A neurophysiological approach to nerve transfer to restore upper limb function in cervical spinal cord injury

Characterization of Spinal Cord Injury Patients for Arm Functional Restoration through Nerve Transfer

INTRODUCTION

Traumatic spinal cord injuries (tSCI) are common, often leaving patients irreparably debilitated. Therefore, novel strategies such as nerve transfers (NT) are needed for mitigating secondary SCI damage and improving function. Although different tSCI NT options exist, little is known about the epidemiological and injury-related aspects of this patient population. Here, we report such characteristics to better identify and understand the number and types of tSCI individuals who may benefit from NTs.

MATERIALS AND METHODS

Two peripheral nerve experts independently evaluated all adult tSCI individuals < 80 years old admitted with cervical tSCI (C1-T1) between 2005 and 2019 with documented tSCI severity using the ASIA Impairment Scale for suitability for NT (nerve donor with MRC strength ≥ 4/5 and recipient ≤ 2/5). Demographic, traumatic injury, and neurological injury variables were collected and analyzed.

RESULTS

A total of 709 tSCI individuals were identified with 224 (32%) who met the selection criteria for participation based on their tSCI level (C1-T1). Of these, 108 (15% of all tSCIs and 48% of all cervical tSCIs) were deemed to be appropriate NT candidates. Due to recovery, 6 NT candidates initially deem appropriate no longer qualified by their last follow-up. Conversely, 19 individuals not initially considered appropriate then become eligible by their last follow-up.

CONCLUSION

We found that a large proportion of individuals with cervical tSCI could potentially benefit from NTs. To our knowledge, this is the first study to detail the number of tSCI individuals that may qualify for NT from a large prospective database.

Nerve Transfer After Cervical Spinal Cord Injury: Who Has a "Time Sensitive" Injury Based on Electrodiagnostic Findings?

OBJECTIVE

To use the ulnar compound muscle action potential (CMAP) to abductor digiti minimi (ADM) to identify the proportion of individuals with cervical spinal cord injury (SCI) who have lower motor neuron (LMN) abnormalities involving the C8-T1 spinal nerve roots, within 3-6 months, and thus may influence the response to nerve transfer surgery.

DESIGN

Retrospective analysis of prospectively collected data. Data were analyzed from European Multicenter Study About SCI database.

SETTING

Multi-center, academic hospitals.

PARTICIPANTS

We included 79 subjects (age=41.4±17.7, range:16-75; 59 men; N=79), who were classified as cervical level injuries 2 weeks after injury and who had manual muscle strength examinations that would warrant consideration for nerve transfer (C5≥4, C8<3).

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

The ulnar nerve CMAP amplitude to ADM was used as a proxy measure for C8-T1 spinal segment health. CMAP amplitude was stratified into very abnormal (<1.0 mV), sub-normal (1.0-5.9 mV), and normal (>6.0 mV). Analysis took place at 3 (n=148 limbs) and 6 months (n=145 limbs).

RESULTS

At 3- and 6-month post-injury, 33.1% and 28.3% of limbs had very abnormal CMAP amplitudes, respectively, while in 54.1% and 51.7%, CMAPs were sub-normal. Median change in amplitude from 3 to 6 months was 0.0 mV for very abnormal and 1.0 mV for subnormal groups. A 3-month ulnar CMAP <1 mV had a positive predictive value of 0.73 (95% CI 0.69-0.76) and 0.78 (95% CI 0.75-0.80) for C8 and T1 muscle strength of 0 vs 1 or 2.

CONCLUSION

A high proportion of individuals have ulnar CMAPs below the lower limit of normal 3- and 6-month post cervical SCI and may also have intercurrent LMN injury. Failure to identify individuals with LMN denervation could result in a lost opportunity to improve hand function through timely nerve transfer surgeries.

