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Scaphoid and lunate motion during a wrist dart throw motion1, 2
Scaphoid and Lunate Motion During a Wrist Dart Throw Motion Frederick W. Werner, MME, Jason K. Green, BS, Walter H. Short, MD, Shunji Masaoka, MD, Syracuse, NY
Purpose: The primary purpose of this study was to measure the in vitro scaphoid and lunate motion during 9 different variations of a wrist dart throw motion. Another goal was to determine the specific dart throw motion that minimized scaphoid and lunate motion. Methods: Scaphoid and lunate motion were recorded in 7 cadaver forearms during various combinations of wrist dart throw motions caused by a wrist joint motion simulator. Results: During wrist flexion and extension the scaphoid and lunate motions follow the wrist motion. During wrist radial and ulnar deviation the scaphoid and lunate correspondingly flex and extend. During intermediate motions the scaphoid and lunate move as little as 26% of the total third metacarpal motion and do not necessarily follow a planar motion. Conclusions: These findings suggest that there may be a dart throw motion during which there may be minimal scaphoid and lunate motion. If a subject’s wrist motion could be clinically restricted to this dart throw motion, early hand mobility might be possible after surgery on the scaphoid and lunate. (J Hand Surg 2004;29A:418 – 422. Copyright © 2004 by the American Society for Surgery of the Hand.) Key words: Carpal motion, wrist dart throw.
Many activities of daily living require a motion that is a combination of wrist flexion/extension and radial/ulnar deviation.1 This is referred to as a wrist
From the Department of Orthopedic Surgery, Institute for Human Performance, State University of New York Upstate Medical University, Syracuse, NY. Received for publication July 23, 2003; accepted in revised form January 27, 2004. Supported by extramural research from the National Center for Injury Prevention and Control grant number R49/CCR216814-03 from the Centers for Disease Control and Prevention, and by the National Institutes for Health grant 1R01 AR50099-01. 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. The contents of this article are solely the responsibility of the authors and do not necessarily represent the official views of the Center for Disease Control and Prevention or the National Institutes of Health. Reprint requests: Frederick W. Werner, MME, Department of Orthopedic Surgery, Institute for Human Performance, SUNY Upstate Medical University, 750 E. Adams St, Syracuse, NY 13210. Copyright © 2004 by the American Society for Surgery of the Hand 0363-5023/04/29A03-0013$30.00/0 doi:10.1016/j.jhsa.2004.01.018
418
The Journal of Hand Surgery
dart throw motion. The act of throwing a dart requires an arc of motion starting in wrist extension and radial deviation moving to wrist flexion and ulnar deviation. This requires moving the wrist in a complex 2-dimensional motion. The majority of in vivo and in vitro kinematic data for the wrist carpals have been measured during pure or quasipure wrist flexion/extension or wrist radial/ulnar deviation.2–9 In one study10 scaphoid and lunate motion were measured for one dart throw motion from 20° of extension and 10° of radial deviation to 20° of flexion and 10° of ulnar deviation. It has been suggested (Marc Garcia-Elias, personal communication, June 2001) that there may be a specific wrist dart throw motion during which there is minimal scaphoid or lunate motion. This study measured the in vitro scaphoid and lunate motion during 9 different variations of a wrist dart throw motion. The purpose of this study was to determine the specific dart throw plane of motion that minimized scaphoid and lunate motion.
Werner et al / Carpal Motion During a Dart Throw
Figure 1. Nine dart throw wrist motions studied as viewed in the transverse plane. Motion A is a pure extension to flexion motion. Motion I is a pure radial deviation to ulnar deviation. The other 7 motions were as the wrist moved from extension and radial deviation to flexion and ulnar deviation. The length of each line corresponds to the excursion of the motion.
Materials and Methods Seven fresh normal cadaver forearms were prepared for use in a wrist joint servohydraulic motion simulator in a manner similar to that used in previously published studies.9,11 The average age of the specimens was 66 years. There was 1 male and 6 female specimens. There were 4 specimens with a type 1 lunate and 3 specimens with a type 2 lunate. Each forearm was determined by fluoroscopy and arthroscopic examination to be free of traumatic and systemic defects. The major wrist tendons (extensor carpi ulnaris, extensor carpi radialis brevis, extensor carpi radialis longus, abductor pollicis longus, flexor carpi radialis, and flexor carpi ulnaris) were kept intact for the attachment of the corresponding hydraulic actuators in the wrist simulator.12 All capsular and retinacular structures were spared. Physiologic tendon loading was used to cause 9 variations of wrist motion (Fig. 1). The motions ranged from a cyclic flexion/extension motion (30° extension to 30° flexion, with 0° of radial/ulnar deviation; Fig. 1, motion A), to 7 dart throw motions in which the wrist moved from wrist extension and radial deviation to flexion and ulnar deviation (motions B, C, D, E, F, G, H), and finally to a pure radial/ulnar deviation motion (10° radial deviation to 20° ulnar deviation, with 0° of flexion/extension; motion I).
