Recently, nerve transfers have evolved as an alternative surgical approach to tendon transfers, to improve the functional ability of the hand and upper limb post SCI (Keith & Peljovich 2012). The advantages and potential drawbacks of utilizing nerve transfers over tendon transfers are listed in Table 24. A nerve transfer utilizes a proximal foreign nerve as a donor to re-innervate and repair distal denervated targets (Addas & Midha 2009; Brown et al., 2012; Midha 2004). The function of the transferred donor nerve is sacrificed to revive function in the recipient nerve and muscles, which are considered functionally more critical than the donor nerve (Senjaya & Midha 2013). Traditionally, nerve transfers were performed for brachial plexus injuries. However, more recently the transfer of the brachialis to the anterior interosseous nerve has been applied for SCI (Hawasli et al., 2015).
Prior to considering surgery, a detailed and careful assessment must be completed. Coulet et al. (2002) recommend assessing the extent of lower motor neuron (LMN) injury and muscle functionality. Lower motor neurons should be assessed to determine the extent of SCI via evaluation of tone, trophic status, deep tendon reflex, joint ROM, deformities, and electrodiagnostic studies. Following assessment of LMNs and muscle function, priority of functional restoration must be determined. Kozin (2002) recommended restoring elbow extension function first, followed by pinch and lastly grasp/release to restore hand function.
For nerve transfers around the level of the SCI (lesional level myotomes), surgery should be performed after a re-innervation window of at least six months, to ensure spontaneous recovery is achieved (Bertelli et al. 2011). However, re-innervation of muscle innervated by an infralesional segment is not time-dependent and can be performed years after injury (Bertelli et al., 2011).
Lastly, in order for a nerve transfer to be successful, a set of fundamental principles should be met (Senjaya & Midha, 2013; Midha et al., 2004):
- The recipient nerve should be repaired as close as possible to the target muscle to
ensure: the shortest amount of time for re-innervation, minimize distal denervation and
motor end plate changes.
- The donor nerve should be from a muscle with expendable function or redundant
- The nerve repair should be performed directly without intervening grafts.
- Donor muscle with pure motor fibers should be used to maximize the muscle fiber reinnervation.
- The donor nerve should have a large number of motor axons and be a reasonable size
match to the recipient nerve.
- The donor nerve should have a synergistic function to the muscle reconstructed to
facilitate motor re-education.
- Clinicians should be mindful that motor re-education improves functional recovery post
Upon review of the existing literature, six studies investigating the use of nerve transfer for restoration of upper extremity function in tetraplegic patients were identified. The methodological details and results of these studies are presented in Table 25.
Restoration of upper extremity function in individuals with SCI is essential to complete many activities of daily living including the ability to perform pressure relief maneuvers, push a manual wheelchair, reach for items and objects above shoulder height, and to complete functional transfers. Nerve transfer surgery has emerged as a promising technique for restoration of upper extremity function after SCI, which has many advantages over traditional tendon transfers.
To date, a small number of studies have been published that focus on nerve transfer surgery. Despite this, nerve transfer appears to be a relatively safe and effective surgical alternative to tendon transfer. Fox and colleagues (2015b) found that the risk of postoperative decline is low, and the majority of patients report improvements in upper extremity function across a variety of different nerve transfer procedures. Additionally, one study found that regardless of timing (<1 or >1 yr post-injury), nerve transfer surgery is effective in restoring hand function (Simcock et al., 2017; Fox et al., 2018). Most importantly, all studies that investigated functionality and grasp strength reported beneficial outcomes in the majority of patients; however, not all patients have successful surgical outcomes. In this sense, candidates for nerve transfer surgery should be carefully selected. Regardless, the ability of nerve transfers to restore upper extremity function in the majority of SCI patients is quite promising and has the potential to impact patient quality of life, as well as independence. Future research should focus on determining the optimal timing for surgery and outcome after a combination of treatments (e.g. tendon and nerve transfer).
There is level 2 evidence (from one cohort study: Fox et al. 2015b) that the risk of negative outcomes for nerve transfer surgery, such as postoperative decline compared to baseline, are low.
There is level 4 evidence (from one pre-post and one post-test study: Bertelli et al. 2017; Bertelli et al. 2015) that nerve transfer surgery can increase motor hand function without compromising donor site function in patients with SCI.
There is level 4 evidence (from one case series: Fox et al. 2018) that patients presenting years after SCI are eligible candidates for nerve transfer surgery.
There is level 4 evidence (from two case series: Simcock et al. 2017; Fox et al. 2015a) that nerve transfer surgery can increase functionality and grasp strength in some patients, however not all patients have successful surgical outcomes.