**2.3 WISCI II**

The Walking Index for Spinal Cord Injury II is a reliable and trustworthy tool to measure walking improvement in SCI patients [13]. It comprises 21 levels that evaluate gait, considering the use of walking aids. It goes from 0 (the patient is not able to walk) to 20 (the patient walks at least 10 m without crutches or assistance) [14].

#### **2.4 SF-36**

The Short-Form Health Survey questionnaire is a nonspecific generic test broadly used to evaluate the quality of life, considering both positive and negative subjects, in patients with chronic conditions and mobility diseases [15]. It is easy to answer and takes approximately 5 to 10 min.

The test comprises 36 items, divided into 8 subscales that evaluate the following areas: physical function (10 items), role limitations due to physical issues (4 items), pain (2 items), general health appreciation (5 items), vitality (4 items), social function (2 items), role limitations due to emotional issues (3 items), mental health (5 items), and an additional item that compares actual health with previous year perception of health [16]. Many studies have found with this instrument that SCI has a negative influence on the quality of life of patients [17].

#### **3. Rehabilitation strategies**

SCI is a neurological condition that demands a long rehabilitation period, coordinated by a multidisciplinary team because of the damage that it entails. To avoid complications as much as possible, to improve function, and to achieve the most independence, numerous rehabilitation strategies have been shown in many studies to have an impact in patient recovery; some of them are the following: strength, range of movement and stretching exercises, functional electrical stimulation (FES), epidural electrical stimulation (EES) of the spinal cord, occupational therapy, dry needling, and exoskeleton.

#### **3.1 Range of movement, strength, and stretching exercises**

Range of movement refers to the normal movement of a joint; hence range of movement exercises are those that promote joint mobility and flexibility.

#### *Paraplegia*

Studies have observed that these exercises improve function for daily life activities [18], prevent contractures, protect tenodesis effect [19], strengthen paralyzed muscles, promote nerve and cerebral remodeling, and improve spinal microenvironment and functional prognosis [20]. For protection of the joint structure and preservation of muscle tone, sandbags, pillows, or orthotics are usually used. Exercise is important for strengthening the muscles of the upper limbs, emphasizing on rotation of the shoulders for the use of crutches or wheelchair. These exercises will help in the mobilization and independence in daily life activities. In patients with incomplete SCI, walking potential is high, so sitting, parallel bars, and balance exercises should be done [19].

#### **3.2 Functional electrical stimulation**

Functional electrical stimulation is a technique that artificially activates sensorymotor systems through electrical current pulses, producing action potentials in afferent and efferent neural pathways to stimulate muscles and generate movement [21]. This procedure is added to other therapies to increase mobility, sensory feedback, and muscle activity to decrease atrophy. It also provides cardiorespiratory fitness; improves posture and trunk stability [22]; prevents contractures, pressure ulcers, and orthostatic hypotension [23]; promotes nerve restoration; and prevents peripheral nerve deterioration [24].

Functional electrical stimulation is a technique that artificially activates sensorymotor systems through electrical current pulses, producing action potentials in afferent and efferent neural pathways to stimulate muscles and generate movement [21]. The main elements of a FES system are the battery, an electronic stimulator, control unit, wiring, and electrodes. The controller can work through a switch, joystick, or voice. There are different types of electrodes, superficial, intramuscular percutaneous, implantable, and epimysial; however the commercially available are the superficial ones, which should be placed over the skin above the nerves to be stimulated; the rest of the electrodes are for research purpose only. The electrodes must be of low-impedance, flexible, and easy to don and doff [22]. The electrical parameters of these systems are waveforms, amplitude, pulse width, reciprocity, ramp, and duration; all of these are combined to generate an electrical current and must be adjusted to achieve the desired response [22, 23].

It is important to evaluate the patient to determine if he or she is a candidate for this therapy. Some exclusion criteria for FES are the following: if the patient has an electrical implantable device, history of cancer, osteomyelitis, epilepsy, and thrombosis [23].

