N. Constraint and material properties of the subregions of the scapholunate interosseous ligament. J Hand Surg Am. 1999;24(5):953e962. 24. Davis C, Culp R, Hume E, Osterman A. Reconstruction of the scapholunate ligament in a cadaver model using a bone-ligament-bone autograft from the foot. J Hand Surg Am. 1998;23(5):884e892. 25. Harvey EJ, Hanel D, Knight JB, Tencer AF. Autograft replacements for the scapholunate ligament: a biomechanical comparison of handbased autografts. J Hand Surg Am. 1999;24(5):963e967. 26. Johnston JD, Small CF, Bouxsein ML, Pichora DR. Mechanical properties of the scapholunate ligament correlate with bone mineral density measurements of the hand. J Orthop Res. 2004;22(4):867e871. 27. Pin P, Nowak M, Logan S, Young V, Gilula L, Weeks P. Coincident rupture of the scapholunate and lunotriquetral ligaments without perilunate dislocation- pathomechanics and management. J Hand Surg Am. 1990;15(1):110e119. 28. Svoboda SJ, Eglseder WA, Belkoff SM. Autografts from the foot for reconstruction of the scapholunate interosseous ligament. J Hand Surg Am. 1995;20(6):980e985. 29. Pang EQ, Douglass N, Behn A, Winterton M, Rainbow MJ, Kamal RN. Tensile and torsional structural properties of the native scapholunate ligament. J Hand Surg Am. 2018;43(9):864.e1e864.e7. 30. Zdero R, Olsen M, Elfatori S, et al. Linear and torsional mechanical characteristics of intact and reconstructed scapholunate ligaments. J Biomech Eng. 2009;131(4):041009. 31. Kamal RN, Chehata A, Rainbow MJ, Llusá M, Garcia-Elias M. The effect of the dorsal intercarpal ligament on lunate extension after distal scaphoid excision. J Hand Surg Am. 2012;37(11):2240e2245. 32. Salvà-Coll G, Garcia-Elias M, Llusá-Pérez M, Rodríguez-Baeza A. The role of the flexor carpi radialis muscle in scapholunate instability. J Hand Surg Am. 2011;36(1):31e36. 33. Kobayashi M, Garcia-Elias M, Nagy L, et al. Axial loading induces rotation of the proximal carpal row bones around unique screwdisplacement axes. J Biomech. 1997;30(11e12):1165e1167. 34. Coburn JC, Upal MA, Crisco JJ. Coordinate systems for the carpal bones of the wrist. J Biomech. 2007;40(1):203e209. 35. Spoor CW, Veldpaus FE. Rigid body motion calculated from spatial co-ordinates of markers. J Biomech. 1980;13(4):391e393. 36. Dimitris C, Werner FW, Joyce DA, Harley BJ. Force in the scapholunate interosseous ligament during active wrist motion. J Hand Surg Am. 2015;40(8):1525e1533. 37. Beighton PH, Solomon L, Soskolne CL. Articular mobility in an African population. Ann Rheum Dis. 1973;32(5):413. 38. Bin Abd Razak HR, Bin Ali N, Howe TS. Generalized ligamentous laxity may be a predisposing factor for musculoskeletal injuries. J Sci Med Sport. 2014;17(5):474e478. 39. Kraus VB, Li Y-J, Martin ER, et al. Articular hypermobility is a protective factor for hand osteoarthritis. Arthritis Rheum. 2004;50(7): 2178e2183. 40. Hinton R, Rivera V, Pautz M, Sponseller P. Ligamentous laxity of the knee during childhood and adolescence. J Pediatr Orthop. 2008;28(2):184e187. 41. Best GM, Mack ZE, Pichora DR, Crisco JJ, Kamal RN, Rainbow MJ. Differences in the rotation axes of the scapholunate joint during flexion-extension and radial-ulnar deviation motions. J Hand Surg Am. 2019;44(9):772e778. 42. Isa AD, McGregor ME, Padmore CE, et al. Effect of radial lengthening on distal forearm loading following simulated in vitro radial shortening during simulated dynamic wrist motion. J Hand Surg Am. 2019;44(7):556e563.e5. 43. Isa AD, Mcgregor ME, Padmore CE, et al. An in vitro study to determine the effect of ulnar shortening on distal forearm loading during wrist and forearm motion: implications in the treatment of ulnocarpal impaction. J Hand Surg Am. 2019;44(8):669e679.
