The Role of Scapholunate Interosseous, Dorsal Intercarpal, and Radiolunate Ligaments in Wrist Biomechanics

Abstract

Rupture to wrist ligaments predisposes the joint to degenerative changes. Scapholunate interosseous ligament (SLIL) rupture, especially when compounded by dorsal intercarpal ligament (DIC) and long radiolunate ligament (LRL) disruption, can cause carpal bone kinematic abnormalities. It is essential to delineate the role of these ligaments and their constraints on wrist range-of-motion (ROM) and center of rotation (COR). Wrist ROM and COR location were determined in 9 specimens using a six degree-of-freedom robotic musculoskeletal simulator in 24 directions of wrist motion for four experimental conditions: intact, and after sequential sectioning of the SLIL, DIC, and LRL. Sectioning the SLIL alone did not change wrist ROM in any direction (p>0.10), while sectioning the SLIL and both the DIC and LRL caused significant increases in radial deviation, radial-extension, and ulnar-flexion ROM (p<0.05). The COR of the intact wrist was located between the proximal third and middle third of the capitate, depending on the direction of wrist motion. While SLIL sectioning alone did not affect the COR, subsequent DIC sectioning led to a distal shift of COR in motions involving ulnar-extension relative to the intact condition. Additional sectioning of the LRL caused a proximal shift of COR in motions involving radial-flexion. A proximal shift implies a more dominant role of the radiocarpal joint, while a distal shift of the COR implies an increased role for the midcarpal joint. Understanding the role of ligaments on overall wrist mechanics is critical to devising new treatment strategies to restore wrist function.

1. Introduction

The stability of the wrist joint is driven by the articular geometry of the eight carpal bones and the constraints of the connecting ligaments (Berger, 1993). Ruptures to the interosseous ligaments in the wrist can affect wrist function during occupational and daily living activities, leading to abnormal joint forces that predispose to post-traumatic arthritis. Changes in wrist stability can be detected if ligament rupture results in changes in carpal bone posture or kinematics. However, there is considerable debate regarding the role that individual ligaments play in stability of the wrist (Short et al., 2002, 2005).

The scapholunate interosseous ligament (SLIL) is the most commonly injured wrist ligament and the primary stabilizer of the scapholunate joint (Kitay and Wolfe, 2012). It has been demonstrated that isolated SLIL tears are insufficient to cause postural changes in the proximal carpal row (Pérez et al., 2019; Ruby et al., 1987; Short et al., 2002). Cadaveric studies by Short and colleagues have demonstrated that sectioning both the SLIL and scaphotrapeziotrapezoid ligaments caused minimal changes in scaphoid and lunate rotation under load, but did not result in dorsal intercalated segment instability (DISI) (Short et al., 2005, 2002). Elsaidi et al. demonstrated that an intact dorsal intercarpal ligament (DIC) and its dorsal capsular attachments to the scaphoid prevented rotary subluxation of the scaphoid after SLIL disruption (Elsaidi et al., 2004). In a recent study by Pérez et al., sectioning of the DIC and volar long radiolunate ligament (LRL) in the SLIL-deficient wrist were sufficient to produce an angular change of 15 degrees or more in lunate sagittal alignment (DISI) (Pérez et al., 2019).

In the studies highlighted above, the role of ligaments were studied with a focus on the kinematics or posture of individual carpal bones. However, an understanding of the impact of these ligamentous constraints on global wrist motion and the wrist’s center of rotation are additional kinematic properties which must be considered to gain a full understanding of ligament injury. Experimental protocols for evaluating wrist motion have ranged from the use of wrist motion simulators to tendon-loading protocols employing dead weights. Kinematic measurements have been performed using motion capture systems, fluoroscopy or plain radiographs (Loisel et al., 2020; Padmore et al., 2019; Pérez et al., 2019; Short et al., 2002). Typically, these experiments are performed in serial static positions or at smaller wrist rotations.

The availability of robotic testing allows us to dynamically simulate large wrist rotations that closely resemble occupational and recreational activities. We have developed a hybrid load-displacement robotic wrist testing protocol with a mobile axis of rotation (Badida et al., 2020) that simultaneously allows wrist joint translations; this permits a more complete evaluation of kinematic changes following ligament sectioning. The system’s ability to record torques in all rotational degrees-of-freedom (DOF) enables us to deconstruct the mechanics of the wrist in all directions of wrist motion.

