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TECHNICAL BRIEF

Isometric Finger Device for Assessment and Training of Force Coordination Using Virtual Reality

[+] Author and Article Information
Gregorij Kurillo1

Laboratory of Robotics and Biomedical Engineering, Faculty of Electrical Engineering,  University of Ljubljana, Tržaška 25, 1000 Ljubljana, Sloveniagregorij@eecs.berkeley.edu

Matjaž Mihelj, Marko Munih, Tadej Bajd

Laboratory of Robotics and Biomedical Engineering, Faculty of Electrical Engineering,  University of Ljubljana, Tržaška 25, 1000 Ljubljana, Slovenia

1

Corresponding author. Present address: Department of Electrical Engineering and Computer Science, University of California Berkeley, Hearst Memorial Mining Building #475, Berkeley, CA 94720.

J. Med. Devices 1(4), 279-282 (Aug 14, 2007) (4 pages) doi:10.1115/1.2812428 History: Received November 21, 2006; Revised August 14, 2007

Grasping of stroke patients is often affected by improper coactivation of muscles controlling the fingers. The restoration of hand function therefore represents an important goal in rehabilitation. Quantitative data on coordination between fingers can be helpful for the assessment of therapy effectiveness. We have designed a novel isometric finger device to assess three-dimensional forces applied by the thumb, index, and middle finger. The device was used in connection with a simple virtual reality task where the patient had to open a safe by sequentially rotating a knob using the isometric finger input. The presented virtual reality application was evaluated in a group of healthy subjects and a chronic stroke patient to obtain preliminary performance results. We analyzed the coordination of fingertip forces between the thumb and opposing fingers. Pearson correlation coefficient was determined to assess the coordination of force in each direction. In healthy subjects, the analysis of the fingertip forces showed precise coordination of force between the fingers to control a virtual object. The performance of the stroke patient was considerably lower due to reduced muscle control and presence of strong spasticity. The results showed use of excessive force in both hands and lower coordination of force between the fingers as compared to the healthy subjects. The proposed virtual reality system is considered as a complementary method to the existing methods used in physical and occupational therapy. Specific virtual reality tasks could be designed to train coordination of force between the affected fingers.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

Grahic Jump Location
Figure 4

The average correlation coefficients as obtained in the group of healthy subjects (light gray) and the stroke patient (dark gray). Mean values and standard deviation of the correlation coefficients between the forces of the thumb (T), index (I), and middle (M) finger are shown for the normal (z) and two tangential directions (x and y). Higher coordination coefficient indicates more synchronized activation of the fingers to control the output force ( *P<0.05, t-test).

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Figure 3

Thumb force outputs of a healthy subject (a) and stroke patient (b) during the opening of the virtual safe. Lateral force (Fx) was applied to rotate the knob in each direction while the normal force (Fz) was used to grasp the knob.

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Figure 2

Rotation of the safe knob during the task performance of a healthy subject. The dotted reference line represents the required orientation of the knob for a particular safe combination (a). The average time (with standard deviation) required to open the virtual safe as assessed in the group of ten healthy subjects and stroke patient during four training sessions (b).

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Figure 1

Isometric finger device was designed to simultaneously measure forces and torques applied by the thumb, index, and middle finger (a). The subjects used the isometric finger device to open a virtual safe by rotating the knob according to the presented combination code (b).

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