LIRN Assignment

From the *Department of Orthopedic Surgery, Osaka University Medicine, Suita, Osaka, Japan.

Received for publication October 17, 2016; accepted in revised form

This work was supported by Japan Society for the Promotion of Sc Number JP15K10442.

Corresponding author: Kunihiro Oka, MD, PhD, Department of Osaka University Graduate School of Medicine, 2-2, Yamada-oka, Su Japan; e-mail: [email protected].

0363-5023/18/4302-0012$36.00/0 http://dx.doi.org/10.1016/j.jhsa.2017.07.028

182.e1 r � 2018 ASSH r Published by Elsevier, I

SCIENTIFIC ARTICLE

In Vivo 3-Dimensional Kinematics of Thumb

Carpometacarpal Joint During Thumb Opposition

Yohei Kawanishi, MD, PhD,* Kunihiro Oka, MD, PhD,* Hiroyuki Tanaka, MD, PhD,* Kiyoshi Okada, MD, PhD,* Kazuomi Sugamoto, MD, PhD,* Tsuyoshi Murase, MD, PhD*

Purpose This study primarily aimed to demonstrate the screw-home rotation of the thumb car- pometacarpal (CMC) joint and the function of surrounding ligaments during thumb oppositional motion.

Methods A 3-dimensional kinematic analysis of the thumb CMC joint was conducted using data derived from computed tomography of 9 healthy volunteers. Scans were obtained in the neutral forearmandwrist position and the thumb inmaximumradial abduction,maximumpalmar abduction, andmaximumopposition. Themovements of thefirstmetacarpal and the palmar and dorsal bases on the trapezium during thumb oppositional motion from radial abduction through palmar abduction were quantified using a coordinate system originating on the trapezium. In addition to the kinematic analyses, the length of virtual ligaments, including the anterior oblique, ulnar collateral, dorsal radial, dorsal central (DCL), and posterior oblique ligament (POL), were calculated at each thumb position.

Results From radial abduction to opposition of the thumb through palmar abduction, the first metacarpal was abducted, internally rotated, and flexed on the trapezium. The palmar base of the first metacarpal moved in the palmar-ulnar direction, and the dorsal base moved in the palmar-distal direction along the concave surface of the trapezium. Although the DCL and POL lengthened, the lengths of other ligaments did not change significantly.

Conclusions During thumb oppositionalmotion, internal rotation of the first metacarpal occurred, with the palmar base rotating primarilywith respect to the dorsal base. TheDCLandPOLmaybe strained in thumb functional positions.

Clinical relevance Kinematic variables indicated a screw-home rotation of the thumb CMC joint and the contribution of the dorsal ligaments to the stability of the rotation on the pivot point. (J Hand Surg Am. 2018;43(2):182.e1-e7. Copyright � 2018 by the American Society for Surgery of the Hand. All rights reserved.) Key words Dorsal ligaments, kinematics, osteoarthritis, 3-dimensional, thumb carpometacarpal joint.

Graduate School of

July 26, 2017.

ience KAKENHI Grant

Orthopedic Surgery, ita, Osaka 565-0871,

nc. All rights reserved

T HE THUMB CARPOMETACARPAL (CMC) joint is a saddle-shaped and semiconstrained joint with a wide range of motion. Thumb mobility thus

allows the performance of unique functions such as pinching and grasping in tandem with other fingers. During these movements, the thumb CMC joint is proposed to be stabilized by a screw-home rotation that allows the palmar beak of the first metacarpal to lock into the palmar recess of the trapezium.1 The anterior oblique ligament (AOL), 1 of the palmar

.

