IEEE TRANSACTIONS ON REHABILITATION ENGINEERING, VOL. 7, NO. 1, MARCH 1999
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Communications The Effect of Wrist Angle on Electrically Evoked Hand Opening in Patients with Spastic Hemiplegia
TABLE I SUBJECT PROFILES
T. Cameron, K. McDonald, L. Anderson, and A. Prochazka
Abstract—This paper studied the effect of wrist angle on the amount of hand opening achieved by electrical stimulation in people with spastic hemiplegia. With their forearm in pronation, subjects were asked to relax while their affected wrist was passively moved in steps of about 15 from full flexion into extension. Trains of stimuli were applied to the long finger extensor muscles through surface electrodes on the forearm. At each wrist position stimulation was turned on for a few seconds until hand opening equilibrated. Wrist angle and fingertip positions were recorded using a three-dimensional (3-D) motion analysis system. Maximal displacements between thumbtip and each fingertip occurred when the wrist was fully flexed. As the wrist was extended, hand aperture achieved by electrical stimulation progressively declined, reaching zero at 40 of wrist extension. We conclude that electrical stimulation can significantly increase the grasp aperture of the hemiplegic hand, but this is strongly dependent on wrist posture and accompanying voluntary effort. Index Terms— Functional electrical stimulation (FES), hemiplegia, stroke.
I. INTRODUCTION
(a)
A common problem after stroke is hyperreflexia (spasticity) of the hand flexors and a weakness or paralysis of the extensors, resulting in involuntary formation of a fist. This leads to difficulties in grasping and releasing objects. Functional electrical stimulation (FES) is sometimes used by therapists to improve function and reduce spasticity in the paralyzed hand [3]. Recently, portable FES devices have been developed for quadriplegic [1], [4], [8], [10], [11] and hemiplegic people [7], [9]. When possible, C6-7 quadriparetic subjects are taught to generate residual hand function by using “tenodesis grasp,” whereby voluntary wrist extension stretches the long finger flexors, pulling the fingers into flexion. The hand is opened by voluntarily flexing the wrist which passively unloads the flexors and stretches the extensors, causing the fingers to extend and thus release the grasp [3]. This is usually not possible in hemiparetic subjects because flexor spasticity keeps the hand closed even when the wrist is quite flexed. The purpose of the present study was to examine the relationship between wrist angle and FES-evoked hand opening. II. METHODS Five subjects with spastic paresis due to cerebrovascular accident (CVA) of at least one year’s standing participated in the study with informed consent according to procedures approved by the University of Alberta Human Ethics Committee and laid out in the Declaration of Helsinki. Table I summarizes the clinical characteristics of the patients who all had spasticity in their finger flexor muscles on the affected side. Manuscript received June 24, 1997; revised May 26, 1998. This work was supported by the Alberta Heritage Foundation for Medical Research and the Neuroscience Network. The authors are with the Division of Neuroscience, University of Alberta, Edmonton, Alta. T6G 2S2 Canada. Publisher Item Identifier S 1063-6528(99)02227-2.
(b)
Fig. 1. Tracing of a hemiplegic hand with active electrode (cathode) on dorsal surface of forearm, indifferent electrode (anode) on ventral surface close to wrist crease and motion sensors on fingertips. Wrist at 30 flexion. (a) before stimulation and (b) during stimulation.
Motor points were localized using a moist-pad cathodic search electrode through which trains of stimuli (biphasic pulses 150 s, 30/s, 35 Amp) were applied, the anode being an adhesive gel electrode (Chattanooga Corp., 10 cm 2 5 cm) attached to the ventral forearm just proximal to the wrist. The optimal motor point for hand opening was the site that caused the greatest finger extension and thumb abduction/extension with wrist slightly flexed (usually over extensor digitorum comminus (EDC)). An adhesive gel electrode (5 cm 2 4.5 cm) was attached at this site. One of the 5 subjects required a second active electrode over the dorsal surface of the distal forearm [over extensor pollicis brevis (EPB) and abductor pollicis longus (APL)] to produce adequate thumb abduction. Wrist angle and fingertip positions were recorded using a threedimensional (3-D) motion analysis system (6D-Research).1 Six sensors were attached as follows: 1) dorsal surface of the lower forearm just proximal to the wrist crease, 2) midpoint of third metacarpal segment, 3–5) distal phalanges of digits 1–3, 6) distal phalanx of digit 4 or 5, whichever had the smaller displacement from the thumbtip during stimulation. Grasp aperture was defined as the minimum of the 4 distances measured between thumbtip and the four fingertips. Subjects were asked to relax as much as possible and with the wrist slightly flexed, pulse train amplitude was set to produce maximal finger aperture without causing discomfort (typically 40–45 mAmp). The hand was moved by the experimenter in steps of 15 from full flexion into full extension. Stimulation was applied for a few seconds 1 6D-Research
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IEEE TRANSACTIONS ON REHABILITATION ENGINEERING, VOL. 7, NO. 1, MARCH 1999
(a)
(b)
(c) Fig. 2. Hand aperture versus wrist angle; pooled data from all five subjects. Open circles: distances between digits without stimulation, filled circles: distances between tips of digits during hand-opening stimulation. (a) thumb to forefinger (digit 1 to digit 2: D1-D2), (b) thumb to digit 3, and (c) thumb to digit 4 or 5, whichever distance was smaller during stimulation. Thick lines: second-order linear regression curves, thin lines: 95th percentile confidence intervals.