419
Sensors (Fastrak; Polhemus, Colchester, VT) (Fig. 2) were attached11 indirectly to the scaphoid and lunate, and directly to the third metacarpal whose motion was defined to be equivalent to wrist motion (based on the International Society for Biomechanics proposed standard definition for the wrist and hand joint coordinate systems; http://www.isbweb.org/ standards/wrist.html). The sensors for the scaphoid and lunate were mounted onto acrylic platforms that were glued onto pultruded carbon fiber rods. The rods were inserted and cemented into 2.7-mm unicortical drill holes in each bone. During each cyclic motion these sensors measured the 3-dimensional motion of these bones relative to electromagnetic sources mounted onto the ulna, with an accuracy of 0.2° and 0.2 mm.9 An agonist-antagonist muscle tendon load algorithm was used to control wrist motion based on the third metacarpal motion data. This algorithm has been shown to maintain an actual wrist flexion/extension motion to within 1° of a pure planar motion (ie, there was less than 1° change from neutral radial/ulnar deviation during a pure flexion/ extension motion).9 This method permitted fine control of wrist motion and allowed clear differentiation between different dart throw motions that could not be possible in vivo without exterior guidance to the wrist. Scaphoid and lunate motion were analyzed in 2 different ways because the carpal motion was not
Figure 2. Fastrak motion-detecting sensors mounted directly to the third metacarpal and indirectly to the scaphoid and lunate (via nonmetallic posts). The Fastrak sensors are approximately 3 by 2.1 by 1.2 cm and weigh 8 g.
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The Journal of Hand Surgery / Vol. 29A No. 3 May 2004
linear. First, during half of each cycle of motion (ie, from extension to flexion) the angular travel, or excursion, of each carpal was expressed as a vector sum of its flexion/extension and radial/ulnar deviation during 10 increments of that half cycle of motion. For example, during the pure wrist flexion/extension motion (Fig. 1, motion A) the third metacarpal would have had a summed excursion of 60°. During the pure wrist radial/ulnar deviation motion (motion I) there would be an excursion of 30°. The excursions of the scaphoid and lunate then were computed as a percentage of the third metacarpal excursion. Second, the average orientation of each motion with respect to the sagittal (flexion/extension) plane (Fig. 1) was determined over 8 increments of each bone’s motion during one half of a cycle of wrist motion. These orientations then were averaged for the 7 specimens. For example, for a wrist pure flexion/extension motion the carpal would have an orientation angle of 0° if the carpal was moving in the same direction and in phase with the third metacarpal. For a pure wrist flexion/extension motion if the carpal was moving in the same plane as the third metacarpal
Table 1. Vector Excursion (Total Angular Travel in the Transverse Plane) of Scaphoid and Lunate as a Percentage of Third Metacarpal Motion Dart Throw Motion
Scaphoid (SD)
Lunate (SD)
A B C D E F G H I
88.6 (4.8) 74.6 (5.6) 61.1 (7.1) 48.2 (6.0) 34.2 (7.6) 25.6 (6.9) 27.2 (5.3) 45.8 (6.0) 74.3 (6.9)
53.0 (10.1) 40.2 (8.3) 31.1 (8.2) 23.1 (6.3) 22.1 (5.8) 25.6 (4.8) 37.5 (6.4) 55.6 (7.1) 76.1 (10.7)
but out of phase (ie, moving in the opposite direction) it would have an angle of 180°. Changes in scaphoid and lunate excursion and orientation with each type of dart throw motion were analyzed statistically by using a repeated-measures analysis of variance (Duncan, p ⬍ .05).