3-DIMENSIONAL KINEMATICS OF THUMB CMC JOINT 182.e2

ligaments of the thumb CMC joint, has been regarded as the primary stabilizer of the joint,2 but recent studies indicate that the AOL plays a secondary sta- bilization role compared with the dorsal ligament complex. An anatomical study showed a lack of deep fibers of the AOL in 27 of 30 normal cadaveric hands (90%), and tissues of the dorsal ligaments appeared more organized, with greater cellularity and more sensory innervation than the AOL.3 Several biome- chanical studies have found that the dorsal ligaments are stronger than the AOL.4e6 Taut dorsal ligaments are proposed to function as stabilizers during screw- home rotation and enable the palmar beak of the first metacarpal to cantilever into the palmar recess of the trapezium.1

The dorsal radial ligament (DRL) has been consid- ered to be the strongest of the dorsal ligaments4 and more important as a stabilizer6,7 of the thumb CMC joint than the posterior oblique ligament (POL). How- ever, the dorsal central ligament (DCL), which is the thickest and shortest component of the dorsal ligament complex,3 may also be a stabilizer. The contributions of the DRL and DCL are unclear because previous studies have not assessed these 2 ligaments separately.4e9

Evaluation of joint motion in 2 axes is difficult with conventional 2-dimensional techniques,10e13 but a markerless 3-dimensional analytical technique is available for in vivo kinematic analysis of the thumb CMC joint.14e17 Crisco et al14 described the orien- tation of the functional axes of the thumb CMC joint as a potentially stabilizing screw-home rotation. Computed recruitment patterns of the AOL and DRL indicated the importance of the DRL.8

We evaluated 3-dimensional thumb CMC joint kinematics and virtual ligament length surrounding the joint during thumb opposition, focusing on the motion of the first metacarpal base because articular interactions reflect the details of screw-home rotation and the mechanical effects on the surrounding liga- ments. The study objective was to use in vivo kine- matics data to describe the screw-home motion of the thumb CMC joint during thumb oppositional motion and the function of each of the 3 dorsal ligaments.

METHODS Nine male Japanese volunteers (mean age, 34.3 years; range 32e42 years) with no history of trauma or disease of the right upper extremity were included in the analysis. The study protocol was approved by the local institutional review board. The kinematics of the thumb CMC joint during thumb motion included first metacarpal movement on the trapezium and focused

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on the palmar and dorsal bases of the first metacarpal bone. Movements were assessed 3-dimensionally and quantified using a coordinate system originating on the trapezium.

The right wrist was immobilized using a short-arm thumb spica cast with the thumb in a position of maximal palmar abduction in a plane perpendicular to the palm and the wrist aligned in a neutral position. A roll of 3-inch padding and 3-inch fiberglass cast ma- terial (3M Company, Oakdale, MN) was used for each wrist. Hands were scanned by low-radiation computed tomography (CT) (scan time, 0.5 s; slice thickness, 1.25mm; 10mA; 120 kV) using a LightSpeedUltra 16 CT system (General Electric, Waukesha, WI) pro- ducing one-thirtieth of the normal radiation dose.18

The subjects were in the prone position on the CT ta- ble with their arms elevated over the head, the elbows flexed at 90�, and the forearm in a neutral position during the scan. After a CT scan with the maximum palmar thumb abduction, the thumb portion of the thumb spica cast was removed to allow the thumb to abduct radially and oppose to the proximal palmar crease of the little finger, which was defined as maximum opposition. Each subject underwent a CT scan with the thumb in 2 additional positions: maximum radial abduction in the plane of the palm and maximum opposition. Data were saved in the Digital Imaging and Communications in Medicine format and stored in a computer (Dell Precision M4600, 2.50 GHz/4G; Dell, Inc., Round Rock, TX). Contours of the radius, ulna, carpal bones, and first metacarpal 3-dimensional surface generation of the bone cortex19

were created using commercial software (BV; Orthree Co., Ltd., Osaka, Japan). The digital models were visualized using software (BS; Orthree Co., Ltd.) that enabled digital 3-dimensional measurements on the computer.

Thumb CMC joint kinematics

Kinematic variables of the thumb CMC joint were calculated by registering the bone in various positions, which were then compared relative to an orthogonal coordinate system originating on the trapezium (Fig. 1A) as previously reported.20e22 The z axis, whichwas nearly parallel to the central ridge, indicated the radial (þ)/ulnar (�) direction and passed through the top of the radial facet and the top of the ulnar facet. The x axis, indicating the palmar (þ)/dorsal (�) direction, ran perpendicular to the z axis and passed through the midpoint of the dorsal surface. The y axis, indicating the proximal (þ)/distal (�) direction, was perpendicular to the x and z axes. Rotation around the x axis indicated ulnar (þ)/radial (�) deviation,

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FIGURE 1: Orthogonal reference system including the trapezium.AAblue broken line is the central ridge of the trapezial articular surface. B The palmar and dorsal cusps (green circles) of the proximal articular surface of the first metacarpal in lateral and proximal views.

