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Introduction

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Raineteau and Schwab (2001) define spinal cord injury (SCI) as a lesion within the spinal cord that results in the disruption of nerve fibre bundles that convey ascending sensory and descending motor information.

The level at which the injury or lesion occurs and the completeness of the lesion (incomplete or complete) dictate the level of independence of the affected individual (Ditunno 1999). If a SCI occurs above or within the cervical levels (C1 – C8), upper and lower extremity motor and/or sensory function is affected (Witiw and Fehlings 2015). In contrast, if a SCI occurs between T1 – L5, upper extremity function is preserved, while lower extremity motor/sensory function is impaired (Witiw and Fehlings 2015). It is estimated that cervical SCI accounts for approximately 50% of all people living with SCI (Steeves et al., 2007).

Level of function/independence is also influenced by completeness of the lesion. In complete spinal cord injuries, no neural transmission occurs below the point of injury, resulting in a complete loss of function below the point of injury (Courtine & Sofroniew 2019). In contrast, some neural transmission can still pass through the spinal cord in incomplete lesions. (Courtine & Sofroniew 2019).

The World Health Organization estimates that between 250 000 and 500 000 people experience a SCI each year (WHO, 2013). Due to advances in surgical procedures, supportive measures and rehabilitation protocols, functional outcomes have improved and the rate of morbidity has decreased (Ahuja et al., 2017). However, many functional deficits remain and individuals experience permanent disabilities (Anderson, 2004; Courtine et al., 2019). The loss of upper extremity function, especially the use of the hands, is one of the most significant and devastating losses an individual can experience. The use of the upper extremities is critical in completing basic activities of daily living (ADL) such as self-feeding, dressing, bathing, and toileting. Mobility also require significant upper extremity function, such as transfers from surface to surface, transitional movements such as rolling, bridging and sit to lie, crutch walking and wheeled mobility (Snoek et al. 2004).

Hanson and Franklin (1976) compared sexual function to three other impairments in patients with SCI; approximately 76% of the subjects gave the highest priority to upper extremity function. Snoek et al. (2004) surveyed the needs of patients with SCI and found a high impact and high priority for improvement in hand function in those with tetraplegia comparable to that for bladder and bowel dysfunction. A study by Anderson (2004) found similar results in which 48.7% of persons with tetraplegia (and 3.3% of persons with paraplegia) reported that regaining arm and hand function would most improve their quality of life. These findings did not differ by gender or number of years post SCI which suggests that recovering even partial arm and hand function may have a significant impact on the independence of many spinal cord individuals (Anderson et al., 2004).

To lessen the impact of negative functional outcomes in motor recovery, functional independence, social integration and quality of life in individuals with SCI, clinical practice guidelines were developed by the Paralyzed Veterans Association (Consortium for Spinal Cord Medicine 2005). These guidelines outline the expected skills/outcomes that should be achieved at each significant level of injury and help guide physicians in the management of primary and secondary complications (Consortium for Spinal Cord Medicine 2005). Secondary complications from SCI present ongoing challenges for upper extremity function and include pain, spasticity, contractures and upper limb musculoskeletal injuries (Sipski & Richards 2006).

The initial care, management, rehabilitation, and prevention of injuries in the upper limb of those with tetraplegia is of great importance in maximizing and maintaining independence. However, management of the tetraplegic upper limb tends to be eclectic, involving functional strength training (repetition-heavy movements of ADL), orthoses and upper extremity surgery. Typically, treatment of upper extremity loss of function follows a stepwise approach, with conservative treatment methods applied first, followed by functional electrical stimulation and surgical interventions (Bryden et al., 2005). In addition, treatment of the upper limb is often divided into three phases: acute, subacute and reconstruction (Murphy and Chuinard 1998). The aims of the first two phases are to prevent complications, achieve optimal functioning within the limits of the neurological deficit and to create optimal conditions for the reconstructive phase (Bedbrook 1981; Curtin 1994; Harvey 1996; Keith & Lacey 1991). In the latter phase, various surgical options and FES help to improve positioning and stabilization of the arm as well as key and palmar grasp function (Johnstone et al., 1988; Peckham et al., 2001; Snoek et al., 2000; Triolo et al., 1996; Waters et al., 1996). The overall goal of reconstructive surgeries (e.g. muscle/tendon transpositions of the intact arm or hand muscles) is to substitute for lost motor function (van Tuijl et al., 2002). According to Moberg (1975), over 60% of individuals with tetraplegia could benefit from reconstructive surgery (improve overall functioning and independence) (Snoek et al., 2004) and as such, surgical reconstruction is often advocated. However, suitable candidates often do not accept the treatment that is offered. Curtin et al. (2005) reported that fewer than 10% of persons with tetraplegia undergo surgical reconstruction.

Despite publication of clinical practice guidelines (Consortium for Spinal Cord Medicine 2005; Consotrtium for Spinal Cord Medicine, 1999), there is little consensus regarding the management of the tetraplegic upper limb. However, this may be due to variations in muscle function after SCI (Thomas et al., 2014). Understanding the diversity of SCI is important in ensuring that therapy is tailored to each individual and that feedback is elicited from patient’s regarding their perceptions of the usefulness of specific interventions (Thomas et al., 2014). Hummel et al. (2005), Snoek et al. (2005) and the Consortium for Spinal Cord Medicine (2005) provide excellent recommendations as a starting point for the management of the tetraplegic upper limb.

Rehabilitation and management of an individual with SCI requires an interdisciplinary team approach during the acute phase of rehabilitation. The level and classification of the injury is determined, and the goals of maintaining range of motion (ROM), improving strength, managing tone, spasticity, and the prevention of secondary complications to achieve the person’s maximum functional ability for independent transfers, ADL and mobility are developed (Drolet et al., 1999; Haisma et al., 2006; Sipski & Richards 2006). Clinicians must be knowledgeable about the change in physical capacity based on level of injury as a prerequisite to developing optimal rehabilitation programs and for setting realistic individual rehabilitation goals.

The main focus of SCI rehabilitation is to train individuals on how to use their remaining sensorimotor systems to compensate for functional loss (van Tuijl et al., 2002). Rehabilitation strategies that utilize this method often demonstrate significant improvements in function after incomplete and complete SCI (Beekhuizen 2005; Bradbury et al., 2002; Buchuli & Schwab 2005; Curt et al., 2008; Kirshblum et al., 2004; Marino et al., 1999; Waters et al., 1994). Functional improvements are thought to arise from new motor control strategies that the central nervous system (CNS) uses to govern various movements. In able bodied individuals, motor control strategies are determined by the CNS, which activates predefined combinations of muscles (muscle synergies) to perform a task, rather than explicitly controlling individual muscles (Zariffa et al., 2012a). This body of research could have important implications in nerurorehabilitation, whereby retraining of muscle synergies through task performance may train the CNS to activate new motor control strategies. This process of “retraining” is known as adaptive plasticity (Frullo et al., 2017). The literature reporting on the presence of muscle synergies that involve a motor control paradigm is being actively investigated (Bizzi et al., 2008; Cheung et al., 2005; d’Avella et al., 2003; Overduin et al., 2008). This information may be useful in guiding the rehabilitation process after cervical SCI and ensuring that the exercises performed for the hand and upper limb are effective for restoring functional ability (Backus 2010).