at each position until hand opening stabilized. Wrist angle and motion sensor data were recorded. The distances between the thumbtip and each fingertip were subsequently measured and plotted against wrist angle. Second-order regression lines were fitted to the individual and to the pooled data. III. RESULTS All five subjects had difficulty relaxing their affected hand and none could open the hand voluntarily. FES evoked useful hand opening in all subjects. Fig. 1 shows the hand of subject EC, before (a) and during (b) FES. The wrist was passively moved through six angles. FES was applied for a few seconds at each angle. Achieved hand aperture was related to wrist angle in all patients. Fig. 2 shows the mean distances between thumbtip and the tips of digits 2, 3, and 4 in these trials. Maximal aperture occurred at maximal wrist flexion (+40 ). Minimal aperture occurred at maximal wrist extension (040 ). When the wrist was extended beyond 40 , FES did not increase aperture. Wrist flexion allowed FES to increase aperture by as much as 6 cm over that when the wrist was extended. Qualitatively similar results were obtained with the hand half-supinated, a posture appropriate for grasping and lifting an object such as a pop can. IV. DISCUSSION
AND
CONCLUSION
Our results show that FES can significantly increase the grasp aperture of the hemiplegic hand, but that this strongly depends on
wrist posture. A single active surface electrode applied over the extrinsic finger extensor muscles was sufficient to produce full hand opening in 4/5 subjects. A second electrode was required to elicit thumb extension in the remaining subject. Maximal hand opening occurred when the patients were fully relaxed with wrists in the fully flexed position. Previous studies have also found FES to be a useful technique to restore opening of the hemiparetic hand. Hines et al. [2] reported that stimulation of both EDC and the ulnar nerve were necessary to achieve adequate finger extension. EDC stimulation alone produced full extension in the metacarpophalageal (MP) joints but often caused flexion in the interphalangeal (IP) joints. In our study, we obtained full MP and IP extension in 4/5 subjects with a single active electrode. The remaining subject had extremely tight IP joints that could not be extended even with high-amplitude stimulation. Stimulation of EPB and APL with a separate electrode provided the necessary thumb extension/abduction in this case. One limitation of FES is the requirement that subjects remain relaxed in order to achieve maximal hand opening [2]. This can be difficult when FES is used in a functional task, such as reaching to grasp an object. We found that the effort associated with flexing the fingers to hold an object reduced the efficacy of FES to reopen the hand. This is related to the abnormally long time needed to relax the fingers after flexion in hemiplegic people. Bringing the wrist into full flexion often relaxed the affected finger muscles enough to allow extensor FES to open the hand. Resting the forearm on a supporting surface such as a table-top or arm-rest was also effective. These
IEEE TRANSACTIONS ON REHABILITATION ENGINEERING, VOL. 7, NO. 1, MARCH 1999
and other strategies are used by hemiplegic people testing a new hand-opening FES device, the “Impact Cuff” [9] in tasks of daily life. Our results suggest that FES of the hemiparetic hand in many cases produces sufficient opening to enhance the performance of activities of daily living. Fig. 2 shows that with the wrist flexed, FES increased the grasp aperture by about 5 or 6 cm, enough to grasp an object like a pop can, leaving the nonaffected hand free to manipulate the object or to do other tasks. An appropriate FES device need not be complicated, as we were able to achieve adequate opening with one active surface electrode in four patients and two electrodes in the remaining subject. Keeping the wrist in a flexed position during electrical stimulation of the extensor muscles greatly increases the aperture of the hand, while extending the wrist produces increased finger flexion during grasp. Hines et al. [2] have suggested that flexor stimulation to produce grasp without voluntary effort would allow stimulation of the finger extensors to produce its maximal hand-opening effect. In some subjects this may be necessary but by taking advantage of wrist posture, flexor stimulation may be unnecessary in many cases.
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Knee Elasticity Influenced by Joint Angle and Perturbation Intensity Changfeng Tai and Charles J. Robinson
Abstract— The responses of the human knee joint system to small rotational displacements were studied in the horizontal plane to eliminate the effect of gravity. Band-limited noise was used to produce up to ±3 angular perturbations to the knee joint. Under these restricted conditions, the knee joint system could be described by a linear, second-order model with the assumption that the mechanical properties of the knee were constant over these small displacements. The elasticity about the knee was influenced not only by the static joint angle but also by the perturbation intensity. Realistic models of the knee joint system should be modeled by a position-dependent, nonlinear system to remain valid over a large range of rotation. Index Terms—Biomechanics, knee elasticity, knee joint, linear model, perturbation, stiffness.