1. Short WH, Werner FW, Green JK, Sutton LG, Brutus JP. Biomechanical evaluation of the ligamentous stabilizers of the scaphoid and lunate: part III. J Hand Surg Am. 2007;32(3):297e309. 2. Tischler BT, Diaz LE, Murakami AM, et al. Scapholunate advanced collapse: a pictorial review. Insights Imaging. 2014;5(4): 407e417. 3. Gajendran VK, Peterson B, Slater RR, Szabo RM. Long-term outcomes of dorsal intercarpal ligament capsulodesis for chronic scapholunate dissociation. J Hand Surg Am. 2007;32(9): 1323e1333. 4. Garcia-Elias M, Lluch AL, Stanley JK. Three-ligament tenodesis for the treatment of scapholunate dissociation: indications and surgical technique. J Hand Surg Am. 2006;31(1):125e134. 5. Larson TB, Stern PJ. Reduction and association of the scaphoid and lunate procedure: short-term clinical and radiographic outcomes. J Hand Surg Am. 2014;39(11):2168e2174. 6. Megerle K, Bertel D, Germann G, Lehnhardt M, Hellmich S. Longterm results of dorsal intercarpal ligament capsulodesis for the treatment of chronic scapholunate instability. J Bone Joint Surg Br. 2012;94(12):1660e1665. 7. Moran SL, Cooney WP, Berger RA, Strickland J. Capsulodesis for the treatment of chronic scapholunate instability. J Hand Surg Am. 2005;30(1):16e23. 8. Nienstedt F. Treatment of static scapholunate instability with modified Brunelli tenodesis: results over 10 years. J Hand Surg Am. 2013;38(5):887e892. 9. Ross M, Loveridge J, Cutbush K, Couzens G. Scapholunate ligament reconstruction. J Wrist Surg. 2013;2(2):110e115. 10. Talwalkar SC, Edwards AT, Hayton MJ, Stilwell JH, Trail IA, Stanley JK. Results of tri-ligament tenodesis: a modified Brunelli procedure in the management of scapholunate instability. J Hand Surg Br. 2006;31(1):110e117. 11. Van Den Abbeele KL, Loh YC, Stanley JK, Trail IA. Early results of a modified Brunelli procedure for scapholunate instability. J Hand Surg Br. 1998;23(2):258e261. 12. Weiss AP. Scapholunate ligament reconstruction using a boneretinaculum-bone autograft. J Hand Surg Am. 1998;23(2): 205e215. 13. Soong M, Merrell GA, Ortmann FIV, Weiss AP. Long-term results of bone-retinaculum-bone autograft for scapholunate instability. J Hand Surg Am. 2013;38(3):504e508. 14. Bain G, Watts A, McLean J, Lee Y, Eng K. Cable-augmented, quad ligament tenodesis scapholunate reconstruction. J Wrist Surg. 2015;4(4):246e251. 15. Chabas J-F, Gay A, Valenti D, Guinard D, Legre R. Results of the modified Brunelli tenodesis for treatment of scapholunate instability: a retrospective study of 19 patients. J Hand Surg Am. 2008;33(9): 1469e1477. 16. Moojen TM, Snel JG, Ritt M, Kauer JMG, Venema HW, Bos KE. Three-dimensional carpal kinematics in vivo. Clin Biomech. 2002;17(7):506e514. 17. Sandow MJ, Fisher TJ, Howard CQ, Papas S. Unifying model of carpal mechanics based on computationally derived isometric constraints and rules-based motion—the stable central column theory. J Hand Surg Eur Vol. 2014;39(4):353e363. 18. Garcia-Elias M, Ribe M, Rodriguez J, Cots M, Casas J. Influence of joint laxity on scaphoid kinematics. J Hand Surg Br. 1995;20(3): 379e382. 19. Craigen MA, Stanley JK. Wrist kinematics. Row, column or both? J Hand Surg Br. 1995;20(2):165e170. 20. Garcia-Elias M, Pitagoras T, Gilabert-Senar A. Relationship between joint laxity and radio-ulno-carpal joint morphology. J Hand Surg Br. 2003;28(2):158e162. 21. Rainbow MJ, Wolff AL, Crisco JJ, Wolfe SW. Functional kinematics of the wrist. J Hand Surg Eur Vol. 2016;41(1):7e21.
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Appendix A TABLE E1.
SLIL Torsional and Tensile Structural Properties Torsion
Specimen Identification
Tension
Neutral Zone ( )
PtoP Rotation ( )
Engagement Length (mm)
PtoP Displacement (mm)
A
23.2
37.4
0.16
0.33
B
31.3
51.0
0.18
0.39
C
29.1
45.4
0.12
0.27
D
42.3
62.2
0.26
0.54
E
26.9
44.1
0.16
0.36
F
20.6
43.8
0.13
0.28
G
23.0
37.7
0.10
0.24
H
34.3
50.2
0.23
0.45
TABLE E2.
Scaphoid Pronation-Supination, Extension-Flexion, and Ulnar-Radial Deviation* Scaphoid Pronation-Supination ( )
Extension-Flexion ( )
Radial-Ulnar Deviation ( )
Ratio of Flexion-Extension to Radial-Ulnar Deviation
A
e4.8
10.8
e23.6
0.46
Specimen ID
B
e9.0
7.5
e12.9
0.58
C
1.2
13.4
e14.5
0.93
D
e3.8
19.5
e12.1
1.61
E
0.4
6.8
e22.6
0.30
F
e4.4
8.7
e18.2
0.47
G
e6.6
17.2
e20.2
0.85
H
3.2
11.4
e19.0
0.60
*These values were calculated for each wrist position with respect to the resting neutral state using helical axis rotation projections onto the radiusbased coordinate system. Motions were reported as the net difference in rotational alignment between the 10 radial and the 30 ulnar deviation wrist positions. The absolute value of the ratio of net flexion-extension to net radial-ulnar deviation is also reported.
TABLE E3.
Lunate Pronation-Supination, Extension-Flexion, and Ulnar-Radial Deviation* Lunate
Specimen ID A
Pronation-Supination ( )
Extension-Flexion ( )
Radial/Ulnar Deviation ( )
Ratio of Flexion-Extension to Radial-Ulnar Deviation
e6.5
14.3
e22.4
0.64
B
e6.7
3.6
e7.1
0.51
C
e3.7
18.3
e19.8
0.92
D
e4.1
23.4
e14.2
1.64
E
1.3
e0.6
e22.8
0.03
F
e2.5
11.7
e19.6
0.60
G
e4.3
8.8
e27.0
0.33
H
4.6
13.7
e18.2
0.75
*These values were calculated for each wrist position with respect to the resting neutral state using helical axis rotation projections onto the radiusbased coordinate system. Motions were reported as the net difference in rotational alignment between the 10 radial and the 30 ulnar deviation wrist positions. The absolute value of the ratio of net flexion-extension to net radial-ulnar deviation is also reported.
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