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).
|Advantages of Nerve Transfers
||Drawbacks of Nerve Transfers
- Less surgical dissection, recovery time and scarring (Brown 2012; Keith & Peljovich 2012).
- Only one surgical procedure to reconstruct finger flexion and extension (Revol et al., 2002; Brown 2012).
- Decreased dependence on care for ADL after surgery (Bertelli et al., 2011; Brown 2012; Hentz 2002).
- Less restrictive immobilization after surgery, with less pain and minimal loss of muscle function (Brown 2011; Brown 2012).
- Greater functional gains (Brown 2011; Brown 2012; Brown et al., 2012).
- Multiple functions may be activated by a single nerve (Brown 2011; Brown 2012; Midha 2004).
- When an improperly selected donor nerve with suboptimal function is transplanted it may significantly downgrade function (Senjaya & Midha 2013).
- The donating muscle may be entirely denervated and lose its function (Senjaya & Midha 2013).
- Central motor re-education is challenging, especially for nerve transfers from non-synergistic nerves (Senjaya & Midha 2013).
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.
Total Sample Size
|Fox et al., 2015b
Population: Mean Age: 28 yr; Gender: males=6, females=1; Level of Injury: C4=2, C5=2, C6=3; Severity of Injury: AIS A=4, AIS B=2, AIS C=1.
Intervention: Patients receiving nerve transfer surgery completed assessments and self-reports, and were prospectively followed-up over a minimum of 12 mo. Nerve tissue was also collected during surgery. Surgeries included Brachialis (BR) to the anterior interosseous nerve (AIN; n=7), BR to the flexor carpi radialis (FCR; n=5), BR to the flexor digitorum superficialis (FDS; n=3), supinator to extensor carpi ulnaris (ECU; n=1), supinator to posterior interosseous nerve (PIN; n=1), deltoid-to-triceps (n=1), and exploratory surgery (n=1). Assessments were conducted at baseline and at 2,4 and 12 wk post-surgery.
Outcome Measures: Medical Research Council elbow flexion grade (MRC), Histomorphometric analysis, Complications post-surgery, Functional gains reported by patients.
1. Histomorphometric analysis revealed excellent functioning of the transferred nerves.
2. One patient experienced a reduced fiber density, heterogeneity of fibers, and imperfect architecture of the nerve cell after histomorphometric analysis, however, this patient was found to have low motor neuron involvement at the time of surgery.
3. No patients experienced a decline in postoperative functioning compared to baseline functioning according to MRC scores.
4. One patient who underwent deltoid-to-triceps transfer experienced postoperative weakness of the deltoid (MRC grade 4) but eventually subsided and strength returned to baseline levels (MRC grade 5).
5. Functional gains as according to patient self-reports included an improvement in grasp strength (n=2), greater wrist stability (n=1), an improvement in pinch activity (n=1), and greater use of their hand for activities such as feeding and using a cell phone (n=1).
6. Two patients did not report any changes in functioning from pre-surgery to post-surgery.
7. Four patients experienced minor complications including paresthesia of the thumb (n=2), hypesthesia of the thumb (n=1), and a seroma which required drainage (n=1).
8. Two patients experienced major complications including urosepsis (n=1) and a urinary tract infection (n=1).
|Bertelli et al., 2017
Population: Mean age=28±15 yr; Gender: males=8, females=1; Time since injury: 7.6±4 mo; Level of injury: C5 – C7; Severity of injury: AISA A=9.
Intervention: Participants received nerve transfer surgery for restoration of finger flexion in 17 upper limbs of nine patients. In three upper limbs, the nerve to the brachialis was transferred to the anterior interosseous nerve (AIN). In five upper limbs, the nerve to the brachialis was transferred to median nerve motor fascicles innervating finger flexion muscles in the mid arm. In four upper limbs, the nerve to the brachioradialis was transferred to the AIN. In the remaining five upper limbs, the nerve to the extensor carpi radialis brevis (ECRB) was transferred to the AIN. Outcome measures were assessed at baseline and 16±6 mo.
Outcome Measures: Manual muscle test (range of finger flexion and strength).
1. A recovery of M3 or better in finger flexion strength was observed in 10 out of 17 surgically treated limbs.
2. Restoration of finger flexion was observed in four out of eight upper limbs in which the nerve to the brachialis was used; Range of motion was incomplete in all five of these limbs and strength was greater than M3 in all limbs.
