By Kal Kaur
Table of content
Mechanisms of SCI
Secondary injury to SCI
Prevalence of spinal cord injuries
The main principle for introducing automated critical care technology for patients with spinal cord injury (SCI) is to give back to these sufferers an element of independence and a sense of normality. Patients with spinal cord injuries as a result of neurological disease or a physical trauma are faced with a never-ending battle to maintain physical communication with the outside world. Spinal cord injuries can result in complete paralysis of the lower limbs depending on exactly where along the spinal cord the injury has occurred (See figure 1).
In more extreme cases, spinal cord injuries can be completely debilitating and result in conditions, such as ‘Locked-in syndrome’ where the patient is conscious and aware of their surroundings, but has complete loss of function in the majority of voluntary muscles that control the body apart from eye movement. For sufferers of SCI, having to deal with the reality of loss of control over the function of their body is emotionally a long-term battle, which has become a motivation for scientists to research on how to evolve current-day rehabilitation methods that restores minimal functional ability for SCI patients’ into robot-aided communication with the use of sensors that could potentially help the sufferer perform more than just limited tasks.
Figure 1. Basic mechanisms of SCI. This video animation clearly demonstrates the etiology of an SCI and highlights the secondary damage.
Mechanisms of SCI
- An SCI will typically involve a large force, laceration (e.g., impact from a missile, varying degrees of sharp bone fragment dislocation, or severe distraction of the spinal cord), or a certain level of compression to the spinal cord. Such physical trauma can, at the site of injury, fracture the bone, spinal cord disc. If the trauma is destructive enough it will damage the ligamentous tissue that holds the blood vessels, axons, the oligodendriocytes (cells that support the axon), and neighbouring neurons.
Secondary injury to SCI
- Physical damage to the spinal cord sets off a series of physiological abnormalities whereby the blood vessels that support the ligamentous tissue stop working, which disrupts blood circulation to the spinal cord tissue and deprives the tissue of oxygen (i.e., hypoxia), causing axonal and neuronal cell death.
- Demyelination and neuronal cell death result in the release of glutamate, which over-excites surrounding neurons, forcing these neurons to generate a dangerous influx of calcium, thus exacerbating cell death of surrounding healthy neuronal tissue. This signalling process is fundamental to understand when building a neural interface system – a concept discussed later in this article – that can work in conjunction with automated technology that links the gap between command from the brain and effect from the robot.
Prevalence of spinal cord injuries
Based on a report by the National Spinal Cord Injury Statistical Center, Birmingham, Alabama, observing the incidents of SCI since 1900’s, there are upon estimation 40 cases per 1 million population in the United States of America (USA). On average, 12,000 new cases of SCI are reported each year. The prevalence of SCI in USA among sufferers still alive in 2010 ranged from 232,000 to 316,000 cases, which again demonstrates the need to direct research that can move standard care for SCI to the potential of automated and sensor driven technology to benefit the lives of so many SCI sufferers.
A ground-breaking case study was recently published by Brown University, reporting on a patient “S3” who is a sufferer of tetraplegia (a condition where the SCI results in total paralysis of limbs and the torso). After 15 years of suffering from this condition, this patient was able to use a robotic arm controlled by thought, connected via a neural interface system (NIS) to aid her in serving herself a drink for the first time since injury. The BrainGait NIS was used in this research along with the DEKA robotic arm.
The BrainGait NIS is a novel piece of research technology that is based on the concept that a sensor is placed in the area of the brain that is responsible for controlling movement can sense, transmit, and process the electrical activity of individual neurons. The sensor is made of a silicon array that occupies approximately 100 electrodes, a device that is then implanted into the motor cortex area of the brain that controls movement of the limbs. The neural activity is detected by the sensor implanted in the motor cortex which transmits this signal to an operator that works in conjunction with a software system to transform the brain signal into a command for the external device (i.e., a robotic limb) (figure 2).
