Reverse end-to-side nerve transfer: from animal model to clinical use

Current perspectives on peripheral nerve repair and management of the nerve gap

From the first surgical repair of a nerve in the 6th century, progress in the field of peripheral nerve surgery has marched on; at first slowly but today at great pace. Whether performing primary neurorrhaphy or managing multiple large nerve defects, the modern nerve surgeon has an extensive range of tools, techniques and choices available to them. Continuous innovation in surgical equipment and technique has enabled the maturation of autografting as a gold standard for reconstruction and welcomed the era of nerve transfer techniques all while bioengineers have continued to add to our armamentarium with implantable devices, such as conduits and acellular allografts. We provide the reader a concise and up-to-date summary of the techniques available to them, and the evidence base for their use when managing nerve transection including current use and applicability of nerve transfer procedures.

Supercharge end-to-side nerve transfer from anterior interosseous nerve to augment intrinsic recovery in high ulnar nerve injuries of varying magnitudes

BACKGROUND

High ulnar nerve injuries result in intrinsic muscle weakness and are inconvenient for patients. Moreover, conventional surgical techniques often fail to achieve satisfactory motor recovery. A potential reconstructive solution in the form of the supercharge end-to-side (SETS) anterior interosseous nerve (AIN) transfer method has emerged. Therefore, this study aims to compare surgical outcomes of patients with transected and in-continuity high ulnar nerve lesions following SETS AIN transfer.

METHODS

Between June 2015 and May 2023, patients with high ulnar palsy in the form of transection injuries or lesion-in-continuity were recruited. The assessment encompassed several objective results, including grip strength, key pinch strength, compound muscle action potential, sensory nerve action potential, and two-point discrimination tests. The muscle power of finger abduction and adduction was also recorded. Additionally, subjective questionnaires were utilized to collect data on patient-reported outcomes. Overall, the patients were followed up for up to 2 years.

RESULTS

Patients with transected high ulnar nerve lesions exhibited worse baseline performance than those with lesion-in-continuity, including motor and sensory functions. However, they experienced greater motor improvement but less sensory recovery, resulting in comparable final motor outcomes in both groups. In contrast, the transection group showed worse sensory outcomes.

CONCLUSIONS

Our findings suggest that SETS AIN transfer benefits patients with high ulnar nerve palsy, regardless of the lesion type. Nonetheless, improvements may be more pronounced in patients with transected lesions.

Supercharging of the ulnar nerve: clinical and neurophysiological assessment at 2 years for nine proximal injuries

LEVEL OF EVIDENCE

II.

Assessment, patient selection, and rehabilitation of nerve transfers

Peripheral nerve injuries are common and can have a devastating effect on physical, psychological, and socioeconomic wellbeing. Peripheral nerve transfers have become the standard of care for many types of peripheral nerve injury due to their superior outcomes relative to conventional techniques. As the indications for, and use of, nerve transfers expand, the importance of pre-operative assessment and post-operative optimization increases. There are two principal advantages of nerve transfers: (1) their ability to shorten the time to reinnervation of muscles undergoing denervation because of peripheral nerve injury; and (2) their specificity in ensuring proximal motor and sensory axons are directed towards appropriate motor and sensory targets. Compared to conventional nerve grafting, nerve transfers offer opportunities to reinnervate muscles affected by cervical spinal cord injury and to augment natural reinnervation potential for very proximal injuries. This article provides a narrative review of the current scientific knowledge and clinical understanding of nerve transfers including peripheral nerve injury assessment and pre- and post-operative electrodiagnostic testing, adjuvant therapies, and post-operative rehabilitation for optimizing nerve transfer outcomes.

A Surgical Framework for the Management of Incomplete Axillary Nerve Injuries

BACKGROUND

 Axillary nerve injury is the most common nerve injury affecting shoulder function. Nerve repair, grafting, and/or end-to-end nerve transfers are used to reconstruct complete neurotmetic axillary nerve injuries. While many incomplete axillary nerve injuries self-resolve, axonotmetic injuries are unpredictable, and incomplete recovery occurs. Similarly, recovery may be further inhibited by superimposed compression neuropathy at the quadrangular space. The current framework for managing incomplete axillary injuries typically does not include surgery.

