Northwestern University Feinberg School of Medicine

Northwestern University Prosthetics-Orthotics Center

Assessing Performance Claims for Multi-Degree-of-Freedom Articulated Hands

Principal Investigator: Steven A. Gard, PhD

Co-Investigators: Edward Grahn, BSME; Matthew Major, PhD; Rebecca Stine, MS; Stefania Fatone, PhD

Project Director: Craig Heckathorne, MS

Funded by: National Institute on Disability and Rehabilitation Research (NIDRR)

Status: Completed

Introduction

Before 2007, all commercially available electric-powered prosthetic hands utilized a single-degree-of-freedom (single-DOF) actuator design to open and close the fingers and thumb. The digits were configured in the pattern of palmar prehension with the distal palmar pad of the thumb opposing the distal palmar pads of the index and middle fingers, the most common grasp pattern of the human hand. This arrangement also offered cylindrical prehension for wider objects and hook prehension for rods or handles. Although this type of hand has been useful for many activities, designers of prosthetic hands have long sought to develop articulated hands with multiple degrees-of-freedom (multi-DOF) that are able to assume a greater variety of grasp patterns. It was believed that such hands would, in form and action, be more akin to the physiological hand and would, as a consequence, improve manipulative function.

Many designs have been proposed for articulated prosthetic hands. The first electric-powered articulated hand to reach commercialization was the i-limb hand by Touch Bionics (Livingston, United Kingdom), introduced in 2007. The i-limb hand has a set of individual motorized fingers and thumb that can conform to the shape of an object being held. The thumb can be positioned so that it opposes the index and middle fingers (palmar prehension or tripod grip) or the lateral surface of the index finger (lateral prehension or key grip). Positioning of the thumb is done manually for the original i-limb, the i-limb pulse, and the i-limb ultra hands, and is positioned with a motor for the i-limb ultra revolution hand. Users of the i-limb hand comment on its "natural movement", its ability to hold securely a greater variety of objects, reduced mental loading when grasping an object, reduced compensatory arm movements to orient the hand for grasping, everyday activities being "much easier", and being able to hold objects "in the normal way". These claims, based on personal user assessment, are compelling but have not been tested with controlled performance studies.

Specific Objectives

We are conducting two quantitative studies to investigate the qualitative claims made for the Touch Bionics' hands. The first study will determine if a quantitative difference exists in the ability of users of single-DOF and of multi-DOF prosthetic hands when handling a variety of objects in different manipulative tasks.

This study includes three subject groups. The first two groups are persons with unilateral transradial amputations who customarily use a myoelectrically-controlled electric-powered hand. One group will be users of single-DOF hands; the second group will be users of the multi-DOF i-limb hand. The third group, a control group, will be persons with intact upper-limbs.

Manipulative performance will be examined in three ways. The first method will use a standardized, self-administered, functional performance questionnaire involving self-care and upper-limb daily living skills. The second method will have the subjects perform a set of timed pick-and-place and activity tasks using standardized objects while their arm and body positions and movements are tracked and recorded by a motion analysis system. The third method will have the subjects perform a common daily activity at their own pace, again with motion tracking of arm and body movements. Results from the three methods will be compared to determine if significant performance differences exist between users of the two types of electric hands and between each of these groups and the control group.

The second study will compare the grip efficiency, calculated as the ratio of the force required to dislodge a grasped object to the grip force applied by the prosthetic hand, for a single-DOF hand and the i-limb hand using a variety of simple, geometrically shaped objects.

Clinical Implications

Quantitative evidence to support a functional benefit of an articulated (multi-DOF) hand over a single-DOF hand could be used to justify prescribing an articulated hand, even if the hand were more expensive and/or less durable than a single-DOF hand. Such evidence could also encourage further development of articulated hands. Furthermore, an independent, objective study of prosthetic hand function offers clinicians additional knowledge in exercising their professional judgment during clinical assessment and decision making.

Related Presentations and Publications

Heckathorne C. Design and Evaluation of Multi-Articulated Prosthetic Hands. Midwest Chapter American Academy of Orthotists and Prosthetists (AAOP) Annual Fall Session, September 18, 2010, Lake Geneva, WI.

Heckathorne C, Stine R. Using Motion Analysis to Augment Upper-limb Prosthetics Outcome Measures. MEC '11 Symposium; August 17-19, 2011, University of New Brunswick, Fredricton, Canada.

Major M, Heckathorne C, Stine R, Fatone S, Gard S (2013) Assessing the effects of myoelectric prosthetic hand use on upper body dynamics: A preliminary study. Virginia Orthotic & Prosthetic Association Annual Meeting, October 5, Fairfax, VA.

Heckathorne C, Stine R, Major M, Gard S, Fatone S. (2014) Investigating the Effects of Prosthetic Hand Design on Performance. 40th American Academy of Orthotists and Prosthetists Annual Meeting & Scientific Symposium, February 26-March 1, Chicago, Illinois.

Major M, Stine R, Heckathorne C, Fatone S, Gard S. (2014) Upper Body Kinematic Range-of-Motion and Variability of Transradial Prosthesis Users Performing Goal-Oriented Tasks. World Congress of Biomechanics, July 6-11, Boston, MA.

Major MJ, Stine R, Heckathorne C, Fatone S, Gard SA. (2014) Comparison of range-of-motion and variability in upper body movements between transradial prosthesis users and able-bodied controls when executing goal-oriented tasks. Journal of NeuroEngineering and Rehabilitation, 11:132.