Motion analysis of the thumb and the four fingers during human gripping of a cylindrical object is a prerequisite for designing motion mechanisms in electronic arm prostheses and robotic hands. Conventional measurement methods include the use of angle sensors or multiple video recording of markers. In the present study, we performed X-ray computed tomography (CT) imaging on fingers gripping cylinders of three different diameters (10, 60, and 120 mm) and constructed a bone model based on these CT images to directly measure the flexion angle of each finger joint. We then compared the results with the flexion angles of joints measured using other methods. The subjects comprised 10 Japanese men with no hand injuries or diseases. Our results showed that smaller cylinder diameters were associated with significant increases in the flexion angle of all the joints of the four fingers. When focusing on the distal interphalangeal joint (DIP), there was no significant difference between any of the fingers for each of the cylinders, except between the index and middle fingers for the 10 mm-diameter cylinder. When focusing on the 10 mm-diameter cylinder, the flexion angle of the proximal interphalangeal joint (PIP) of each finger was significantly larger than that of the DIP and metacarpophalangeal joint (MP). However, no such significant difference was noted for the 120 mm-diameter cylinder. The coupling ratio (CR), which is the ratio of the flexion angles of the DIP and PIP, was significantly smaller for the 10 mm-diameter cylinder than for the 60 mm-diameter cylinder. However, there were no significant differences in CR between any of the fingers. A comparison of our study results with those derived using other methods indicated quantitative consistency for the DIP and PIP. However, for the MP, we noted differences that may be explained by the difficulty in determining the longitudinal axis of the metacarpal using other methods.
Several studies have investigated the gripping of an object by human fingers. Napier [
When designing motion mechanisms for electronic arm prostheses and humanoid fingers (robotic hands), it is important to evaluate motion analysis of the thumb and the four fingers when a person grips a cylindrical object. Moreover, human motion data are crucial in enabling such devices to perform human-like finger movements. The use of an actuator for each joint would result in a bulky and intricate electronic arm prosthesis. Therefore, coordinated coupling between joints should be considered to reduce the number of actuators [
Studies have used different methods to measure the joint angles of the thumb and the four fingers while gripping a cylinder. Some of these methods employed an angle sensor attached to the back of the hand [
In this study, we performed X-ray CT imaging on the hands gripping cylinders with three different diameters and constructed bone models for the distal phalanx, middle phalanx, and proximal phalanx and for the second to fifth metacarpal of the four fingers excluding the thumb. We measured the flexion angle of each joint and compared the results with the flexion angles measured by other researchers using other methods.
The subjects comprised 10 Japanese men with no hand injuries or diseases, with ages ranging from 21 to 25 years, mean height of
Cross-sectional images distal from the midshaft of the forearm (spatial resolution:
CT imaging positions and three-dimensional bone models. (a) Basic position, (b) gripping a 10 mm-diameter cylinder, (c) gripping a 60 mm-diameter cylinder, and (d) gripping a 120 mm-diameter cylinder.
Open source software (3D Slicer; ver. 4.5) for visualizing medical images was used to construct the three-dimensional bone models based on CT images of all bones distal from the distal portions of the radial and ulnar visually (Figure
Bone models for each cylinder gripped were used to measure the flexion angles of the distal interphalangeal joints (DIPs), proximal interphalangeal joints (PIPs), and metacarpophalangeal joints (MPs) of the four fingers (index, middle, ring, and little). The thumb was excluded from the measurements because the location of the thumb varies greatly among individuals when gripping a cylindrical object. For example, we used the following method to calculate the flexion angle of the PIP of the index finger (Figure
Method for calculating the flexion angle of the PIP. Direction vectors from the center of the proximal base to the center of the distal head of the middle phalanx and proximal phalanx were calculated, and the angle created by these two direction vectors was considered to be the flexion angle of the PIP.
When gripping an object, both the DIP and PIP are flexed. However, it has been reported that the flexion angle proportions of these joints are independent of the size of the object [
A three-way ANOVA with repeated measurement (
Three-way ANOVA with repeated measurement (
Source of variation | Degree of freedom | Type III SS | Mean squares | ||
---|---|---|---|---|---|
Diameters |
1.149 | 207,673.697 | 180,797.809 | 1025.177 | <0.001 |
Fingers |
3 | 4014.324 | 1338.108 | 27.279 | <0.001 |
Joints |
2 | 26,868.242 | 13,434.121 | 28.683 | <0.001 |
6 | 2151.941 | 358.657 | 12.524 | <0.001 | |
2.301 | 19,652.346 | 8542.455 | 23.408 | <0.001 | |
6 | 2653.076 | 442.179 | 6.792 | <0.001 | |
12 | 2488.546 | 207.379 | 3.036 | 0.001 |
aDiameters—10 mm, 60 mm, and 120 mm. bFingers—index, middle, ring, and small. cJoints—DIP, PIP, and MP. SS: sums of squares.
A two-way ANOVA with repeated measurement (
Table
Mean flexion angle of each joint from the index to the little finger when cylinders of the different diameters were gripped. Numbers in the lower brackets indicate standard deviation.