182.e3 3-DIMENSIONAL KINEMATICS OF THUMB CMC JOINT

rotation around the y axis indicated internal rotation (þ)/external rotation (�), and rotation around the z axis indicated flexion (þ)/extension (�). The posi- tional changes in the first metacarpal relative to the trapezium were calculated using Euler angles, which quantify spatial joint motion using 3 sequential rota- tions for interpreting motion in coordinate systems.17

The palmar and dorsal cusps of the proximal base of the first metacarpal were assigned point values (Fig. 1B), and the positions of these points in the trapezium coordinate system were also calculated at each position during thumb motion. The thumb CMC joint motions were analyzed in the following order: maximum radial position, palmar, and oppositional position using the static CT data in these 3 positions.

Ligament length

Two palmar ligaments, the AOL and the ulnar collat- eral ligament (UCL), and 3 dorsal ligaments, the DRL, DCL, and POL, were studied. The origins and insertions of these ligamentsweremanuallymarked on the bone models as described by Ladd et al3 (Fig. 2). The AOL attaches proximally on the palmar crest of the trapezium and distally on the palmar beak of the first metacarpal. The UCL attaches proximally on the ulnar-palmar ridge of the trapezium and distally on the palmar-ulnar edge of the first metacarpal base. The DRL, DCL, and POL attach proximally on the radial, center, and ulnar aspects of the dorsal tubercle of

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the trapezium and distally on the radial side, center, and ulnar side of the dorsal aspect of the first meta- carpal base, respectively. Avoiding bone penetration in 3-dimensional space, all ligament paths were modeled, and the length at each positionwas computed as the shortest distance between the origin and the insertion.8,23 Because this method could not account for the effects of ligament tension, significant changes in static length were defined as taut or loosened ligaments.

Data analysis

Differences in measurements at opposition or palmar abduction and at radial abduction were compared, and ligament lengthening or shortening was expressed as percentages. Data were expressed as means and stan- dard error; 1-way analysis of variance was performed to determine significant differences. A P value of less than .05 was considered statistically significant.

RESULTS Thumb CMC joint kinematics

During thumb movement from radial abduction to opposition through palmar abduction, the first metacarpal was abducted, internally rotated, andflexed significantly on the trapezium (Fig. 3). During movement from radial to palmar abduction, the first metacarpal abducted 25.8� � 6.6� (P< .05), internally

l. 43, February 2018

FIGURE 2: A Palmar ligament models show the AOL (red) and UCL (orange). B Dorsal ligament models show the DRL (blue), DCL (turquoise), and POL (light turquoise). C The estimated length values during thumb motion.

FIGURE 3: Motion of the first metacarpal during thumb opposition. The first metacarpal A abducted, B internally rotated, and C flexed on the trapezium. Curved red arrows show the motion from radial abduction (blue bone) to palmar abduction (yellow bone), and the curved blue arrows show the motion from palmar abduction to opposition (pink bone).

3-DIMENSIONAL KINEMATICS OF THUMB CMC JOINT 182.e4

rotated 16.8� � 4.0� (P< .05), and flexed 20.6� � 4.5�

(P < .05). During movement from radial abduction to opposition, the first metacarpal abducted 26.6� � 6.6�

(P < .05), internally rotated 22.3� � 4.0� (P < .05), and flexed 25.0� � 4.5� (P < .05).

