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Research Papers

Determining Functional Finger Capabilities of Healthy Adults: Comparing Experimental Data to a Biomechanical Model

[+] Author and Article Information
Samuel T. Leitkam

Department of Mechanical Engineering,
Michigan State University,
East Lansing, MI 48824

Tamara Reid Bush

Department of Mechanical Engineering,
Michigan State University,
East Lansing, MI 48824
e-mail: reidtama@msu.edu

Laura Bix

School of Packaging,
Michigan State University,
East Lansing, MI 48824

1Corresponding author.

Contributed by the Bioengineering Division of ASME for publication in the Journal of Biomechanical Engineering. Manuscript received August 30, 2013; final manuscript received November 19, 2013; accepted manuscript posted December 16, 2013; published online February 5, 2014. Editor: Beth Winkelstein.

J Biomech Eng 136(2), 021022 (Feb 05, 2014) (11 pages) Paper No: BIO-13-1397; doi: 10.1115/1.4026255 History: Received August 30, 2013; Revised November 19, 2013; Accepted December 16, 2013

The human hand has a wide range of possible functional abilities that can change with age, disease, and injury, and can vary from individual to individual and subsequently can affect a person's quality of life. The objective of this work was to develop a theoretical model of the space that is reachable by the hand, weighted to represent three types of functionality, and to compare this model to an experimental data set obtained from a healthy hand population. A theoretical model, termed the Weighted Fingertip Space, was developed using 50th percentile published hand data and ranges of finger motion. The functional abilities calculated in the model were the abilities to position the fingertip pad, orient the fingertip pad, and apply directional forces through the fingertip pad at all the reachable points in space with respect to the palm. Following the development of this theoretical model, experimental data sets from nine individuals with healthy hands were obtained through motion capture techniques. The experimental data were then compared to the theoretical model. Comparisons between a 50th percentile theoretical model and a subject with a similar sized hand showed good agreement in weighting parameters and overall size and shape of the model spaces. The experimental data set from the entire sample, which ranged from the 2nd to 95th percentile hand sizes, showed resultant models that, on average, reached smaller volumes of space, but yielded higher values of the functional measures within those volumes. Additionally, in comparison to the theoretical model, the variability of the experimental models showed that small changes in hand dimensions and ranges of motion of the finger joints had a large influence in the functional measures of the model. Combined, these results suggest that the modeling technique can calculate functional ability of the hand, but should be used on an individualized basis for evaluating changes in function (e.g., rehabilitation). Further, scaling to hand size has the potential to yield “average” models for larger population samples.

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References

Figures

Grahic Jump Location
Fig. 3

Diagram of the three possible FADs for a fingertip position/orientation of the second digit. Each position, force direction, and movement arc are coordinated by shades of gray.

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Fig. 4

Visual representation of the possible fingertip pad positions and orientations of the second digit calculated in the WFS, shown as a plane bisecting the second digit. Red dots indicate the fingertip pad positions, while black lines indicate the normal direction pointing out of the face of the fingertip pad at those points. Only 1000 points are shown for clarity, and the gray finger shown in background is included to show orientation in space with respect to the hand.

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Fig. 5

Clustered WFS where the position points and orientation vectors have been grouped to the nearest mesh point. Red dots indicate the rounded fingertip pad positions, while black lines indicate the normal directions pointing out of the face of the fingertip pad at those points. Finger orientation is the same as depicted in Fig. 4.

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Fig. 6

Hand with marker pods used for calculation of finger joint ROMs

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Fig. 8

3D plot of FAD Range weighting values for the second digit (left) and the whole hand (right) of the theoretical model. The reachable points for digits two through five all assume a similar shape, while the reachable points for the thumb arc from right to left across the other fingers' reachable spaces.

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Fig. 7

Local coordinate systems shown for second digit. Subscripts refer to the rigid body that the coordinate system is attached to PP = proximal phalange, MP = middle phalange, DP = distal phalange.

Grahic Jump Location
Fig. 9

Sagittal plane plots of the model based on the Number of Ways to Reach weighting at each point in the theoretical 50th percentile male WFS model (a) and the WFS model from the experimental data of the participant nearest to a 50th percentile hand size (b). The plots are shown at the level of the second MCP joint. The reachable points are plotted in a color scale where red indicates points in space that are reachable in >30 ways while blue indicates points that are reachable in <10 ways.

Grahic Jump Location
Fig. 2

Thumb CMC motion terminology. The zenith axis was a line parallel to the long axis of the hand and running through the center of the CMC joint. The inclination angle (ζ) was the angular amount of rotation of the thumb away from the zenith axis. The azimuth angle (γ) was the angular amount of rotation of the thumb about the zenith axis where 0 deg indicated the thumb being in the plane of the hand.

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Fig. 1

Hand dimensions used for the rigid bodies of the model. The dimensions for rigid bodies of digits three through five were taken similarly as those shown for digit two.

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Fig. 10

Sagittal plane plots of the model based on the Fingertip Orientation Range weighting at each point in the theoretical 50th percentile male WFS model (a) and the WFS model from the experimental data of the participant nearest to a 50th percentile hand size (b) at the level of the second MCP joint. The reachable points are plotted in a color scale where red indicates points in space that have a range >35 deg of possible fingertip orientations while blue indicates points that have a range <10 deg of possible fingertip orientations.

Grahic Jump Location
Fig. 11

Sagittal plane plots of the model based on the FAD Range weighting at each point in the theoretical 50th percentile male WFS model (a) and the WFS model from the experimental of the participant nearest to a 50th percentile hand size (b) at the level of the second MCP joint. The reachable points are plotted in a color scale where red indicates points in space that have a range >100 deg of possible FADs while blue indicates points that have a range <40 deg of possible FADs.

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