Results During pure wrist flexion and extension the scaphoid and lunate moved in nearly the same plane of motion as the wrist but with less excursion (Fig. 3; Tables 1, 2). As the wrist motion changed from pure flexion and extension to motions B and C, the scaphoid and lunate continued to have an orientation of motion similar to the wrist (Table 2). During the intermediate dart throw motions the scaphoid and lunate no longer had a relatively planar motion and had less excursion (Fig. 4). During motions F and G the
Table 2. Orientation (in °) of the Third Metacarpal, Scaphoid, and Lunate Motions With Respect to the Sagittal Plane
Figure 3. Scaphoid, lunate, and third metacarpal (wrist) motions during motion A. The scaphoid and lunate move together with the wrist, however, with less excursion.
Dart Throw Motion
Third Metacarpal
Scaphoid (SD)
Lunate (SD)
A B C D E F G H I
0.0 9.5 18.4 26.6 36.9 45 56.3 71.6 90.0
5.1 (3.6) 7.0 (3.9) 10.4 (2.8) 16.5 (4.5) 29.5 (8.6) 54.0 (19.4) 137.3 (27.5) 162.5 (10.7) 160.5 (4.8)
3.8 (4.4) 12.1 (8.3) 19.5 (11.7) 35.3 (15.3) 90.7 (48.0) 124.3 (35.9) 153.5 (13.4) 154.8 (5.0) 152.5 (15.0)
NOTE. The third metacarpal motions correspond to those in Figure 1 and are planar motions with increasing amounts of initial radial deviation. See Figure 1 for definition of orientation angle. The average and SDs are given for the 7 specimens.
Werner et al / Carpal Motion During a Dart Throw
Figure 4. Scaphoid, lunate, and third metacarpal (wrist) motions during motion F. During this dart throw motion the scaphoid and lunate have far less motion and do not have a planar pattern of travel.
scaphoid had its statistically smallest excursions. The lunate had its statistically smallest excursion during motions D, E, and F. During these intermediate dart throw motions the orientation of the scaphoid and lunate, relative to themselves, were statistically different from all other motions. As expected, when the wrist moved in pure radial and ulnar deviation the scaphoid and lunate mostly flexed and extended, respectively (Fig. 5). This phase shift in scaphoid motion occurred between motions F and G and in lunate motion between D and E, E and F, or F and G (Table 2).
421
during pure wrist flexion and extension. The results from the current study compare well (Table 3) with the results from Moojen et al,13 the results from other researchers as summarized by Moojen et al,13 and the results from one of our previous studies.10 Savelberg et al14 did examine carpal motions during wrist motions other than planar flexion/extension and planar radial/ulnar deviation; however, most of their data in a semispheric envelope of motion came from only one specimen. As presented, their data are difficult to compare with the findings of our study for specific planar ranges of dart throw motion. There are a number of limitations to this study. First, this study is based on the use of fresh cadaver material. Specimens with pre-existing ligament injuries were eliminated from the study, however, and data collection was completed within 1 day. Second, the applied tendon forces are an estimation of in vivo physiologic loads because the true loads in a living subject are not completely known. Even if the applied loads are only an approximation of in vivo loading, however, their use is better than no or minimal loads. Kobayashi et al15 have shown that joint loading in cadaver forearms has an important effect on carpal kinematics. Additionally, dynamic joint loading has been shown to affect the path of carpal motion, for example, carpal motion is different as the wrist moves from radial to ulnar deviation as compared with when the wrist moves from ulnar to radial deviation.16 A third limitation is that a restricted dart throw motion was analyzed. During pure wrist flexion/extension the total range of motion was only 60°.
Discussion These results show that the primary motion of the scaphoid and lunate is a flexion/extension motion regardless of the type of wrist motion. During pure wrist flexion and extension the scaphoid and lunate follow the wrist motion. During wrist radial and ulnar deviation the scaphoid and lunate still flex and extend. During certain intermediate dart throw motions the scaphoid moves as little as 26% of the wrist motion and the lunate as little as 22% of the wrist motion. Most results from other researchers are reported as the contribution of a carpal motion in the plane of flexion/extension or the plane of radial/ulnar deviation. To compare a subset of our results with others, we computed the percent contribution of the scaphoid and lunate in the plane of wrist flexion/extension
Figure 5. Scaphoid, lunate, and third metacarpal (wrist) motions during motion I. In this motion the scaphoid and lunate are moving in primarily a flexion/extension direction while the wrist is deviating radially and ulnarly.