During the sequence of thumb oppositional mo- tion, the first metacarpal flexes and pronates with the dorsal base as the center. The palmar side moved significantly in the palmar-ulnar direction and the dorsal side moved significantly in the palmar-distal direction during movement from radial abduction to opposition (Fig. 4A and B). From radial abduction to opposition, the palmar cusp of the proximal articular surface of the first metacarpal translated 2.5 � 0.7 mm in the palmar direction (P < .05), 1.3 � 0.6 mm in the proximal direction (P ¼ .09), and 5.7 � 1.0 mm in the ulnar direction (P < .05). The dorsal

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cusp translated 3.1 � 0.8 mm in the palmar direction (P < .05), 3.9 � 0.8 mm in the distal direction (P < .05), and 0.5 � 0.7 mm in the ulnar direction (P ¼ .7). From radial to palmar abduction, the palmar cusp translated 2.3 � 0.7 mm in the palmar direction (P < .05), 0.8 � 0.6 mm in the proximal direction (P ¼ .4), and 5.0 � 1.0 mm in the ulnar direction (P < .05). The dorsal cusp translated 2.4� 0.8 mm in the palmar direction (P < .05), 3.5 � 0.8 mm in the distal direction (P < .05), and 1.2 � 0.7 mm in the ulnar direction (P ¼ .2).

Ligament length

Compared with the ligament length in radial abduc- tion, the palmar ligaments shortened, while the dorsal ligaments lengthened, in palmar abduction and op- position (Fig. 2C). Although the length changes in the

l. 43, February 2018

FIGURE 4: Movement locus of the palmar and dorsal cusps of the proximal articular surface of the first metacarpal on the articular surface of trapezium (green model) in A distal and B lateral views; blue, yellow, and red points indicate the cusps in radial abduction, palmar abduction, and opposition, respectively. The dorsal cusp moves in the distal-palmar direction and the palmar cusp moves in the palmar-ulnar direction in the palmar recess of thumb CMC joint during thumb oppositional motion from radial abduction. C These results mean that, during thumb oppositional motion, the first metacarpal flexes and rotates internally with the dorsal base as the center.

182.e5 3-DIMENSIONAL KINEMATICS OF THUMB CMC JOINT

DCL and POL were significant, the palmar ligaments and the DRL did not show any significant change in length. The DCL lengthened 2.3� 0.5 mm (41.6%; P < .05) and 2.1 � 0.5 mm (38.8%; P < .05), and the POL lengthened 4.0 � 0.8 mm (47.9%; P < .05) and 3.8 � 0.8 mm (46.6%; P < .05) from radial to palmar abduction and to opposition, respectively. The AOL shortened 1.2� 0.6 mm (20.3%; P¼ .2) and 0.9� 0.6 mm (15.6%; P ¼ .4), the UCL shortened 0.6 � 0.5 mm (10%; P¼ .5) and 0.9� 0.5 mm (14.4%; P¼ .2), and the DRL lengthened 0.4� 0.5 mm (5.6%; P¼ .7) and 0.8 � 0.5 mm (12.8%; P ¼ .3) from radial to palmar abduction and to opposition, respectively.

DISCUSSION Screw-home rotation in the thumb CMC joint is pro- posed to stabilize the thumb during movement. Taut dorsal ligaments of the thumb CMC joint enable rotation by a cantilever mechanism during thumb functional movement.1 Although previous biome- chanical studies have confirmed the importance of the dorsal ligaments as stabilizers of the thumb CMC,4e7

the 3 dorsal ligaments have not been evaluated sepa- rately. We analyzed in vivo 3-dimensional kinematics of the thumb CMC joint and changes in length of 2 virtual palmar and 3 dorsal ligaments during thumb opposition, while paying close attention to the motion of the first metacarpal base. The aim was to obtain kinematic evidence of screw-home rotation and the involvement of the 3 dorsal ligaments.

The study limitations include the sample size and character of the objectives. Although a larger number

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of participants may have resulted in different findings, our analysis had adequate power of greater than 0.9 in a post hoc power analysis (a ¼ 0.05). As all subjects in this studywere Japanesemen aged 30 to 49 years, there was no diversity of race, sex, and age. Consequently, racial-, sex-, and age-related differences in thumb CMC joint kinematics could not be clarified in this study. Third, the angle of thefirst metacarpal relative to the trapezium in each thumb position was not neces- sarily absolutely the same in all participants as shown in the standard error of the measurements. This variability might have been affected by individual differences in in vivo joint congruence24 and joint laxity.21 Fourth, the study did not consider the influ- ence of different fibers of each ligament because they were calculated as a line between their anatomical origin and did not have a width. Finally, we assessed the thumb CMC joint only at maximum radial abduc- tion, maximum palmar abduction, and maximum thumb opposition. However, the thumb can move intricately over a range of circumduction during these functions. Therefore, there exists a possibility that the thumb CMC joint has kinematics that were not apparent in this analysis.

