IFESS 20001

Abstract

A quantitative hand grasp and release test was developed to assess function following the implantation of an upper extremity neuroprosthesis in persons with C5 and C6 level spinal cord injury. The Grasp and Release Test (GRT) consists of six different objects, varying in size and weight, which the participant is required to acquire, move and release to a designated target area. Grasp strength is measured at the start of the test. Data from five participants has been previously published. To date, more than 20 neuroprosthesis users have participated in this Grasp and Release Test (GRT). The test was administered prior to implantation and at several intervals following implantation. Results show that the implanted neuroprosthesis provides participants with increased grasp strength, the ability to acquire and release more objects, and move objects more quickly. Grasp strength and the ability to acquire and release objects has remained stable over time.

Introduction/Background

Over the past 15 years, nearly 30 persons with C5 or C6 tetraplegia^{1 (}O/Cu:0-2)²have been implemented with one of two types of an implanted upper extremity neuroprosthesis via the Cleveland FES Center. Both neuroprostheses were developed by researchers at Case Western Reserve University and the Cleveland VA Medical Center^{3, 4, 5}. The conventional hand neuroprosthesis is currently marketed as the Freehand System^a. More than 100 individuals with mid-cervical level spinal cord injury have been implanted with this commercial system internationally. Users of a new neuroprosthesis currently being researched at this center also participated in this study. This system provides additional channels of stimulation and an implanted joint angle transducer placed in the wrist to control opening and closing of the hand⁶. Currently, four individuals with tetraplegia have been implanted with this system.

The Grasp and Release Test (GRT) was developed to measure changes in hand function following the implantation of an upper extremity neuroprosthesis. The test was developed due to the absence of an existing test that was appropriate to measure changes in hand function for this population⁷. Data from five participants has previously been published⁷. The objectives of this study are to 1) determine the changes in hand strength with and without a neuroprosthesis 2) determine the ability to acquire and release objects with and without a neuroprosthesis 3) to determine the stability of strength and test performance over time with a neuroprosthesis. Twenty-three neuroprosthesis users from the Cleveland FES Center participated in this study.

Methods

Test Description: At the start of the test, grasp strength was measured with and without the neuroprosthesis using a modified pinch meter. The meter was modified to better accommodate a tetraplegic hand by providing a larger base upon which to pinch. Three trials of grasping were tested for each of the following grasp patterns: lateral, palmar and five finger.

Following grasp measurements, a pre-test was performed. The pre-test required manipulation of six objects, three with lateral prehension (peg, fork, paper weight) and three with palmar prehension (block, can, video tape). The participant was encouraged to acquire each object from one side of the test board and release in on the opposite side of the board. The participant was encouraged to do this for each object with the neuroprosthesis turned on and off. If the participant had difficulty manipulating an object, he/she was encouraged to practice until they could manipulate the object successfully or determine that they could not manipulate the object after offering their best effort. Scoring for the pre-test was pass or fail.

The pre-test was followed by the main test. The main test consisted of three thirty-second trials during which the participant was instructed to move the object from its start position to the targeted release area on the other side of the test board. The exception to this is for the fork, in which the participant was instructed to grasp the handle, depress the piston past the indicator line, release the handle and place his/her hand back at the starting position repetitively throughout the trial. The number of successful completions and errors were counted for each trial. The objects that were successfully passed in the pre-test were included in the main test.

Participants: Twenty-three neuroprosthesis users participated in the study. Participant demographics are shown in Table I. Twenty-one participants were implemented with the Freehand System and two of the participants were implemented with the research neuroprosthesis.

Results

Grasp Strength: The results of grasp strength measured with and without the neuroprosthesis are shown in Figure I. Grasp strength increased with the neuroprosthesis.

Object Manipulation: The ability for participants to manipulate objects with and without the neurorposthesis is shown in Figure II. Many of the participants were able to manipulate the smaller, lighter objects without the neuroprosthesis turned on. However, as the objects became heavier or larger, fewer participants were able to pass the objects without the neuroprosthesis. Nearly all participants were able to pass all of the objects with the neuroprosthesis turned on.

Additional data including the number of completions achieved during trials as well as stability of grasp strength and test performance over time is currently being analyzed. Initial data analysis reveals that C5 participants’ can manipulate objects more quickly with the neuroprosthesis. Participants with a C6 injury can manipulate the larger or more difficult object more easily with the neuroprosthesis, however, they are able to manipulate the smaller lighter objects more quickly without the neuroprosthesis by using a tenodesis grasp. Grasp strength stays stable over time.

Discussion/Conclusions

The GRT is useful for determining the effects an implanted neuroprosthesis has on grasp strength and the ability to manipulate objects. Participants have shown increased grasp strength and better ability to manipulate objects with the neuroprosthesis turned on.

As a larger number of participants are implemented with the research neuroprosthesis, comparisons in strength and the ability to manipulate objects will be made to users of the Freehand system.

References

1. American Spinal Injury Association: International Standards for Neurological and Functional Classification of Spinal Cord Injury. Chicago, 1996

2. McDowell CL, Moberg EA, House JH. The second international conference on surgical rehabilitation of the upper limb in tetraplegia (quadriplegia). J Hand Surg 1986;11A:604-8.

3. Keith MW, Peckham PH, Thrope GB, Stroh KC, Smith B, Buckett JR, et al. Implantable functional neuromuscular stimulation in the tetraplegic hand. J of Hand Surg 1989; 14A:524-30.

4. Peckham PH, Keith W, Freehafer AA. Restoration of functional control by electrical stimulation in the upper extremity of the quadriplegic patient. J Bone Joint Surg 1988; 70A:144-8.

5. Kilgore KL, Peckham PH, Keith MW, Thrope GB, Wuolle KS, Bryden AB, Hart RL. An implanted upper-extremity neuroprosthesis: Follow-up of five patients. J Bone Joint Surg 1997;79A:533-41.

6. Smith B, Tang Z, Johnson MW, Pourmehdi S, Gazdik MM, Buckett JR, Peckham PH. An externally powered, multichannel, implantable stimulator-telemeter for control of paralyzed muscle. IEEE Trans Biomed Eng 1998;45:463-75.

7. Wuolle KS, VanDoren CL, Thrope GB, Keith MW, Peckham PH. Development of a quantitative hand grasp and release test for patients with tetraplegia using a hand neuroprosthesis. J of Hand Surg 1994; 19A:209-218.

a. NeuroControl Corporation, 8333 Rockside road, Valley View, Ohio 44125.

Acknowledgments: This study was supported by the Department of Veterans Affairs Rehabilitation Research and Development Service.