FES systems can be applied to different sites. In patients with cervical SCI, hand function recovery is the main priority, so there are FES systems developed for the upper limb that work through neuroprosthetics with a stimulator for forearm and hand muscles; patients with injuries at C5-C6 level can benefit with this therapy. The only commercially available systems for the upper limb are NESSH200 and Compex. NESSH200 consists of an adjustable wrist prosthetic with five electrodes for finger flexors and extensors, allowing handgrip [24, 25]. There are FES systems for lower limbs that allow sitting and mobility. The best candidates for this therapy are patients with injuries at T4-T12 level, which have more impact in patients with incomplete injuries. The FES neuroprosthetics for the lower limbs stimulate the knees and hips [24]. A commercially available FES system in the USA is the Parastep, which works through 4–6 channels to stimulate the quadriceps and gluteal muscles. Battery is placed on the waist and controls are over a walker [25]. FES cycling systems are also commercially available; one of them is developed by Restorative Therapies, Inc. [24] and the other one, ERGYS, developed by

Therapeutic Technologies, Inc. which has six electrodes to stimulate the quadriceps, hamstrings, and gluteal muscles [22].

This procedure is added to other therapies to increase mobility, sensory feedback, and muscle activity to decrease atrophy. It also provides cardiorespiratory fitness; improves posture and trunk stability [26]; prevents contractures, pressure ulcers, and orthostatic hypotension [27]; promotes nerve restoration; and prevents peripheral nerve deterioration [28].

### **3.3 Epidural electrical stimulation of the spinal cord**

This strategy requires a device to be implanted through a laminectomy over the dura mater of the spinal cord [25]. The device delivers a rhythmical afferent electrical current to posterior nerve roots to activate central circuits that regulate movement, pain, and the cardiorespiratory system [22].

It is believed that EES activates two pathways: The first one stimulates afferent dorsal pathways that synapse with motor neurons; the second pathway directly stimulates motor neurons through stimulation of efferent motor nerves [26].

Studies in SCI patients have shown that this strategy decreases fatigue [25], improves cardiovascular and respiratory fitness, increases lean body mass, and improves bladder voiding [26]. The main disadvantage of EES is that it requires surgery for device insertion, which implicates the risk of infection, hematoma, or injury because of the device [25].

This experimental strategy requires a device to be implanted through a laminectomy over the dura mater of the spinal cord [29]. The device delivers a rhythmical afferent electrical current to posterior nerve roots to activate central circuits that regulate movement, pain, and the cardiorespiratory system [26].

It is believed that EES activates two pathways: The first one stimulates afferent dorsal pathways that synapse with motor neurons; the second pathway directly stimulates motor neurons through stimulation of efferent motor nerves [30].

Studies in SCI patients have shown that this strategy decreases fatigue [29], improves cardiovascular and respiratory fitness, increases lean body mass, and improves bladder voiding [30]. The main disadvantages of EES are that it requires surgery for device insertion, which implicates the risk of infection, hematoma, or injury because of the device [29], it is expensive, and it does not yet establish a standard number of sessions and parameter configurations since multiple studies have shown that outcomes vary in each patient due to SCI heterogeneity [30].

It is worth mentioning that this technique is used merely for research purpose only and it is not approved by health authorities. The evidence that exists to date is not enough to justify its use, since it has been studied only in specific small cohorts of patients or single patients with SCI and there are no clinical trials with this method [29, 30].

### **3.4 Transcutaneous electrical nerve stimulation (TENS)**

TENS is a high- and low-frequency electrical current therapy. It is used for pain management, but many other benefits have been observed, such as balance and proprioception improvement and spasticity decrease [31]. To date, its mechanism of action is unknown; however, different theories assume it works by modulating inhibitory spinal circuits, by activating afferent neurons, or by inducing central nervous system plasticity [32]. When applying it, it is necessary to consider electrode positioning, frequency, and pulse intensity; though, there is not a consensus on how long sessions should last and how much frequency has to be applied. The main advantages of this therapy are that it is low cost, it is easy to

apply since the patient can do it by himself/herself, and there are no side effects reported yet [31, 33].