The purpose of this study was to evaluate acute changes in global wrist range-of-motion (ROM) and center of rotation (COR) after sequential sectioning of three important stabilizing ligaments – the SLIL, DIC, and LRL. We hypothesized that wrist ROM would increase incrementally in all directions of wrist motion with each ligament sectioned. We further hypothesized that the COR of the wrist, which has been shown to be located in the proximal pole of the capitate in intact wrists (Akhbari et al., 2020; Neu et al., 2001), would shift proximally with each ligament sectioned.

2. Methods

2.1. Specimen Preparation and Imaging

Nine fresh-frozen, male, right upper-extremities (average: 58 yrs., range: 44-67 yrs.) were confirmed to be free of traumatic defects or inflammatory bone changes using fluoroscopy. The specimens were thawed to room temperature prior to use. The specimen preparation, computed tomography (CT) imaging and generation of three dimensional bone models were implemented as described previously (Badida et al., 2020). Point coordinates of the anatomical landmarks on the radius and metacarpals and their respective fiducial markers were digitized on the bone models using Geomagic Wrap (3D Systems^®, NC, US). The anatomical and fiducial landmarks utilized for registration and transformation of anatomical coordinate systems from CT images (CT_GCS) to the robot’s global coordinate system (ROB_GCS) were identified as described previously (Badida et al., 2020).

The surface models of the third metacarpal and capitate were used to calculate bone lengths and revised carpal height ratios (Nattrass et al., 1994). Revised carpal height ratio is defined as the carpal height divided by the capitate length. Carpal height was defined as the distance between the articular surface of the radius and the most distal point on the surface of the capitate (i.e., the proximal-distal distance between their coordinate systems).

2.2. Ligament Sectioning

We studied a single ligament sectioning sequence: 1) SLIL, 2) DIC, and 3) LRL (Figure 1). Each specimen was tested intact and then again after each ligament was cut. The SLIL ligament was sectioned through a 3 cm capsular incision just distal to the Lister’ tubercle. The dorsal, volar, and proximal components of the SLIL were sectioned using a number 15-blade under direct visualization. The SLIL was sectioned from the scaphoid to avoid inadvertent sectioning of the LRL. A Freer elevator was used to ensure full release of the ligament, paying particular attention that the complete volar and distal segments were completely incised. The technique used to section the DIC ligament involved a number 11-blade and the same capsular incision used to access the SLIL. The lunate insertion of the DIC was sectioned first. The blade was introduced with the sharp edge oriented towards the interval between the DIC and dorsal radiocarpal (DRC) ligaments and the cut was performed tangential to the surface of the lunate bone, thus avoiding injury to the lunate insertion of DRC. This was followed by sectioning the insertions of the DIC on the proximal pole and ridge of the scaphoid. The DIC was also sectioned from its insertion on the dorsal SLIL through the DCSS (dorsal capsuloligamentous scapholunate septum). Finally, the LRL ligament was sectioned through a small modified volar approach. The volar radiocarpal wrist capsule was identified through a longitudinal incision through the floor of the flexor carpi radialis tendon sheath. The volar capsule was incised at the space of Poirier and the LRL was visualized. The ligament was then carefully isolated from the radioscaphocapitate (RSC) and short radiolunate (SRL) ligaments and cut at its radial insertion.

Figure 1.

The scapholunate interosseous ligament (SLIL), dorsal intercarpal ligament (DIC), and long radiolunate ligament (LRL) were sectioned sequentially. The SLIL was sectioned from the scaphoid, the DIC ligament was sectioned using the same capsular incision used to access the SLIL. The lunate insertion of the DIC was sectioned first, followed by sectioning its insertions on the proximal pole and waist of the scaphoid. The LRL ligament was sectioned at the radial insertion.