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Table 3. Sagittal Plane Motion of Scaphoid and Lunate During Pure Wrist Flexion and Extension (Percentage of Wrist Motion)
Scaphoid Lunate
Data From Moojen et al13
Data (Average) From Review of Other Researchers, Moojen et al13
Data From Previous Study10
Data From Current Study
75 49
78 49
92 45
88 52
The findings from this study suggest that clinically each subject might have a dart throw motion (eg, motion E or F) that has minimal scaphoid and lunate motion. If a subject’s wrist motion could be restrained clinically to this dart throw motion, in orientation and magnitude, early hand motion might be possible after those surgeries in which minimal scaphoid and lunate motion might be desired (eg, carpal arthrodeses, ligamentous repairs, and comminuted distal radius fractures).
8.
9.
10.
References 1. Palmer AK, Werner FW, Murphy D, Glisson R. Functional wrist motion: a biomechanical study. J Hand Surg 1985; 10A:39 – 46. 2. Berger RA, Crowninshield RD, Flatt AE. The three-dimensional rotational behaviors of the carpal bones. Clin Orthop 1982;167:303–310. 3. Ruby LK, Cooney WP III, An KN, Linscheid RL, Chao EYS. Relative motion of selected carpal bones: a kinematic analysis of the normal wrist. J Hand Surg 1988;13A:1–10. 4. Patterson RM, Nicodemus CL, Viegas SF, Elder KW, Rosenblatt J. High-speed, three-dimensional kinematic analysis of the normal wrist. J Hand Surg 1998;23A:446 – 453. 5. Wolfe SW, Neu C, Crisco JJ. In vivo scaphoid, lunate, and capitate kinematics in flexion and in extension. J Hand Surg 2000;25A:860 – 869. 6. Kobayashi M, Berger RA, Nagy L, Linscheid RL, Uchiyama S, Ritt M, et al. Normal kinematics of carpal bones: a three-dimensional analysis of carpal bone motion relative to the radius. J Biomech 1997;30:787–793. 7. Moojen TM, Snel JG, Ritt MJPF, Kauer JMG, Venema HW,
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16.
Bos KE. Three-dimensional carpal kinematics in vivo. Clin Biomech 2002;17:506 –514. Crisco JJ, Wolfe SW, Neu CP, Pike S. Advances in the in vivo measurement of carpal kinematics. Orthop Clin North Am 2001;32:219 –231. Short WH, Werner FW, Green JK, Weiner MM, Masaoka S. The effect of sectioning the dorsal radiocarpal ligament and insertion of a pressure sensor into the radiocarpal joint on scaphoid and lunate kinematics. J Hand Surg 2002;27A:68 – 76. Werner FW, Short WH, Fortino MD, Palmer AK. The relative contribution of selected carpal bones to global wrist motion during simulated planar and out-of-plane wrist motion. J Hand Surg 1997;22A:708 –713. Short WH, Werner FW, Green JK, Masaoka S. Biomechanical evaluation of ligamentous stabilizers of the scaphoid and lunate. J Hand Surg 2002;27A:991–1002. Werner FW, Palmer AK, Somerset JH, Tong JJ, Gillison DB, Fortino MD, et al. Wrist joint motion simulator. J Orthop Res 1996;14:639 – 646. Moojen TM, Snel JG, Ritt MJPF, Venema HW, Kauer JMG, Bos KE. In vivo analysis of carpal kinematics and comparative review of the literature. J Hand Surg 2003;28A:81– 87. Savelberg HHCM, Otten JDM, Kooloos JGM, Huiskes R, Kauer JMG. Carpal bone kinematics and ligament lengthening studied for the full range of joint movement. J Biomech 1993;26:1389 –1402. Kobayashi M, Garcia-Elias M, Nagy L, Ritt MJPF, An K-N, Cooney WP, et al. Axial loading induces rotation of the proximal carpal row bones around unique screw-displacement axes. J Biomech 1997;30:1165–1167. Short WH, Werner FW, Fortino MD, Mann KA. Analysis of the kinematics of the scaphoid and lunate in the intact wrist joint. Hand Clin 1997;13:93–108.
