Lower-Limb Neuroprostheses: Restoring Walking after Spinal Cord Injury

Introduction

Spinal Cord Injury (SCI) is a devastating neural dysfunction affecting a large population worldwide. Though the exact prevalence of SCI is unknown, according to recent statistics, it is estimated that the number of injuries between 236 and 1009 per million (Lee et al., 2013). Considering the current world population at about 7 billion, the total SCI number ranges from 1.65 to 7.06 million worldwide. Unfortunately, the incidence of SCI is not registered in most countries (Cripps et al., 2011). In the United States, 10,000 to 12,000 new injuries occur every year (according to NIH, US department of Health and Human Services, 2012); in China, this number is much larger; over 60,000 new injuries are added each year (Qiu, 2009). It is also estimated that currently 12,000 Australians are living with spinal cord injuries, while 350-400 new cases are added each year (O'Connor, 2005.

The world report on disability (WHO, 2011) stated that the average lifetime cost is estimated to be $5 million for paraplegia and $9.5 million for quadriplegia per incidence. At the same time, in the USA, the average lifetime cost of patients with SCI is estimated to be around $9.7 million, and the annual medical cost ranges from $15,000 to $30,000 per year (French et al., 2007). In contrast, the total lifetime cost for SCI is very high in Australia compared to other countries; it’s estimated to be $2 billion (AUD) per year (O'Donnell et al., 2009, Collie et al., 2010).

According to statistics, among all spinal cord injuries, roughly half of the patients are paraplegics (Mirahmadi et al., 1982). It is also found that these patients prefer restoration of walking as one of the top priorities among all other complications such as pressure sores, inability of temperature and blood pressure regulation, and loss of bladder and bowel control (Anderson, 2004). Furthermore, sexual function is frequently impaired or lost with SCI (Benevento and Sipski, 2002). Hence, it is very important to find out the solution to “cure paralysis”.

Unfortunately, there is no complete cure for SCI at the moment (Thuret et al., 2006). However, physical rehabilitation following SCI aims to restore sensorimotor functions of these individuals so that they are able to become independent in their daily activities. There are two main strategies to accomplish this; one is functional recovery and the other comprises compensatory strategies. These strategies are used during an individual’s rehabilitation program. The recovery strategies are dependent on several factors including severity of the injury, level of the lesion, resource availability, level of family and community support, and clinical practice guidelines developed by physiotherapists and physicians. In cases of severe or complete paraplegia, daily activities like transferring body weight from one place to another (such as from bed to wheelchair or car) are typically accomplished using compensatory strategies, such as focusing on strengthening and utilizing unaffected arms and hands. Less severe or incomplete injuries offer a greater chance of recovery of functions, thereby warranting the use of functional recovery strategies (Harkema et al., 2012). In this chapter, we are going to discuss available therapies for the rehabilitation of paraplegic patients, and a new neuroprosthetic approach for restoring walking after complete SCI.