Axillary to Radial Nerve Transfer for Recovery of Elbow Extension After Spinal Cord Injury

BACKGROUND AND OBJECTIVES

Cervical spinal cord injuries (SCI) result in severe loss of function and independence. Nerve transfers have become a powerful method for restoring upper extremity function, the most critical missing function desired by this patient population. Recovery of active elbow extension allows for expansion of one's workspace to reach for objects and stabilizes control at the elbow joint. Without triceps function, a patient with a cervical SCI is rendered entirely helpless when in the supine position. Our objective was to provide a concise description of the transfer of branches of the axillary nerve (AN) to the long head of the triceps branch of the radial nerve (RN) for restoration of elbow extension after cervical SCI.

METHODS

An anterior, axillary approach is used for the transfer of the nerve branches of the AN (which may include branches to the teres minor, posterior deltoid, or even middle deltoid) to the long head of the triceps branch of the RN. Preoperative assessment and intraoperative stimulation are demonstrated to direct optimal selection of axillary branch donors.

RESULTS

The axillary approach provides full access to all branches of the AN in optimal proximity to triceps branches of the RN and allows for tension-free coaptation to achieve successful recovery of elbow extension. Final outcomes may not be achieved for 18 months. Of our last 20 patients with greater than 12-month follow-up, 13 have achieved antigravity strength in elbow extension, 4 are demonstrating ongoing progression, and 3 are definitive failures by 18 months.

CONCLUSION

The axillary to RN transfer is an important intervention for recovery of elbow extension after cervical SCI, which significantly improves quality of life in this patient population. Further large population outcomes studies are necessary to further establish efficacy and increase awareness of these procedures.

Predicting strength outcomes for upper limb nerve transfer surgery in tetraplegia

We report a retrospective study of 112 nerve transfers in 39 participants to investigate predictors of strength outcomes after nerve transfer surgery for upper limb reanimation in tetraplegia. We measured clinical and pre- and intraoperative neurophysiological assessment variables and compared them with strength outcomes 2 years after nerve transfer surgery. We found statistically significant improvement in Medical Research Council strength grades after nerve transfer surgery with lower cervical spine injuries (between one and two grades), lower donor nerve stimulation thresholds (half of a grade), greater motor evoked potential activity in recipient nerves (half of a grade) and greater muscle responses to intraoperative stimulation of donor (half of a grade) and recipient nerves (half of a grade).Level of evidence: III.

Clinical electrodiagnostic evaluation for nerve transfer surgery in spinal cord injury: a new indication and clinical pearls

In this review, we highlight the important role of the clinical electrodiagnostic (EDX) evaluation after cervical spinal cord injury (SCI). Our discussion focuses on the need for timely, frequent, and accurate EDX evaluations in the context of nerve transfer surgery to restore critical upper limb functions, including elbow extension, hand opening, and hand closing. The EDX evaluation is crucial to define the extent of lower motor neuron lesions and determine candidacy for surgery. We also discuss the important role of the postoperative EDX evaluation in determining prognosis and supporting rehabilitation. We propose a practical framework for EDX evaluation in this clinical setting.

Pre-operative electrodiagnostic planning for upper limb peripheral nerve transfers in cervical spinal cord injury: A Narrative Review

Peripheral nerve transfer (PNT) to improve upper limb function following cervical spinal cord injury (SCI) involves the transfer of supralesional donor nerves under voluntary control to intralesional or sublesional lower motor neurons not under voluntary control. Appropriate selection of donor and recipient nerves and surgical timing impact functional outcomes. While the gold standard of nerve selection is intra-operative nerve stimulation, preoperative electrodiagnostic (EDX) evaluation may help guide surgical planning. Currently there is no standardized preoperative EDX protocol. This study reviews the EDX workup preceding peripheral nerve transfer surgery in cervical SCI, and proposes an informed EDX protocol to assist with surgical planning. The PICO (Population, Intervention, Comparison, Outcome) framework was used to formulate relevant MeSH terms and identify published cases of PNT in cervical SCI in Medline, Embase, CINAHL, and Emcare databases in the last 10 years. The electrodiagnostic techniques evaluating putative donor nerves, recipient nerve branches, time-sensitivity of nerve transfer and other electrophysiological parameters were summarized to guide creation of a preoperative EDX protocol. Needle electromyography (EMG) was the most commonly used EDX technique to identify healthy donor nerves. Although needle EMG has also been used on recipient nerves, compound muscle action potential (CMAP) amplitudes may provide a more accurate determination of recipient nerve health and time-sensitivity for nerve transfer. While there has been progress in pre-surgical EDX evaluation, EMG and NCS approaches are quite variable, and each has limitations in their utility for pre-operative planning. There is need for standardization in the EDX evaluation preceding peripheral nerve transfer surgery to assist with donor and recipient nerve selection, surgical timing and to optimize outcomes. Based on results of this review, herein we propose the PreSCIse (PRotocol for Electrodiagnosis in SCI Surgery of the upper Extremity) pre-operative EDX panel to achieve said goals through an interdisciplinary and patient-centered approach. This article is protected by copyright. All rights reserved.