2.3. Kinematic Data Acquisition

The wrists were tested using a 6-DOF robotic musculoskeletal simulator using our published hybrid-control protocol (Badida et al., 2020). Briefly, the robot (KUKA KR6 R700, Augsburg, DE), equipped with a 6-DOF load cell (ATI, Apex, NC) and controlled by simVITRO software (Cleveland Clinic, OH), was used to move the wrist through its envelope of motion. The radius and ulna were mounted to the robot’s fixed base and the metacarpals were attached to the robot end-effector (Figure 2). A 6-DOF digitizing probe (Optotrak, NDI, Ontario, CA) was used to establish the location and orientation of the load cell and the specimen in the robot test space. The fiducial holes (3.5 mm dia., x ~ 10 mm deep) drilled into the radius and metacarpal potting were digitized to register the anatomical points from the CT_GCS to the ROB_GCS. These anatomical points were subsequently used to generate the radius coordinate system (RCS) and the metacarpal coordinate system (MCS) using the simVITRO software. The starting position of the wrist was defined at: (1) 0° of flexion-extension and 0° radial-ulnar deviation of the MCS with respect to the RCS; (2) 0 Nm of pronation-supination torque; and (3) 0 N of load at the joint in all three directions (volar/dorsal, radial/ulnar, and compression/distraction).

Figure 2.

Illustration of the experimental setup on the robotic musculoskeletal simulator depicting typical mounted wrist specimen and coordinate systems. The proximal forearm (radius and ulna) is mounted to a raised pedestal on the fixed base and the distal metacarpals are secured to the robot end effector. The anatomical coordinate systems of the radius (X_R, Y_R and Z_R) and metacarpals (X_M, Y_M, Z_M) are defined in the robotic test space. The radius coordinate system (RCS) is defined as: Z_R – positive radially, defined by base of concavity of sigmoid notch (SN) and radial styloid (RS); Y_R – positive proximally, defined by the most distal point on the line fit through centroids of radial diaphysis (RC) and the projection of RC on distal articular surface of radius (RI); X_R – positive volarly, defined by crossing Y_R and Z_R. The metacarpal coordinate system MCS is constructed as: Y_M—positive proximally, defined by the distal-most point on the line fit through centroids of 3^rd metacarpal (M1) and the proximal-most point on the line fit through centroids of 3^rd metacarpal (M2); Z_M—positive radially, defined by the centroid at the base of 2^nd metacarpal (M3) and the centroid at the base of 4^th metacarpal (M4); X_M—positive volarly, generated by crossing Y_M and Z_M; and the origin, O_M, defined as the midpoint of M3 and M4. Figure reprinted with permission from (Badida et al., 2020), Copyright© 2020 by ASME.

The wrists were rotated in 24 directions: the anatomical directions of flexion, extension, radial and ulnar deviation, and 20 coupled directions at 15° intervals between the anatomical motions. Pronation and supination were constrained to 0° and joint forces were set to 0 N for all three directions. The wrists were rotated at a rate of 1°/sec, and motion was terminated at a resultant torque of 2 Nm, defined as the root-mean square (RMS) of all three torque components (Crisco et al., 2011). Each wrist was tested in the following sequence: intact, SLIL ligament sectioned (SLIL), DIC ligament sectioned (SLIL+DIC), and LRL ligament sectioned (SLIL+DIC+LRL). Approximately 7% of all tests (60 /864) from all specimens and test conditions were terminated between torque values of 1.5 Nm and 2 Nm due to the limits of the robot’s working envelope of motion.

The joint rotations were position-controlled, and their starting positions were consistent throughout. The joint translations were force-controlled by setting the forces to 0 N throughout the experiment. Therefore, in certain instances, the robot did not adjust the translations to 0 mm, and the starting position varied. To ensure a consistent starting position for testing after each ligament was sectioned, carpal height after each ligament sectioning was assessed for all specimens. Carpal height was computed at the starting positions for each condition of ligament and direction of wrist motion by calculating the proximal-distal distance between the proximal surface of the third metacarpal and the articular surface of the radius. The change in carpal height in the proximal-distal direction was compared to the starting position of the neutral posture of the intact condition for each of the ligament sectioning positions, and changes of more than 20% were defined as abnormal movements. The 20% limit (i.e., allowing for up to 7 mm movement compared to the neutral pose) was chosen to ensure the revised carpal height ratio was consistent between conditions and among all subjects. Overall, ligament sectioning led to 20% height reductions in only 8.4% wrist postures, and those conditions were removed from further analysis. All 9 specimens passed this criterion for the intact and SLIL-sectioned cohorts, 8 specimens passed the criteria after DIC sectioning, and 7 specimens passed after additional LRL sectioning.