Although the first metacarpal internally rotated on the trapezium during opposition from radial abduction (Fig. 3B), the motion of the first metacarpal indicated that the palmar base rotated primarily with respect to the dorsal base in the palmar recess of thumb CMC joint (Fig. 4C). Edmunds1 hypothesized a screw-home rotation of the thumb CMC joint in which the palmar base of the first metacarpal rotates in the palmar recess of the joint. Recent kinematic studies found that the

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3-DIMENSIONAL KINEMATICS OF THUMB CMC JOINT 182.e6

rotation is coupled with thumb flexion-extension and abduction-adduction, and that internal rotation of the first metacarpal is coupled with thumb flexion or abduction.14,15 Kinematic variables in our study visualized the screw-home rotation and supported the results of previous studies because the first metacarpal in our series also abducted and flexed on the trapezium along with internal rotation (Fig. 3A, C).

Stable screw-home motion of the thumb CMC joint can be facilitated by taut dorsal ligaments working as a joint stabilizer during thumb oppositional motion.6

In this study, during thumb opposition from radial abduction, the dorsal ligaments, except for the DRL, lengthened, but the lengths of the 2 palmar ligaments did not change significantly. If these dorsal ligaments are presumed to remain taut as they lengthen, they can be seen as contributing to a stable screw-home rota- tion. Halilaj et al8 reported high in vivo recruitment of the DRL, separated into radial, central, and ulnar fibers that could be regarded as a taut ligament, with radial fibers stabilizing adduction and the ulnar fiber stabilizing both adduction and flexion. These radial and ulnar fibers can be considered as the DRL and DCL in our study, respectively, because the path of each fiber in their study was nearly the same as that of the ligaments in our study. Their ulnar fiber was the shortest dorsal ligament, which is characteristic of the DCL. Therefore, the DRL might not significantly lengthen for abduction, and the DCL might signifi- cantly lengthen for flexion of the thumb CMC joint. The POL lengthened significantly during thumb opposition from radial abduction, as previously reported.9 The contribution of the POL as a stabilizer of the thumb CMC joint may be smaller than that of the DRL and DCL.6 However, the POL may contribute to a stable screw-home rotation in combi- nation with a taut DCL that increases in length during thumb movement. To demonstrate additional details of the changes in the ligaments surrounding the thumb CMC joint during thumb motion, cadaver studies to measure the tension of each ligament are necessary. Because the location of these ligaments, especially palmar ones, is variable, the information that can be gained from the estimated length changes of virtual ligaments in this and previous studies are limited.

The thumb CMC joint is commonly affected by osteoarthritis, with the palmar portion being most often involved.24e27 Although thumb CMC joint osteoarthritis may be associated with AOL degener- ation,27 palmar cartilage wear in the thumb CMC joint can develop without AOL degeneration.28 Our study revealed rotational motion of the first meta- carpal on the trapezium with the dorsal side as a

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pivot. The cartilage on the palmar-ulnar portion of the thumb CMC joint is the active contact area during thumb function and is thinner than the cartilage in other areas of the joint.29 The predominant rotation of the palmar side of the first metacarpal base may be an additional, direct cause of damage of the articular cartilage and contribute to the development of thumb CMC joint osteoarthritis. However, additional kine- matic study comparing arthritic and normal hands is needed to confirm our hypothesis of the pathogenesis of thumb CMC joint osteoarthritis.

This study analyzed the in vivo 3-dimensional kinematics of the thumb CMC joint and the length changes in the surrounding ligaments during thumb opposition. The rotational motion of the first meta- carpal base on the trapezium predominantly occurred on the palmar side with the dorsal side as a pivot, indicating screw-home rotation with the possible effect of the DCL and POL on stability during thumb oppositional motion.

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