DERMATOME ELECTRICAL STIMULATION AS A THERAPEUTIC AMBULATORY AID FOR INCOMPLETE SCI PATIENTS

T. Bajd, M. Munih, R. Šavrin*, H. Benko*, and I. Cikajlo

Faculty of Electrical Engineering, University of Ljubljana, Slovenia

*Rehabilitation Institute, Ljubljana, Slovenia

SUMMARY

Electrical stimulation of the L-3,4 dermatome during treadmill walking is proposed as a gait training modality in incomplete spinal cord injured (SCI) patients. The dermatome stimulation proved to be efficient in diminishing the extensor tone occuring after loading of the paralyzed limb during the stance phase of walking and resulting in improved flexion of the leg during the swing phase.

STATE OF THE ART

In the last decades more incomplete than complete SCI patients are arriving to the spinal units. One of the primary goals of the rehabilitative program for the incompletely paralyzed subjects is not only returning them into standing position, but also restoring their walking patterns. There are several gait training modalities available for this group of patients. In Table 1 they are divided into the methods based on mechanical activation or electrical stimulation of the partially paralyzed lower extremities. Some of these approaches are only provoking passive movement of the leg, while others are eliciting reflex responses.

Table 1. Gait training in partially paralyzed patients

It is our belief that the approaches which are merely providing the movement of the leg are less efficient in re-learning of patient's walking. Robot manipulators combined with treadmill are used to lift the leg and bring the foot forward. In this case only the afferent input from the joint receptors may promote the gait re-learning process. Similar movements can be accomplished by active exoskeleton systems. Gait pattern can be restored in paralyzed persons also by surface or percutaneous multichannel electrical stimulation. Strong electrical stimuli delivered to the efferent nerves may represent unwanted noise in the afferent nerves, thus hindering the re-learning process.

The gait training modalities eliciting reflex responses result in more complex and natural like movements which are provoking afferent signals in joints, tendons, and muscles. Treadmill is producing hip extension at the end of the stance phase which is inducing reflex hip flexion and thus initiating the swing phase of walking /1/. A powerful motor and gear system attached to a mechanical ankle joint orthosis by means of flexible bowden cables, can elicit stretch reflexes by displacing rapidly the ankle joint /2/. Vibration of muscles and tendons activates muscle spindle afferents and produces illusory changes in joint position /3/. Illusion of the altered position may play important role in gait training. It has been demonstrated already in 1973 /4/ that electrical pulses applied to the sural or tibial nerves result in reflex hip and knee flexion with a simultaneous reflex ankle dorsiflexion. The swing phase obtained by eliciting a synergistic flexion response through electrical stimulation of the common peroneal nerve was extensively used by our group /5/. The spinal cord stimulation has a predominantly afferent influence /6/. Due to this stimulation the supraspinal structures exert their influence through the descending pathways and segmental reflexes, and thus at least partially restore the brain control over the locomotor system. In this paper we are proposing the dermatome stimulation combined with treadmill walking as a modality for gait training in incomplete SCI persons /7/.

METHODS

The swing phase of walking can be influenced through cutaneous stimulation of the selected dermatomes. In the investigation a 63y. old patient with C 2-6 spinal cord lesion resulting from an accident has been selected. The electrodes were placed over the L-3,4 dermatome, one medially below the knee and the other laterally above it, with the aim to decrease the extensor spasticity of the knee extensors, innervated from the same spinal cord level as the dermatome. Schematic representation of electrodes positioning is shown in Figure 1. A stimulation frequency of 100 Hz and a pulse duration of 0.3 ms were used without interruption during the gait cycles. The electrical stimulation was not causing any muscle contraction. It is our belief that the sensory electrical stimulation was delivered predominantly through the large diameter afferent fibers.

Fig. 1 Positioning of the surface electrodes over the L-3,4 dermatome.

Fig. 2. Record of an incomplete SCI patient’s walking without (upper row) and with the dermatome electrical stimulation (lower row).

RESULTS

Strong extensor spasticity is often observed in the lower extremities of the incomplete SCI patients. After loading the paralyzed limb during the stance phase of walking, the patients have difficulty to break this extension tone and cannot initiate a step. The stimulation of the L-3,4 dermatome proved to be efficient in diminishing this extensor activity. Hip and knee flexion and ankle dorsiflexion were significantly increased during the swing phase of walking. Also, the eversion of the foot was noticeably improved when delivering the dermatome stimulation. The upper series of the photographs in Figure 2 belongs to walking without stimulation. The lower photographs show improved swing phase of walking during L-3,4 dermatome stimulation. The dermatome stimulation proved to be specially efficient when combined with treadmill walking.

DISCUSSION

In spite of several decades of investigations of FES for lower extremities we cannot claim that FES of lower limbs is widely used in clinical environment. The FES synthesis of walking requires complex multijoint movements which further require large number of surface or implanted electrodes together with special algorthms providing coordination of many channels of electrical stimulation. It is our belief that only simple FES systems are perspective from the clinical point of view. Electrical stimulation of spinal neural circuits, rather than direct activation of motoneurons, will simplify generation of complex motor behaviours /8/. Electrical stimulation of the dermatomes, described in this paper, is just one possible access to the spinal neural circuitry from the periphery.

REFERENCES

/1/ Wernig A., Müller S., Laufband locomotion with body weight support improved walking in persons with severe spinal cord injuries, Paraplegia, Vol. 30, 1992, 229-238.

/2/ Andersen J.B., Sinkjaer T., An actuator system for investigating electrophysiological and biomechanical features around the human ankle joint during gait, IEEE Trans. Rehab. Eng., Vol. 3, 1995, 299-306.

/3/ Gandevia S.C., Kinesthesia: Roles for afferent signals and motor commands, In: Rowell L.B. and Shepherd J.T. Eds. Handbook of Physiology, Oxford University Press, 1996, 128-172.

/4/ Liberson W.T., Functional electrical stimulation in paraplegics and »Reflex Walking«, Arch. Phys. Med. Rehabil., Vol. 54, 1973, 588.

/5/ Bajd T., Kralj A., Turk R., Benko H., Šega J., The use of a four-channel electrical stimulator as an ambulatory aid for paraplegic patients, Phys. Ther., Vol. 63, 1983, 1116-1120.

/6/ Cook A.W., Taylor J.K., Nidzgorski F., Functional stimulation of spinal cord in multiple sclerosis, J. Med. Eng. Technol., Vol. 3, 1979, 18-23.

/7/ Bajd T., Gregorič M., Vodovnik L., Benko H., Electrical stimulation in treating spasticity resulting from spinal cord injury, Arch. Phys. Med. Rehabil., Vol. 66, 1985, 515-517.

/8/ Grill W.M., Electrical activation of spinal circuits: Application to motor-system neural prostheses, Neuromodulation, Vol. 3, 2000, 97-106.

AUTHOR'S ADDRESS

Prof. Dr. Tadej Bajd,

Faculty of Electrical Engineering e-mail: tadej.bajd@fe.uni-lj.si

University of Ljubljana home page: www.fe.uni-lj.si

1000 Ljubljana, Tržaška 25, Slovenia