Purpose: The primary purpose of this study was to measure the in vitro scaphoid and lunate motion during 9 different variations of a wrist dart throw motion. Another goal was to determine the specific dart throw motion that minimized scaphoid and lunate motion. Methods: Scaphoid and lunate motion were recorded in 7 cadaver forearms during various combinations of wrist dart throw motions caused by a wrist joint motion simulator. Results: During wrist flexion and extension the scaphoid and lunate motions follow the wrist motion. During wrist radial and ulnar deviation the scaphoid and lunate correspondingly flex and extend. During intermediate motions the scaphoid and lunate move as little as 26% of the total third metacarpal motion and do not necessarily follow a planar motion. Conclusions: These findings suggest that there may be a dart throw motion during which there may be minimal scaphoid and lunate motion. If a subject’s wrist motion could be clinically restricted to this dart throw motion, early hand mobility might be possible after surgery on the scaphoid and lunate. (J Hand Surg 2004;29A:418 – 422. Copyright © 2004 by the American Society for Surgery of the Hand.) Key words: Carpal motion, wrist dart throw.
Many activities of daily living require a motion that is a combination of wrist flexion/extension and radial/ulnar deviation.1 This is referred to as a wrist
From the Department of Orthopedic Surgery, Institute for Human Performance, State University of New York Upstate Medical University, Syracuse, NY. Received for publication July 23, 2003; accepted in revised form January 27, 2004. Supported by extramural research from the National Center for Injury Prevention and Control grant number R49/CCR216814-03 from the Centers for Disease Control and Prevention, and by the National Institutes for Health grant 1R01 AR50099-01. 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. The contents of this article are solely the responsibility of the authors and do not necessarily represent the official views of the Center for Disease Control and Prevention or the National Institutes of Health. Reprint requests: Frederick W. Werner, MME, Department of Orthopedic Surgery, Institute for Human Performance, SUNY Upstate Medical University, 750 E. Adams St, Syracuse, NY 13210. Copyright © 2004 by the American Society for Surgery of the Hand 0363-5023/04/29A03-0013$30.00/0 doi:10.1016/j.jhsa.2004.01.018
418
The Journal of Hand Surgery
dart throw motion. The act of throwing a dart requires an arc of motion starting in wrist extension and radial deviation moving to wrist flexion and ulnar deviation. This requires moving the wrist in a complex 2-dimensional motion. The majority of in vivo and in vitro kinematic data for the wrist carpals have been measured during pure or quasipure wrist flexion/extension or wrist radial/ulnar deviation.2–9 In one study10 scaphoid and lunate motion were measured for one dart throw motion from 20° of extension and 10° of radial deviation to 20° of flexion and 10° of ulnar deviation. It has been suggested (Marc Garcia-Elias, personal communication, June 2001) that there may be a specific wrist dart throw motion during which there is minimal scaphoid or lunate motion. This study measured the in vitro scaphoid and lunate motion during 9 different variations of a wrist dart throw motion. The purpose of this study was to determine the specific dart throw plane of motion that minimized scaphoid and lunate motion.
Werner et al / Carpal Motion During a Dart Throw
Figure 1. Nine dart throw wrist motions studied as viewed in the transverse plane. Motion A is a pure extension to flexion motion. Motion I is a pure radial deviation to ulnar deviation. The other 7 motions were as the wrist moved from extension and radial deviation to flexion and ulnar deviation. The length of each line corresponds to the excursion of the motion.
Materials and Methods Seven fresh normal cadaver forearms were prepared for use in a wrist joint servohydraulic motion simulator in a manner similar to that used in previously published studies.9,11 The average age of the specimens was 66 years. There was 1 male and 6 female specimens. There were 4 specimens with a type 1 lunate and 3 specimens with a type 2 lunate. Each forearm was determined by fluoroscopy and arthroscopic examination to be free of traumatic and systemic defects. The major wrist tendons (extensor carpi ulnaris, extensor carpi radialis brevis, extensor carpi radialis longus, abductor pollicis longus, flexor carpi radialis, and flexor carpi ulnaris) were kept intact for the attachment of the corresponding hydraulic actuators in the wrist simulator.12 All capsular and retinacular structures were spared. Physiologic tendon loading was used to cause 9 variations of wrist motion (Fig. 1). The motions ranged from a cyclic flexion/extension motion (30° extension to 30° flexion, with 0° of radial/ulnar deviation; Fig. 1, motion A), to 7 dart throw motions in which the wrist moved from wrist extension and radial deviation to flexion and ulnar deviation (motions B, C, D, E, F, G, H), and finally to a pure radial/ulnar deviation motion (10° radial deviation to 20° ulnar deviation, with 0° of flexion/extension; motion I).