METHODS

 This study is a retrospective analysis of 23 consecutive patients with incomplete axillary nerve palsy who underwent quadrangular space decompression with additional selective medial triceps to axillary end-to-side nerve transfers in 7 patients between 2015 and 2019. Primary outcome variables included the proportion of patients with shoulder abduction M3 or greater as measured on the Medical Research Council (MRC) scale, and shoulder pain measured on a Visual Analogue Scale (VAS). Secondary outcome variables included pre- and postoperative Disabilities of the Arm, Shoulder, and Hand Questionnaire (DASH) scores.

RESULTS

 A total of 23 patients met the inclusion criteria and underwent nerve surgery a mean 10.7 months after injury. Nineteen (83%) patients achieved MRC grade 3 shoulder abduction or greater after intervention, compared with only 4 (17%) patients preoperatively (p = 0.001). There was a significant decrease in VAS shoulder pain scores of 4.2 ± 2.5 preoperatively to 1.9 ± 2.4 postoperatively (p < 0.001). The DASH scores also decreased significantly from 48.8 ± 19.0 preoperatively to 30.7 ± 20.4 postoperatively (p < 0.001). Total follow-up was 17.3 ± 4.3 months.

CONCLUSION

 A surgical framework is presented for the appropriate diagnosis and surgical management of incomplete axillary nerve injury. Quadrangular space decompression with or without selective medial triceps to axillary end-to-side nerve transfers is associated with improvement in shoulder abduction strength, pain, and DASH scores in patients with incomplete axillary nerve palsy.

Perineurial Window is Critical for Experimental Reverse End-to-Side Nerve Transfer

BACKGROUND

The depth of connective tissue window in the side of a recipient nerve in reverse end-to-side transfers (RETS) remains controversial.

OBJECTIVE

To test whether the depth of connective tissue disruption influences the efficiency of donor axonal regeneration in the context of RETS.

METHODS

Sprague-Dawley rats (n = 24) were assigned to 1 of the 3 groups for obturator nerve to motor femoral nerve RETS: group 1, without epineurium opening; group 2, with epineurium only opening; and group 3, with epineurium and perineurium opening. Triple retrograde labeling was used to assess the number of motor neurons that had regenerated into the recipient motor femoral branch. Thy1-GFP rats (n = 8) were also used to visualize the regeneration pathways in the nerve transfer networks at 2- and 8-week time point using light sheet fluorescence microscopy.

RESULTS

The number of retrogradely labeled motor neurons that had regenerated distally toward the target muscle was significantly higher in group 3 than that in groups 1 and 2. Immunohistochemistry validated the degree of connective tissue disruption among the 3 groups, and optical tissue clearing methods demonstrated donor axons traveling outside the fascicles in groups 1 and 2 but mostly within the fascicles in group 3.

CONCLUSION

Creating a perineurial window in the side of recipient nerves provides the best chances of robust donor axonal regeneration across the RETS repair site. This finding aids nerve surgeons by confirming that a deep window should be undertaken when doing a RETS procedure.

Primary Repair versus Reverse End-to-Side Coaptation by Anterior Interosseous Nerve Transfer in Proximal Ulnar Nerve Injuries

BACKGROUND

Proximal ulnar nerve lacerations are challenging to treat because of the complex integration of sensory and motor function in the hand. The purpose of this study was to compare primary repair and primary repair plus anterior interosseous nerve (AIN) reverse end-to-side (RETS) coaptation in the setting of proximal ulnar nerve injuries.

METHODS

A prospective cohort study was performed of all patients at a single, academic, level I trauma center from 2014 to 2018 presenting with isolated complete ulnar nerve lacerations. Patients underwent either primary repair (PR) only or primary repair and AIN RETS (PR + RETS). Data collected included demographic information; quick Disabilities of the Arm, Shoulder and Hand questionnaire score; Medical Research Council score; grip and pinch strength; and visual analogue scale pain scores at 6 and 12 months postoperatively.

RESULTS

Sixty patients were included in the study: 28 in the PR group and 32 in the RETS + PR group. There was no difference in demographic variables or location of injury between the two groups. Average quick Disabilities of the Arm, Shoulder and Hand questionnaire scores for the PR and PR + RETS groups were 65 ± 6 and 36 ± 4 at 6 months and 46 ± 4 and 24 ± 3 at 12 months postoperatively, respectively, and were significantly lower in the PR + RETS group at both points. Average grip and pinch strength were significantly greater for the PR + RETS group at 6 and 12 months.