Surface EMG in Subacute and Chronic Care after Traumatic Spinal Cord Injuries

Background: Traumatic spinal cord injury (SCI) is a devastating condition commonly originating from motor vehicle accidents or falls. Trauma care after SCI is challenging; after decompression surgery and spine stabilization, the first step is to assess the location and severity of the traumatic lesion. For this, clinical outcome measures are used to quantify the residual sensation and volitional control of muscles below the level of injury. These clinical assessments are important for decision-making, including the prediction of the recovery potential of individuals after the SCI. In clinical care, this quantification is usually performed using sensation and motor scores, a semi-quantitative measurement, alongside the binary classification of the sacral sparing (yes/no). Objective: In this perspective article, I review the use of surface EMG (sEMG) as a quantitative outcome measurement in subacute and chronic trauma care after SCI. Methods: Here, I revisit the main findings of two comprehensive scoping reviews recently published by our team on this topic. I offer a perspective on the combined findings of these scoping reviews, which integrate the changes in sEMG with SCI and the use of sEMG in neurorehabilitation after SCI. Results: sEMG provides a complimentary assessment to quantify the residual control of muscles with great sensitivity and detail compared to the traditional clinical assessments. Our scoping reviews unveiled the ability of the sEMG assessment to detect discomplete lesions (muscles with absent motor scores but present sEMG). Moreover, sEMG is able to measure the spontaneous activity of motor units at rest, and during passive maneuvers, the evoked responses with sensory or motor stimulation, and the integrity of the spinal cord and descending tracts with motor evoked potentials. This greatly complements the diagnostics of the SCI in the subacute phase of trauma care and deepens our understanding of neurorehabilitation strategies during the chronic phase of the traumatic injury. Conclusions: sEMG offers important insights into the neurophysiological factors underlying sensorimotor impairment and recovery after SCIs. Although several qualitative or semi-quantitative outcome measures determine the level of injury and the natural recovery after SCIs, using quantitative measures such as sEMG is promising. Nonetheless, there are still several barriers limiting the use of sEMG in the clinical environment and a need to advance high-density sEMG technology.

Optimizing nerve transfer surgery in tetraplegia: clinical decision making based on innervation patterns in spinal cord injury

OBJECTIVE

Nerve transfers are increasingly being utilized in the treatment of chronic tetraplegia, with increasing literature describing significant improvements in sensorimotor function up to years after injury. However, despite technical advances, clinical outcomes remain heterogenous. Preoperative electrodiagnostic testing is the most direct measure of nerve health and may provide prognostic information that can optimize preoperative patient selection. The objective of this study in patients with spinal cord injury (SCI) was to determine various zones of injury (ZOIs) via electrodiagnostic assessment (EDX) to predict motor outcomes after nerve transfers in tetraplegia.

METHODS

This retrospective review of prospectively collected data included all patients with tetraplegia from cervical SCI who underwent nerve transfer at the authors' institution between 2013 and 2020. Preoperative demographic data, results of EDX, operative details, and postoperative motor outcomes were extracted. EDX was standardized into grades that describe donor and recipient nerves. Five zones of SCI were defined. Motor outcomes were then compared based on various zones of innervation.