2.4. Data Processing

Wrist rotation was calculated as the flexion-extension (FE) and radial-ulnar deviation (RUD) angles of the third metacarpal with respect to the radius, relative to the neutral position mentioned above. The motion was computed using a Z-X-Y Cardan angle sequence and wrist rotations were calculated as $\sqrt{{\left(FE\right)}^2+{\left(RUD\right)}^2}.$ The loading portion of the torque-rotation curves were fit with 5^th order polynomials (MATLAB, Mathworks, US) and the ROM and neutral zone (NZ) values were calculated as rotations at torque values of 2 Nm and 0.5 Nm, respectively (Crisco et al., 2011). The neutral zone values reflect joint rotations for which there is negligible stiffness (Crisco et al., 2011). In the tests terminated before 2 Nm, the ROM values were estimated via extrapolation of the fitted curves. The directions and lengths of the principal axes of the motion envelopes for the four experimental conditions were calculated from best-fit ellipses passing through the ROMs in all 24 directions using least squares criterion. The mean squared errors (MSEs) of the calculated best-fit ellipses were less than 0.04° in all cases, demonstrating the robustness of the fitting. Finally, the aspect ratios of the best-fit ellipses were computed (^{major axis length}/_{minor axis length}) to describe the overall shapes of the envelopes of motion.

The proximal-distal location of the projected COR of the wrist at the maximum wrist rotation (ROM) was defined by the shortest distance between the screw axis of motion and the proximal-distal axis of the radius in the radius CS (Akhbari et al., 2020). The three-dimensional orientation of the screw axis was computed using the helical axis of motion method (Crisco et al., 2005), and the shortest distance between the screw axis and the proximal-distal axis of the radius was determined. The shortest distance was calculated as the length of the line perpendicular to both the screw axis and the proximal-distal axis of the radius. The point where the shortest distance intersected the proximal-distal axis of the radius was defined as the COR, and the location of the COR was calculated for all 24 directions of the wrist’s ROM envelope.

2.5. Statistical Analysis

One-way repeated measures ANOVAs (GraphPad Prism v8.4, GraphPad, San Diego, California) with Bonferroni pairwise comparisons were used to determine if the wrist envelope aspect ratios and orientations, maximum ROMs, and (NZs) differed for the four test conditions (intact, SLIL, SLIL+DIC, and SLIL+DIC+LRL). The ROM and NZ from the four directions of flexion, extension, and radial and ulnar deviation, and the coupled dart thrower’s directions of ulnar-flexion and radial-extension (15°, 30°, 45°, 60°, and 75° off flexion and extension, respectively), were compared within each of the ligament sectioning conditions using a mixed-effects model with additional Tukey post-tests (p-value < 0.05).

3. Results

3.1. Wrist Range-of-Motion and Neutral Zone

The elliptical shape of the wrist ROM envelope, as measured by its aspect ratio, was unchanged following ligament sectioning (p=0.975) (Figure 3). The aspect ratio of the ROM ellipses was similar throughout different conditions, with the lowest for the intact condition and largest for SLIL+DIC+LRL condition. The mean orientation of the ROM envelope was similar for all conditions (p=0.05) (Table 1) and oriented towards ulnar flexion.

Figure 3.

The average range-of-motion (ROM) envelopes for all conditions. The point-to-point elliptical shape of the ROM envelope was preserved following ligament sectioning; however, the magnitude of the ROM did increase after sequential sectioning of all three ligaments. The ROM envelope was oriented towards ulnar flexion by 9.9° ± 2.0° in the intact state, 11.5° ± 2.0° post SLIL sectioning, 11.8° ± 2.1° post SLIL+DIC sectioning, and 13.2° ± 2.8° post SLIL+DIC+LRL sectioning and was statistically not significant (p=0.0543).

Table 1.

Orientation (degrees) of the principal axis of the range-of-motion (ROM) envelope for all conditions. The orientation increased approximately 1.6° after SLIL sectioning, to 1.9° after SLIL+DIC sectioning, and 3.3° after SLIL+DIC+LRL sectioning.