419
Sensors (Fastrak; Polhemus, Colchester, VT) (Fig. 2) were attached11 indirectly to the scaphoid and lunate, and directly to the third metacarpal whose motion was defined to be equivalent to wrist motion (based on the International Society for Biomechanics proposed standard definition for the wrist and hand joint coordinate systems; http://www.isbweb.org/ standards/wrist.html). The sensors for the scaphoid and lunate were mounted onto acrylic platforms that were glued onto pultruded carbon fiber rods. The rods were inserted and cemented into 2.7-mm unicortical drill holes in each bone. During each cyclic motion these sensors measured the 3-dimensional motion of these bones relative to electromagnetic sources mounted onto the ulna, with an accuracy of 0.2° and 0.2 mm.9 An agonist-antagonist muscle tendon load algorithm was used to control wrist motion based on the third metacarpal motion data. This algorithm has been shown to maintain an actual wrist flexion/extension motion to within 1° of a pure planar motion (ie, there was less than 1° change from neutral radial/ulnar deviation during a pure flexion/ extension motion).9 This method permitted fine control of wrist motion and allowed clear differentiation between different dart throw motions that could not be possible in vivo without exterior guidance to the wrist. Scaphoid and lunate motion were analyzed in 2 different ways because the carpal motion was not
Figure 2. Fastrak motion-detecting sensors mounted directly to the third metacarpal and indirectly to the scaphoid and lunate (via nonmetallic posts). The Fastrak sensors are approximately 3 by 2.1 by 1.2 cm and weigh 8 g.
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The Journal of Hand Surgery / Vol. 29A No. 3 May 2004
linear. First, during half of each cycle of motion (ie, from extension to flexion) the angular travel, or excursion, of each carpal was expressed as a vector sum of its flexion/extension and radial/ulnar deviation during 10 increments of that half cycle of motion. For example, during the pure wrist flexion/extension motion (Fig. 1, motion A) the third metacarpal would have had a summed excursion of 60°. During the pure wrist radial/ulnar deviation motion (motion I) there would be an excursion of 30°. The excursions of the scaphoid and lunate then were computed as a percentage of the third metacarpal excursion. Second, the average orientation of each motion with respect to the sagittal (flexion/extension) plane (Fig. 1) was determined over 8 increments of each bone’s motion during one half of a cycle of wrist motion. These orientations then were averaged for the 7 specimens. For example, for a wrist pure flexion/extension motion the carpal would have an orientation angle of 0° if the carpal was moving in the same direction and in phase with the third metacarpal. For a pure wrist flexion/extension motion if the carpal was moving in the same plane as the third metacarpal
Table 1. Vector Excursion (Total Angular Travel in the Transverse Plane) of Scaphoid and Lunate as a Percentage of Third Metacarpal Motion Dart Throw Motion
Scaphoid (SD)
Lunate (SD)
A B C D E F G H I
88.6 (4.8) 74.6 (5.6) 61.1 (7.1) 48.2 (6.0) 34.2 (7.6) 25.6 (6.9) 27.2 (5.3) 45.8 (6.0) 74.3 (6.9)
53.0 (10.1) 40.2 (8.3) 31.1 (8.2) 23.1 (6.3) 22.1 (5.8) 25.6 (4.8) 37.5 (6.4) 55.6 (7.1) 76.1 (10.7)
but out of phase (ie, moving in the opposite direction) it would have an angle of 180°. Changes in scaphoid and lunate excursion and orientation with each type of dart throw motion were analyzed statistically by using a repeated-measures analysis of variance (Duncan, p ⬍ .05).
Results During pure wrist flexion and extension the scaphoid and lunate moved in nearly the same plane of motion as the wrist but with less excursion (Fig. 3; Tables 1, 2). As the wrist motion changed from pure flexion and extension to motions B and C, the scaphoid and lunate continued to have an orientation of motion similar to the wrist (Table 2). During the intermediate dart throw motions the scaphoid and lunate no longer had a relatively planar motion and had less excursion (Fig. 4). During motions F and G the
Table 2. Orientation (in °) of the Third Metacarpal, Scaphoid, and Lunate Motions With Respect to the Sagittal Plane
Figure 3. Scaphoid, lunate, and third metacarpal (wrist) motions during motion A. The scaphoid and lunate move together with the wrist, however, with less excursion.