I. INTRODUCTION REFERENCES [1] Y. Handa, T. Handa, Y. Nakatsuchi, Y. Tagi, and N. Hoshimiya, “A voice-controlled functional electrical stimulation system for the paralyzed hand,” Iyodenshi to Seitai Kogaku, vol. 23, pp. 292–298, 1985. [2] A. E. Hines, P. E. Crago, and C. Billian, “Hand opening by electrical stimulation in patients with spastic hemiplegia,” IEEE Trans Rehab. Eng., vol. 3, pp. 193–205, June 1995. [3] L. D. Hollar, “Spinal cord injury,” in Occupational Therapy for Physcial Dysfunction, C.A. Trombly, Ed. Baltimore, MD: Williams and Wilkins, 1995, ch. 39, pp. 795–813. [4] M. W. Keith, P. H. Pechham, G. B. Thorpe, K. C. Stroh, B. Smith, J. R. Buckett, K. L. Kilgore, and J. W. Jatch, “Implantable functional neuromuscular stimulation in the tetraplegic hand,” J. Hand Surg., vol. 14, pp. 524–530, May 1989. [5] G. H. Kraft, S. S. Fitts, and M. C. Hammond, “Techniques to improve function of the arm and hand in chronic hemiplegia,” Arch. Phys. Med. Rehab., vol. 73, pp. 220–227, Mar. 1992. [6] R. Merletti, R. Acimovic, S. Grobelnik, and G. Cvilak, “Electrophysiological orthosis for the upper extremity in hemiplegia: Feasibility study,” Arch. Phys. Med. Rehab., vol. 56, pp. 507–513, Dec. 1975. [7] R. H. Nathan, “Device for generating hand function,” U.S. Patent 5 330 516, July 1994, pp. 1–10. [8] A. Prochazka, M. Gauthier, M. Wieler, and Z. Kenwell, “The bionic glove: An electrical stimulator garment that provides controlled grasp and hand opening in quadriplegia,” Arch. Phys. Med. Rehab., vol. 78, pp. 608–614, June 1997. [9] A. Prochazka, “Garment having controller that is activated by mechanical impact,” Canadian Patent Office, PCT Patent Filing, Oct. 1997, pp. 1–19. [10] S. Rebersek and L. Vodvnik, “Proportionally controlled functional electrical stimulation of hand,” Arch. Phys. Med. Rehab., vol. 54, pp. 378–382, Aug. 1973. [11] D. Rudel, T. Bajd, A. Kralj, and H. Benko, “Surface functional electrical stimulation of the hand in quadriplegics,” in Proc. 5th Annu. Conf. Rehab. Eng., 1982, p. 59.
Linear methods have been applied to study the responses to mechanical perturbation of a wide variety of joints, including the ankle [1], [2], wrist [3], and elbow [4]. A common finding has been that linear models provide an excellent description of joint dynamics provided that conditions are maintained approximately constant throughout the experiment. But only a few studies have focused on the knee, especially using a linear second-order model. Most of the studies on the human knee have used complex analytic models [5], whose many parameters are identified with difficulty. Mansour et al. [16] found that the knee stiffness changes nonlinearly with joint angle in a large range of motion. To describe the knee dynamics in a large range of motion, Franken et al. [6] added a nonlinear exponential term to the second-order model of the knee joint instead of the elasticity parameter. Vodovnik [7] and Lin et al. [8] also found that the knee elasticity was influenced by the range of motion in the studies of pendular movement of the lower leg. Weiss et al. [9] found that the elasticity of the ankle joint varied with angular position. Kearney and Hunter [2] had previously shown that the elasticity of the ankle joint was influenced by perturbation intensity. A priori then, one might expect the physiological and mechanical properties of the knee joint to depend upon the joint angle. But the quantitative answer to this question is important and helpful in the development of a knee model describing the accurate relationship between knee joint torque and position. This knowledge might prove useful in the design of neural prostheses [8] and their Manuscript received February 9, 1998; revised April 6, 1998 and September 1, 1998. This work was supported in part by the Chinese State Education Commission, the University of Pittsburgh, and the VA Pittsburgh Health Care System. This work was performed at the SLIP-FALLS Laboratory at the Pittsburgh Veterans Affairs HealthCare System, Highland Drive location. The review and acceptance process for this manuscript was handled in its entirety by Associate Editor R. B. Stein. C. Tai is with the Department of Rehabilitation Science and Technology, University of Pittsburgh, Pittsburgh, PA 15260 USA. He is also with the Rehabilitative Neuroscience Laboratory, VA Pittsburgh HealthCare System, Pittsburgh, PA 15206 USA, and the Biomedical Engineering Institute, Xi’an Jiaotong University, Xi’an, 710049 China. C. J. Robinson is with the Department of Rehabilitation Science and Technology, University of Pittsburgh, Pittsburgh, PA 15260 USA (e-mail:
[email protected]). Publisher Item Identifier S 1063-6528(99)01169-6.
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