Specimen	Condition
	Intact	SLIL	DIC+SLIL	LRL+DIC+SLIL
S1	5.9	11.5	12.1	12.8
S2	9.2	12.3	14.4	17.5
S3	8.8	12.4	9.5	11.3
S4	10.5	16.1	13.1	12.8
S5	10.4	8.9	-	8.7
S6	8.6	11.0	13.3	14.6
S7	11.7	10.7	13.4	14.4
S8	10.6	10.2	8.9	-
S9	12.9	10.1	9.6	-
MEAN (SD)	9.9 (2.0)	11.5 (2.0)	11.8 (2.1)	13.2 (2.8)

There were no significant changes in the magnitude of wrist ROM in any direction of motion after SLIL sectioning alone (Figure 4, A). However, subsequent sectioning of the DIC increased the average wrist ROM relative to intact by 3.9° in radial deviation (p=0.05), by 8.8° in the radial-extension region (p=0.01 to p=0.04), and by 13° in ulnar-flexion (p=0.002 to p=0.05) (Figure 4, B). Adding LRL sectioning increased the average wrist ROM to 20° in ulnar-flexion (p<0.0001 to p=0.003), to 15° in radial-extension (p=0.01 to p=0.04), to 9.6° in radial deviation (p=0.01), and to 11° in radial-flexion (p=0.005 to p=0.03), compared to intact (Figure 4, C). LRL sectioning resulted in a 7.5° increase in ROM in ulnar-flexion compared to the SLIL+DIC condition (p=0.03). The area of the ROM envelope also increased significantly after sectioning the SLIL, DIC, and LRL ligaments. SLIL, SLIL+DIC, and LRL+SLIL+DIC sectioning resulted in 13.4±8.7% (p=0.003), 26.4±7.6% (p=0.0017), and 39.5±12.8% (p=0.0001) increases in ROM envelope area, compared to the intact condition, respectively.

Figure 4.

The difference in ROM envelopes with respect to the intact condition. The average (solid lines) and 95% confidence intervals (dashed lines) represent the change in magnitude of the range-of-motion (ROM) envelope after sequential sectioning of ligaments. Significant differences (p<0.05) along with the p-values are shown with * in each direction.

In contrast to the shape of the ROM envelopes, the elliptical shape of the NZ envelope did not change significantly (p=0.85) with sectioning of the ligaments. The magnitude of the NZ envelope increased only in extension, and only after SLIL+DIC+LRL sectioning compared to the intact wrist (p=0.04).

3.2. Center of Rotation

The COR of the intact wrist was located on the proximal surface of the capitate in flexion/extension, and proximal to the mid-capitate in radial/ulnar deviation (Figure 5). Overall, sectioning of the SLIL ligament alone did not change the location of the COR appreciably compared to the intact condition (Figure 6, left). However, the subsequent sectioning of the DIC shifted the average COR distally by ~1.5-2 mm (from ~12 mm to ~13.5-14 mm) in ulnar-extension directions of motion compared to the intact condition (Figure 6, middle). Similarly, the subsequent sectioning of the LRL resulted in an ~3 to 3.7 mm proximal shift of COR in radial-flexion and flexion directions of motion from the intact condition. LRL sectioning also led to a 1.5 mm proximal shift in the COR during wrist extension (p=0.01), and a 1.5 to 1.6mm proximal shift during radial-extension (p<0.02) from the SLIL+DIC condition.

Figure 5.

The centers of rotations (COR) for the four primary motions of extension, ulnar deviation, flexion, and radial deviation are plotted on images of the capitate and radius, illustrating the relationship between the location of the COR and the capitate. The COR for all other directions of wrist motions are similarly plotted, but without the bone images. The dashed circles depict the relative locations of the radius surface and the most proximal and distal extents of the capitate. In the intact condition, the COR was located at the proximal surface of the capitate in flexion-extension, and it shifted distally to the center of the proximal pole of the capitate in radial-ulnar deviation. After each ligament was sectioned, the COR shifted proximally in wrist flexion and radial flexion, while it moved distally in ulnar-extension.

Figure 6.

The average (solid lines) and 95% confidence intervals (dashed lines) for the change in center of rotation (COR) location after each ligament was sectioned, compared to the intact condition. Overall, the COR location was not affected by scapholunate interosseous ligament (SLIL) sectioning alone, while a distal shift of the COR in the ulnar-extension was observed after dorsal intercarpal ligament (DIC) sectioning. Long radiolunate ligament (LRL) sectioning resulted in a proximal shift of the COR in motions involving radial-flexion. Significant differences are denoted with an * and p-value.