Figure 2. A demonstration of the BrainGate NIS developed by Cyberkinetics Inc.
A trial by J.D. Simeral, et al (2011) measured neural cursor control and found that across a five-day testing period, neuronal spiking signals were measured from 41 out of 96 electrodes and then decoded to aid cursor point-and-click function, which demonstrates the validity of using a NIS in patients with no limb control.
The BainGate system is still being used in research with the aim that at some point in the near future, this interface system will be more flexible in being able to control thought. BrainGate also aims to complement the neural interface implant with an effective prosthetic limb that can be manipulated by the controller to allow for ease of use. Therefore, compared to normal rehabilitation programs that are used (for example, physiotherapy to encourage muscle strengthening and wheelchair mobility, which can be a long-term struggle for the sufferer), using the NIS with a controlled prosthetic limb, allows the sufferer to independently regain control of actions without any struggle.
Thought-controlled robotics is a fresh step in the right direction for its application as critical care systems. Though BrainGate currently may be the most advanced technology for turning thought into action using a sensor and a robotic arm, there are robotic devices currently on the market that aid in the rehabilitation of SCI sufferers. For example, Ekso Bionics design and manufacture wearable robots for people suffering from lower-limb paralysis. In 2010, Ekso Bionics, introduced the eLEGS – a bionic exoskeleton that allows and supports wheelchair users to stand up and to assist them in walking again. The eLEGS is an intelligent device powered by a battery and with motor and sensor stimuli, in combination with balance and positioning of the body, the user can start to walk and re-establish a gait pattern (figure 3).
Figure 3. A demonstration of how patients are using the eLEGS device.
Like the eLEGS, there are few other working examples of battery-assisted wearable exoskeletons, but such technology is not yet widely distributed among sufferers. A similar concept to the eLEGS bionic robot named the ReWalk has been introduced by Argo Medical Technologies Ltd and is commercially available. The ReWalk is an alternative mobility solution for sufferers of an SCI whom have been confined to a wheelchair. This product allows the sufferer to stand up, establish a gait pattern, and ascend and descend stairs. The product is a wearable brace support that can control and move the joints using actuation motors and integrates this with sensors that receive a command. The command from the sensor is then interpreted by a computer system with control and safety algorithms, with all components functioning by the application of a rechargeable battery. figure 4 is a demonstration of how a wheelchair bound suffer of SCI can use the ReWalk device to regain independence and walk.
Figure 4. ReWalk - wearable bionic robot for SCI sufferers to help them walk once again.
The development in the application of robotics as an alternative to standard physiotherapeutic methods of rehabilitation for SCI sufferers is still a battle, and research into this field still needs to address the limitations to the use of robotic prosthesis and NIS. Wearable robots fall at a limitation when considering stroke patients whom have poor joint stability making it difficult for them to control and position the exoskeleton device. For SCI sufferers using an exoskeleton device, there may be incomplete unloading of the lower limb when the patient is trying to establish a regular gait pattern. There is also the issue of how much a standard exoskeleton wearable robot will weigh, whether this is manageable by the patient, and how this may affect the motion or strength of the physical limbs.
When considering more advanced and intricate technology, such as the NIS for the rehabilitation of SCI sufferers, there are many challenges that lie ahead. For example, research needs to focus on ways of measuring long-term stability of the sensor used in the NIS technique as this will assess the quality of this method. Furthermore, electrode arrays that are used to record action potentials during neural activity need to be tested for their use over extended periods of time to help develop a sensor that can achieve long-term viability . Use of an implantable sensor in the brain also raises concerns about infection at the site of the implant. It is also important to remember that complicated electronic devices can generate a large amount of heat and so there is a need to weigh this risk with the length of time this device will be used to aid with mapping a signalling process . For SCI sufferers, the ease and time of use for NIS technology will be fundamental to helping achieve normality in daily life, but to also help enhance the efficacy in therapy that can be offered by clinicians.
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