RESULTS

Nineteen tetraplegic patients were identified who underwent 52 nerve transfers targeting hand function, and 75% of these nerve transfers were performed more than 1 year postinjury, with a median interval to surgery following SCI of 24 (range 8-142) months. Normal recipient compound muscle action potential and isolated upper motor neuron injury on electromyography (EMG) were associated with greater motor recovery. When nerve transfers were stratified based on donor EMG, greater motor gains were associated with normal than with abnormal donor EMG motor unit recruitment patterns. When nerve transfers were separated based on donor and recipient nerves, normal flexor donors were more crucial than normal extensor donors in powering their respective flexor recipients.

CONCLUSIONS

This study elucidates the relationship of the preoperative innervation zones in SCI patients to final motor outcomes. EDX studies can be used to tailor surgical therapies for nerve transfers in patients with tetraplegia. The authors propose an algorithm for optimizing nerve transfer strategies in tetraplegia, whereby understanding the ZOI and grade of the donor/recipient nerve is critical to predicting motor outcomes.

Supinator to Posterior Interosseous Nerve Transfer for Restoration of Finger Extension

BACKGROUND

Cervical spinal cord injuries result in a severe loss of function and independence. The primary goal for these patients is the restoration of hand function. Nerve transfers have recently become a powerful intervention to restore the ability to grasp and release objects. The supinator muscle, although a suboptimal tendon transfer donor, serves as an ideal distal nerve donor for reconstructive strategies of the hand. This transfer is also applicable to lower brachial plexus injuries.

OBJECTIVE

To describe the supinator to posterior interosseous nerve transfer with the goal of restoring finger extension following spinal cord or lower brachial plexus injury.

METHODS

Nerve branches to the supinator muscle are transferred to the posterior interosseous nerve supplying the finger extensor muscles in the forearm.

RESULTS

The supinator to posterior interosseous nerve transfer is effective in restoring finger extension following spinal cord or lower brachial plexus injury.

CONCLUSION

This procedure represents an optimal nerve transfer as the donor nerve is adjacent to the target nerve and its associated muscles. The supinator muscle is innervated by the C5-6 nerve roots and is often available in cases of cervical SCI and injuries of the lower brachial plexus. Additionally, supination function is retained by supination action of the biceps muscle.

Role of electrodiagnosis in nerve transfers for focal neuropathies and brachial plexopathies

Over the past 2 decades, the surgical treatment of brachial plexus and peripheral nerve injuries has advanced considerably. Nerve transfers have become an important surgical tool in addition to nerve repair and grafting. Electrodiagnosis has traditionally played a role in the diagnosis and localization of peripheral nervous system injuries, but a different approach is needed for surgical decision-making and monitoring recovery. When patients have complete or severe injuries they should be referred to surgical colleagues early after injury, as outcomes are best when nerve transfers are performed within the first 3 to 6 mo after onset. Patients with minimal recovery of voluntary activity are particularly challenging, and the presence of a few motor unit action potentials in these individuals should be interpreted on the basis of timing and evidence of ongoing reinnervation. Evaluation of potential recipient and donor muscles, as well as redundant muscles, for nerve transfers requires an individualized approach to optimize the chances of a successful surgical intervention. Anomalous innervation takes on new importance in these patients. Communication between surgeons and electrodiagnostic medicine specialists (EMSs) is best facilitated by a joint collaborative clinic. Ongoing monitoring of recovery post-operatively is critical to allow for decision making for continued surgical and rehabilitation treatments. Different electrodiagnostic findings are expected with resolution of neurapraxia, distal axon sprouting, and axonal regrowth. As new surgical techniques become available, EMSs will play an important role in the assessment and treatment of these patients with severe nerve injuries.

The accuracy of needle electrode placement by trainees in selected forearm muscles using verification by neuromuscular ultrasound

INTRODUCTION

Anatomic landmarks alone may not always be sufficient to accurately guide electromyography (EMG) electrode needle placement.