Dart Throw Motion
Third Metacarpal
Scaphoid (SD)
Lunate (SD)
A B C D E F G H I
0.0 9.5 18.4 26.6 36.9 45 56.3 71.6 90.0
5.1 (3.6) 7.0 (3.9) 10.4 (2.8) 16.5 (4.5) 29.5 (8.6) 54.0 (19.4) 137.3 (27.5) 162.5 (10.7) 160.5 (4.8)
3.8 (4.4) 12.1 (8.3) 19.5 (11.7) 35.3 (15.3) 90.7 (48.0) 124.3 (35.9) 153.5 (13.4) 154.8 (5.0) 152.5 (15.0)
NOTE. The third metacarpal motions correspond to those in Figure 1 and are planar motions with increasing amounts of initial radial deviation. See Figure 1 for definition of orientation angle. The average and SDs are given for the 7 specimens.
Werner et al / Carpal Motion During a Dart Throw
Figure 4. Scaphoid, lunate, and third metacarpal (wrist) motions during motion F. During this dart throw motion the scaphoid and lunate have far less motion and do not have a planar pattern of travel.
scaphoid had its statistically smallest excursions. The lunate had its statistically smallest excursion during motions D, E, and F. During these intermediate dart throw motions the orientation of the scaphoid and lunate, relative to themselves, were statistically different from all other motions. As expected, when the wrist moved in pure radial and ulnar deviation the scaphoid and lunate mostly flexed and extended, respectively (Fig. 5). This phase shift in scaphoid motion occurred between motions F and G and in lunate motion between D and E, E and F, or F and G (Table 2).
421
during pure wrist flexion and extension. The results from the current study compare well (Table 3) with the results from Moojen et al,13 the results from other researchers as summarized by Moojen et al,13 and the results from one of our previous studies.10 Savelberg et al14 did examine carpal motions during wrist motions other than planar flexion/extension and planar radial/ulnar deviation; however, most of their data in a semispheric envelope of motion came from only one specimen. As presented, their data are difficult to compare with the findings of our study for specific planar ranges of dart throw motion. There are a number of limitations to this study. First, this study is based on the use of fresh cadaver material. Specimens with pre-existing ligament injuries were eliminated from the study, however, and data collection was completed within 1 day. Second, the applied tendon forces are an estimation of in vivo physiologic loads because the true loads in a living subject are not completely known. Even if the applied loads are only an approximation of in vivo loading, however, their use is better than no or minimal loads. Kobayashi et al15 have shown that joint loading in cadaver forearms has an important effect on carpal kinematics. Additionally, dynamic joint loading has been shown to affect the path of carpal motion, for example, carpal motion is different as the wrist moves from radial to ulnar deviation as compared with when the wrist moves from ulnar to radial deviation.16 A third limitation is that a restricted dart throw motion was analyzed. During pure wrist flexion/extension the total range of motion was only 60°.
Discussion These results show that the primary motion of the scaphoid and lunate is a flexion/extension motion regardless of the type of wrist motion. During pure wrist flexion and extension the scaphoid and lunate follow the wrist motion. During wrist radial and ulnar deviation the scaphoid and lunate still flex and extend. During certain intermediate dart throw motions the scaphoid moves as little as 26% of the wrist motion and the lunate as little as 22% of the wrist motion. Most results from other researchers are reported as the contribution of a carpal motion in the plane of flexion/extension or the plane of radial/ulnar deviation. To compare a subset of our results with others, we computed the percent contribution of the scaphoid and lunate in the plane of wrist flexion/extension
Figure 5. Scaphoid, lunate, and third metacarpal (wrist) motions during motion I. In this motion the scaphoid and lunate are moving in primarily a flexion/extension direction while the wrist is deviating radially and ulnarly.
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Table 3. Sagittal Plane Motion of Scaphoid and Lunate During Pure Wrist Flexion and Extension (Percentage of Wrist Motion)
Scaphoid Lunate
Data From Moojen et al13
Data (Average) From Review of Other Researchers, Moojen et al13
Data From Previous Study10
Data From Current Study
75 49
78 49
92 45
88 52
The findings from this study suggest that clinically each subject might have a dart throw motion (eg, motion E or F) that has minimal scaphoid and lunate motion. If a subject’s wrist motion could be restrained clinically to this dart throw motion, in orientation and magnitude, early hand motion might be possible after those surgeries in which minimal scaphoid and lunate motion might be desired (eg, carpal arthrodeses, ligamentous repairs, and comminuted distal radius fractures).
8.
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