Diameter | Index (deg) | Middle (deg) | ||||
DIP | PIP | MP | DIP | PIP | MP | |
10 mm | 48.2 |
105.5 |
65.6 |
64.8 |
104.8 |
75.9 |
60 mm | 35.2 |
48.0 |
39.7 |
34.5 |
48.1 |
46.3 |
120 mm | 18.9 |
24.2 |
32.2 |
20.0 |
25.9 |
22.9 |
Diameter | Ring (deg) | Small (deg) | ||||
DIP | PIP | MP | DIP | PIP | MP | |
10 mm | 57.2 |
110.5 |
76.6 |
65.8 |
93.0 |
64.1 |
60 mm | 27.1 |
48.7 |
38.7 |
30.0 |
32.8 |
35.2 |
120 mm | 16.1 |
24.7 |
15.1 |
11.9 |
15.2 |
12.6 |
Table
Comparison | Index | Middle | ||||
DIP | PIP | MP | DIP | PIP | MP | |
0.155 |
||||||
0.084 |
||||||
Comparison | Ring | Small | ||||
DIP | PIP | MP | DIP | PIP | MP | |
Significance level:
Table
Comparison | Diameter 10 mm | Diameter 60 mm | Diameter 120 mm | ||||||
---|---|---|---|---|---|---|---|---|---|
DIP | PIP | MP | DIP | PIP | MP | DIP | PIP | MP | |
1.0 |
1.0 |
1.0 |
0.391 |
1.0 |
1.0 |
||||
0.551 |
1.0 |
0.729 |
0.10 |
1.0 |
1.0 |
1.0 |
1.0 |
||
0.084 |
0.128 |
1.0 |
0.661 |
0.874 |
0.065 |
0.162 |
|||
0.353 |
0.704 |
1.0 |
0.191 |
1.0 |
0.302 |
1.0 |
1.0 |
||
1.000 |
0.65 |
0.071 |
0.097 |
0.108 | |||||
0.861 |
0.382 |
1.0 |
0.510 |
0.705 |
0.348 |
1.0 |
Significance level:
Table
Comparison | Index | Middle | ||||
10 mm | 60 mm | 120 mm | 10 mm | 60 mm | 120 mm | |
0.050 |
0.508 |
0.958 | ||||
0.125 |
0.636 |
0.148 |
0.840 | |||
0.538 |
0.057 |
1.0 |
1.0 | |||
Comparison | Ring | Small | ||||
10 mm | 60 mm | 120 mm | 10 mm | 60 mm | 120 mm | |
0.095 |
1.0 |
0.536 | ||||
0.06 |
1.0 |
1.0 |
0.713 |
1.0 | ||
0.343 |
0.195 |
1.0 |
1.0 |
Significant level:
Table
Coupling ratio (CR), the ratio of the flexion angles of the DIP and PIP.
Diameter | Index | Middle | Ring | Small | All |
---|---|---|---|---|---|
10 mm | 0.47 (0.24) | 0.62 (0.16) | 0.52 (0.16) | 0.73 (0.18) | 0.58 |
60 mm | 0.77 (0.29) | 0.75 (0.26) | 0.58 (0.21) | 1.10 (0.67) | 0.80 |
120 mm | 0.85 (0.41) | 0.96 (0.98) | 0.73 (0.44) | 0.97 (0.67) | 0.88 (0.65) |
All | 0.70 (0.35) | 0.78 (0.59) | 0.61 (0.30) | 0.93 (0.56) | 0.75 (0.48) |
Several studies have measured the flexion range of motion (ROM) of each finger joint [
Several studies have also measured the flexion angles of each finger when gripping a cylinder. Lee and Rim [
Figure
A comparison of flexion angles measured in our study with those measured in Takano et al.’s and Gülke et al.’s studies [
DIP
PIP
MP
Figure
A comparison of the CR obtained in our study with those reported by other researchers.
Index
Little
Table
Several limitations accompany the measurement of the flexion angle using X-ray CT imaging. First, this technique is a low invasive measurement because of the use of X-ray. This makes it difficult to perform measurements in several different conditions on each subject. Therefore, the radiation dose (
In the present study, we performed X-ray CT imaging on fingers gripping cylinders of three different diameters (10, 60, and 120 mm) and constructed a bone model based on these CT images to directly measure the flexion angle of each finger joint. Our results showed that smaller cylinder diameters were associated with significant increases in the flexion angle of all the joints of the four fingers. When focusing on the 10 mm-diameter cylinder, the flexion angle of the PIP of each finger was significantly larger than that of the DIP and MP. However, no significant difference was noted for the 120 mm-diameter cylinder. The coupling ratio (CR), which is the ratio of the flexion angles of the DIP and PIP, was significantly smaller for the 10 mm-diameter cylinder than for the 60 mm-diameter cylinder. However, there were no significant differences of the CR between any of the fingers.
The data used to support the findings of this study are included within the article. The CT data used to support the findings of this study have not been made available because of privacy protection.
The authors declare that there are no conflicts of interest regarding the publication of this paper.
This work has been supported by the Research Fund of Utsunomiya University (172118).