Small steps for paralyzed man,  giant leaps for treating spinal cord injuries:

Effect of epidural stimulation of the lumbosacral spinal cord on voluntary movement, standing, and assisted stepping after motor complete paraplegia: a case study

Susan Harkema, Yury Gerasimenko, Jonathan Hodes, Joel Burdick, Claudia Angeli, Yangsheng Chen, Christie Ferreira, Andrea Willhite, Enrico Rejc, Robert Grossman and  Reggie Edgerton

The Lancet, doi:10.1016/S0140-6736(11)60547-3; The full article in the Lancet is also available online

A Review by Nick Donaldson

In recent years, Dimitrievic and his colleagues have demonstrated to us at the Vienna meetings how multi-joint leg movements can be produced in patients with SCI by tonic stimulation of the posterior spinal cord at the lumbo-sacral enlargement. Harkema et al. describe how they combined this technique with standing- and treadmill-training. Their hypothesis was that tonic stimulation could bring the spinal circuits to a state where sensory inputs would suffice to produce standing and stepping. Treadmill training alone does not have beneficial training effect in completely paralysed patients.

Their single ASIA B patient (C7-T1) had over 2 years of treadmill- and standing-training (170 sessions) before stimulation was started without any improvement as assessed by EMG response to afferent input. A 16-electrode epidural array was then implanted with a stimulator that allowed tonic stimulation between selected groups of these electrodes. Standing was enabled using caudal (L5-S1) electrodes at 15Hz, EMG being modulated by the degree of body weight support (BWS) and the inclination of the body. After 80 stimulation sessions, the subject could stand without BWS for up to 4.25 minutes but there were bouts of clonus (see video at^[1] ). With higher frequency, at 50% BWS and alternating load on the feet, induced by the therapists, stepping was produced with the appropriate EMG activity. Stimulation was only applied in the laboratory.

Thus in this one subject, the hypothesis was true, epidural stimulation enabled afferent-driven standing and stepping. However, the researchers also found that supraspinal control began to return: the subject can voluntarily flex his legs and extend his toes during stimulation. Other functions recovered, that do not require concomitant stimulation: sexual, bladder and temperature regulation.

A carry-over effect has been observed in other single-subject studies in which there was a lot of muscle stimulation over a long period^[2],[3]. In this case, for life after the project, the carry-over seems likely to be at least as valuable to the subject as the exercise that has been enabled by the stimulation.

I note 4 other interesting points about this approach.

(a)    There is only tonic stimulation so unlike FES-walking, there is no artificial controller; control must be from spinal cord and brain. This may be a paradigm shift in rehabilitation after SCI but perhaps at present we should bear in mind that there are 2 or 3 therapists brains involved as well, perhaps, as that of the subject.

(b)   I see no indication in the data presented that independent walking will be possible only with this method.

(c)    The implant is relatively simple compared to implants for FES-walking and does not have many cables with the associated unreliability.

(d)   A chronic implant was used with intense (expensive) therapy and the greatest outcome benefit was therapeutic. Might implants for a limited period of therapy be acceptable and cost-effective?

I think that this is a very important paper for the FES community that challenges our conventional ideas and methods.

Nick Donaldson

Implanted Devices Group
UniversityCollege London