METHODS

Senior residents and fellows (n = 11) targeted 4 forearm muscles with anatomic landmarks alone versus with audiovisual EMG feedback. Accuracy of EMG needle placement was verified using neuromuscular ultrasound imaging.

RESULTS

While relatively large and superficial FCR muscle was sampled at a rate of 100% with and without audiovisual EMG feedback, accuracy of deeper and/or smaller forearm muscles (FPL, EIP, and SUP) diminished significantly without audiovisual EMG feedback.

DISCUSSION

Our study suggests that in clinical scenarios in which an electrodiagnostician relies on anatomic landmarks alone to target small and deep muscles, the risk of misplacement of needle electrode is increased. Consideration for neuromuscular ultrasound to augment training and/or real time guidance in EMG practice may be appropriate.

Properties of the surface electromyogram following traumatic spinal cord injury: a scoping review

Traumatic spinal cord injury (SCI) disrupts spinal and supraspinal pathways, and this process is reflected in changes in surface electromyography (sEMG). sEMG is an informative complement to current clinical testing and can capture the residual motor command in great detail-including in muscles below the level of injury with seemingly absent motor activities. In this comprehensive review, we sought to describe how the sEMG properties are changed after SCI. We conducted a systematic literature search followed by a narrative review focusing on sEMG analysis techniques and signal properties post-SCI. We found that early reports were mostly focused on the qualitative analysis of sEMG patterns and evolved to semi-quantitative scores and a more detailed amplitude-based quantification. Nonetheless, recent studies are still constrained to an amplitude-based analysis of the sEMG, and there are opportunities to more broadly characterize the time- and frequency-domain properties of the signal as well as to take fuller advantage of high-density EMG techniques. We recommend the incorporation of a broader range of signal properties into the neurophysiological assessment post-SCI and the development of a greater understanding of the relation between these sEMG properties and underlying physiology. Enhanced sEMG analysis could contribute to a more complete description of the effects of SCI on upper and lower motor neuron function and their interactions, and also assist in understanding the mechanisms of change following neuromodulation or exercise therapy.

Motor unit number index detects the effectiveness of surgical treatment in improving distal motor neuron loss in patients with incomplete cervical spinal cord injury

BACKGROUND

Recovery of motor dysfunction is important for patients with incomplete cervical spinal cord injury (SCI). To enhance the recovery of muscle strength, both research and treatments mainly focus on injury of upper motor neurons at the direct injury site. However, accumulating evidences have suggested that SCI has a downstream effect on the peripheral nervous system, which may contribute to the poor improvement of the muscle strength after operation. The aim of this study is to investigate the impact of early vs. delayed surgical intervention on the lower motor neurons (LMNs) distal to the injury site in patients with incomplete cervical SCI.

METHODS

Motor unit number index (MUNIX) was performed on the tibialis anterior (TA), extensor digitorum brevis (EDB) and abductor hallucis (AH) in 47 patients with incomplete cervical SCI (early vs. delayed surgical-treatment: 17 vs. 30) and 34 healthy subjects approximately 12 months after operation. All patients were further assessed by American spinal injury association (ASIA) motor scales and Medical Research Council (MRC) scales.

RESULTS

There are no difference of both ASIA motor scores and MRC scales between the patients who accepted early and delayed surgical treatment (P > 0.05). In contrast, the patients undergoing early surgical treatment showed lower MUSIX values in both bilateral EDB and bilateral TA, along with greater MUNIX values in both right-side EDB and right-side TA, compared to the patients who accepted delayed surgical treatment (P < 0.05).

CONCLUSIONS

Cervical SCI has a negative effect on the LMNs distal to the injury site. Early surgical intervention in Cervical SCI patients may improve the dysfunction of LMNs distal to the injury site, reducing secondary motor neuron loss, and eventually improving clinical prognosis.

Combined nerve and tendon transfer to restore elbow extension in tetraplegic patients: surgical technique and case report

INTRODUCTION

In individuals with tetraplegia, elbow extension is critical for overhead activities, weight shifting, independent transfers, and to perform self-care tasks such as eating. At present, restoration of elbow extension in tetraplegic patients can be performed using either tendon or nerve transfers. Each procedure presents several advantages and limitations that must be discussed with the potential surgical candidate, based on remaining muscular functions and functional goals.