4. Discussion

The objective of our study was to evaluate acute changes in global wrist ROM and COR after sequential sectioning of three important stabilizing ligaments: the SLIL, DIC, and LRL. We assessed the effect of this single ligament sectioning sequence on wrist kinematics using a robotic system. We found that cutting these ligaments did not change the oblique orientation of the ROM envelope. We observed that sectioning the SLIL alone did not change the overall wrist ROM, while sectioning the SLIL, DIC, and LRL increased radial deviation, radial-extension, radial-flexion, and ulnar-flexion significantly. The role of the LRL was also important in radial-flexion, as ROM increased significantly compared to the intact after sectioning of the LRL ligament. SLIL sectioning did not affect the COR location, while DIC sectioning caused a distal shift of COR in ulnar-extension motions and LRL sectioning caused a proximal shift of COR in radial-flexion motions.

The orientation of the motion envelope in our study was similar to that of intact wrists reported previously (Badida et al., 2020; Crisco et al., 2011). The ROM and NZ elliptical shape and orientation were preserved following sectioning of each ligament, although the area of the ROM envelope increased significantly after each ligament sectioning. The preservation of the motion envelope orientation indicates that global DTM is preserved, even after sequential SLIL, DIC, and LRL sectioning, and that DTM is largely independent of these three ligaments.

Previous studies (Padmore et al., 2019; Pérez et al., 2019; Short et al., 2002) have shown that the scaphoid flexes during wrist flexion or radial deviation, and its intact SLIL guides the lunate into flexion. Our study confirmed previous studies that did not observe any changes in wrist ROM after SLIL sectioning, indicating that although the kinematics between the lunate and scaphoid may be slightly altered after SLIL sectioning (Short et al., 2002), global wrist motion may be preserved acutely by the “critical stabilizers” of the proximal row (Pérez et al., 2019). In our study, additional cutting of the DIC significantly influenced ROM in radial deviation, radial-extension, and ulnar-flexion, while LRL sectioning significantly increased radial-flexion.

The location of the wrist COR and its dynamic movement provide insight into the role of ligaments in stabilizing the radiocarpal and midcarpal joints of the wrist. Similar to previous studies (Akhbari et al., 2020; Neu et al., 2001; Rainbow et al., 2013), we observed the COR of the intact wrist lies on the capitate’s proximal surface in flexion-extension (i.e., midcarpal joint) and about mid-capitate in radial-ulnar deviation. Compared to the intact wrist, a proximal shift of the COR reflects the more dominant role of the radiocarpal joint in overall wrist motion, while a distal shift of the COR relative to its intact location reflects the role of the midcarpal joint in overall wrist motion. In this study, there was a trend towards a proximal shift of the COR in motions of radial-flexion and a distal shift of the COR in motions of ulnar-extension with ligament sectioning. Although we only observed a significant proximal shift of the COR in wrist flexion motions after LRL sectioning, this trend suggests these ligaments influence how the wrist’s motion is dependent on the relative contributions of the radiocarpal joint and midcarpal joint.

As with all in vitro studies, ours had several limitations that affect the generalizability of our results. First, because our study was performed as a time-zero biomechanical study, our results only reflect acute changes in wrist kinematics. More profound changes may occur when additional supporting ligaments attenuate over time due to altered kinetics. Second, we only measured changes in overall wrist motion, so we cannot comment on the direct effect of ligament sectioning on individual carpal bone kinematics. It is possible that while the changes in wrist motion we observed were relatively modest, there could be significant underlying changes in carpal bone motion with ligament disruption that would lead to abnormal joint loading and cartilage changes. Future investigations using marker-based motion tracking in conjunction with our robotic system, would provide insight into ligament sectioning-related carpal kinematic abnormalities. Third, our conclusions reflect a single ligament cutting sequence of SLIL, DIC, and LRL. Different sectioning sequences might allow us to better understand the role of each ligament separately. Our selection of the SLIL, DIC, and LRL ligaments and the specific sectioning sequence was based on the rationale that SLIL tears, along with DIC and LRL tears, produce DISI (Pérez et al., 2019), while disruption of other secondary ligaments like SRL and RSC do not cause acute DISI (Padmore et al., 2019; Short et al., 2005). Finally, all our specimens were from male donors. It is possible that the results might differ with specimens from female donors. However, our focus was on studying the role of SLIL, DIC, and LRL ligaments in overall wrist mechanics and not on determining possible sex-related differences.