3. Full finger flexion with M4 strength was observed in all five upper limbs, where the ECRB was transferred to the AIN.
|Bertelli et al., 2015
Population: Mean age: 26 yr; Gender: males=6, females=1; Level of injury: complete C-6=7; Mean ASIA motor score: 15.8±3.9; Mean time since injury: 7 yr.
Intervention: 27 recipient nerves. Elbow, thumb and finger extension reconstruction via nerve transfer was performed on patients with midcervical spinal cord injuries on average 7 mo post injury and outcomes were reported.
Outcome Measures: British Medical Research Council scale (BMRC).
1. At time of final postoperative assessment, elbow extension scored BMRC Grade M4 and under full voluntary control in 11 upper limbs (UL) and in 2 UL within same patient, elbow extension scored Grade M3.
2. A BMRC Grade M4 for full thumb extension with wrist in neutral was observed in 8 UL and 4 hands had thumb extension that scored M3.
3. Full metacarpal extension scoring M4 was demonstrated in 12 hands.
4. Finger extension scoring M3 with only partial range of motion at the metacarpal phalangeal joint was observed in the remaining 1 limb.
5. All patients improved at self-transferring and controlling their wheelchairs.
6. After surgery, all patients extended their thumb and fingers without restriction, no decreased function at donor sites and no patient lost abduction strength or shoulder range.
|Fox et al., 2018
Population: <1 yr post SCI: Mean age=36.1±16 yr; Gender: males=7, females=2; Time since injury: <1 yr; Level of injury: not reported; Severity of injury: not reported.
>1 yr post SCI: Mean age=38.8±17 yr; Gender: males=22, females=5; Time since injury: >1 yr; Level of injury: not reported; Severity of injury: not reported.
Intervention: No intervention. Medical records of patients were reviewed to develop a diagnostic algorithm, focusing on electro diagnostic studies (EDX), to determine eligibility for nerve transfer surgery based on time of injury.
Outcome Measures: EDX data.
|1. Although no statistics were reported, a substantial number of patients presenting years after SCI are candidates for nerve transfers based on EDX data.
|Simcock et al., 2017
Population: Age range=15 to 80 yr; Gender: males=50, females=3; Time since injury: <1 yr; Level of injury: C2 – C8; Severity of injury: AISA A=21, B=19, C=8, D=5.
Intervention: No intervention. Case note review of medical records from 2007 to 2012 to identify patients that may benefit from nerve transfer surgery. Outcome measures were assessed at six wk, 12 wk and one yr following injury.
Outcome Measures: Neurological assessment.
1. Nerve transfer within 3 to 12 mo of injury provides active hand opening for patients following cervical SCI.
2. Neurological assessment identifies patients who may benefit from nerve transfer surgery to improve hand opening.
|Fox et al., 2015c
Population: Mean Age: 32.9 yr; Gender: males=7, females=1.
Intervention: Data was collected on patients who had received nerve transfer surgery and had been followed-up over a period of 12 mo. 20 surgeries were performed which included Brachialis (BR) to the anterior interosseous nerve (AIN; n=7), BR to the flexor carpi radialis (FCR; n=3), deltoid-to-triceps (n=3, 15%), BR to the AIN/flexor digitorum superficialis (FDS; n=1), BR to the FDS/FCR (n=1), BR to the AIN/FCR (n=1, BR to extensor carpi radialis (n=1), supinator to extensor carpi ulnaris (n=1), supinator to posterior interosseous nerve (n=1), and exploratory surgery (n=1). Assessments were conducted every 3 mos until 12 mos post-surgery.
Outcome Measures: Functional gain self-reports by patients, Medical Research Council elbow flexion grade (MRC), Complications post-surgery.
|1. Functional gains were reported from 6mos onwards according to patient self-reports which included increased grasp strength (n=2), an increased use of their hand for feeding (n=2), an increase in wrist stability (n=1), and improvement in pinch activities (n=1).
2. Three patients reported no changes or improvements since surgery.
3. All patients achieved grades of 1-3 on the MRC indicating a trace of contraction, active movement with gravity eliminated, and active movement against gravity respectively.
4. Complications post-surgery included paresthesias of the thumb (n=3), urinary tract infection with sepsis (n=1), and seroma (n=1).
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.