CASE PRESENTATION

We propose a novel combined technique of both tendon and nerve transfer to restore active elbow extension by transferring the posterior deltoid tendon to the triceps tendon and the branch of teres minor nerve to the long head of the triceps nerve. Techniques were performed from the same shoulder posterior surgical approach.

DISCUSSION

This surgical technique can add the benefits of each tendon and nerve transfer, leading to a reduction of failure rates, with more predictable outcomes.

Nerve transfers in the upper extremity following cervical spinal cord injury. Part 1: Systematic review of the literature

OBJECTIVE

Patients with cervical spinal cord injury (SCI)/tetraplegia consistently rank restoring arm and hand function as their top functional priority to improve quality of life. Motor nerve transfers traditionally used to treat peripheral nerve injuries are increasingly being used to treat patients with cervical SCIs. In this study, the authors performed a systematic review summarizing the published literature on nerve transfers to restore upper-extremity function in tetraplegia.

METHODS

A systematic literature search was conducted using Ovid MEDLINE 1946-, Embase 1947-, Scopus 1960-, Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews, and clinicaltrials.gov to identify relevant literature published through January 2019. The authors included studies that provided original patient-level data and extracted information on clinical characteristics, operative details, and strength outcomes after nerve transfer procedures. Critical review and synthesis of the articles were performed.

RESULTS

Twenty-two unique studies, reporting on 158 nerve transfers in 118 upper limbs of 92 patients (87 males, 94.6%) were included in the systematic review. The mean duration from SCI to nerve transfer surgery was 18.7 months (range 4 months-13 years) and mean postoperative follow-up duration was 19.5 months (range 1 month-4 years). The main goals of reinnervation were the restoration of thumb and finger flexion, elbow extension, and wrist and finger extension. Significant heterogeneity in transfer strategy and postoperative outcomes were noted among the reports. All but one case report demonstrated recovery of at least Medical Research Council grade 3/5 strength in recipient muscle groups; however, there was greater variation in the results of larger case series. The best, most consistent outcomes were demonstrated for restoration of wrist/finger extension and elbow extension.

CONCLUSIONS

Motor nerve transfers are a promising treatment option to restore upper-extremity function after SCI. Flexor reinnervation strategies show variable treatment effect sizes; however, extensor reinnervation may provide more consistent, meaningful recovery. Despite numerous published case reports describing good patient outcomes with nerve transfers, there remains a paucity in the literature regarding optimal timing and long-term clinical outcomes with these procedures.

Case Report: Double Oberlin Nerve Transfer to Restore Elbow Flexion Following C5-C6 Avulsion Injury

BACKGROUND AND IMPORTANCE

The use of nerve transfers to restore nerve function following traumatic avulsion injuries has been described, though there is still a paucity in the literature documenting technique and long-term outcomes for these procedures. The double Oberlin nerve transfer involves transferring fascicles from the median and ulnar nerves to the musculocutaneous nerve to restore elbow flexion in patients with a C5-C6 avulsion injury. The purpose of this case report is to present our indications and technique for a double Oberlin transfer in addition to exhibiting video footage at follow-up time points documenting the incremental improvement in elbow flexion following the injury.

CLINICAL PRESENTATION

The patient is a 25-yr old, left-hand dominant male who presented 5 mo following a motor vehicle accident. He had 0/5 biceps muscle strength on the left with a computed tomography myelogram that demonstrated pseudomeningoceles from C2-C3 to C7-T1 with root avulsions of C5 and C6. He was subsequently indicated for a double Oberlin nerve transfer to restore elbow flexion.

CONCLUSION

In this case report, we present our technique and outcomes for a double Oberlin transfer with restoration of elbow flexion at 1-yr follow-up for a patient with traumatic brachial plexus injury. We believe that the double Oberlin transfer serves as a safe and effective method to restore elbow flexion in this patient population.