CONCLUSION

This study demonstrated that primary repair of proximal ulnar nerve injuries plus AIN RETS coaptation yielded superior strength and improved upper extremity function when compared with PR alone.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, II.

End-to-Side vs. Free Graft Nerve Reconstruction-Experimental Study on Rats

The long history of regeneration nerve research indicates many clinical problems with surgical reconstruction to be resolved. One of the promising surgical techniques in specific clinical conditions is end-to-side neurorrhaphy (ETS), described and then repeated with different efficiency in the 1990s of the twentieth century. There are no reliable data on the quality of recipient nerve regeneration, possible donor nerve damage, and epineural window technique necessary to be performed. This research attempts to evaluate the possible regeneration after end-to-side neurorrhaphy, its quality, potential donor nerve damage, and the influence of epineural windows on regeneration efficiency. Forty-five female Wistar rats were divided into three equal groups, and various surgical technics were applied: A-ETS without epineural window, B-ETS with epineural window, and C-free graft reconstruction. The right peroneal nerve was operated on, and the tibial nerve was selected as a donor. After 24 weeks, the regeneration was evaluated by (1) footprint analysis every two weeks with PFI (peroneal nerve function index), TFI (tibial nerve function index), and SFI (sciatic nerve function index) calculations; (2) the amplitude and latency measurements of motor evoked potentials parameters recorded on both sides of the peroneal and tibial nerves when electroneurography with direct sciatic nerve electrical stimulation and indirect magnetic stimulation were applied; (3) histomorphometry with digital conversion of a transverse semithin nerve section, with axon count, fibers diameter, and calculation of axon area with a semiautomated method were performed. There was no statistically significant difference between the groups investigated in all the parameters. The functional indexes stabilized after eight weeks (PFI) and six weeks (TFI and SFI) and were positively time related. The lower amplitude of tibial nerve potential in groups A and B was proven compared to the non-operated side. Neurophysiological parameters of the peroneal nerve did not differ significantly. Histomorphometry revealed significantly lower diameter and area of axons in operated peroneal nerves compared to non-operated nerves. The axon count was at a normal level in every group. Tibial nerve parameters did not differ from non-operated values. Regeneration of the peroneal nerve after ETS was ascertained to be at the same level as in the case of free graft reconstruction. Peroneal nerves after ETS and free graft reconstruction were ascertained to have a lower diameter and area than non-operated ones. The technique of an epineural window does not influence the regeneration result of the peroneal nerve. The tibial nerve motor evoked potentials were characterized by lower amplitudes in ETS groups, which could indicate axonal impairment.

Reverse End-to-Side Transfer to Ulnar Motor Nerve: Evidence From Preclinical and Clinical Studies

The disappointing outcomes of conventional nerve repair or grafting procedures for proximal ulnar nerve injuries have led the scientific community to search for better alternatives. The pronator quadratus branch of the anterior interosseous nerve has been transferred to the distal ulnar motor branch in a reverse end-to-side fashion with encouraging results. This transfer is now becoming commonly used as an adjunct to cubital tunnel decompression in patients with compressive ulnar neuropathy, underscoring the need for this knowledge transfer to the neurosurgical community. However, the mechanism of recovery after these transfers is not understood completely. We have reviewed the existing preclinical and clinical literature relevant to this transfer to summarize the current level of understanding of the underlying mechanisms, define the indications for performing this transfer in the clinic, and identify the complications and best practices with respect to the operative technique. We have also attempted to identify the major deficiencies in our current level of understanding of the recovery process to propose directions for future research.

Beyond the Cubital Tunnel: Use of Adjunctive Procedures in the Management of Cubital Tunnel Syndrome

BACKGROUND

Our management of cubital tunnel syndrome has expanded to involve multiple adjunctive procedures, including supercharged end-to-side anterior interosseous to ulnar nerve transfer, cross-palm nerve grafts from the median to ulnar nerve, and profundus tenodesis. We also perform intraoperative brief electrical stimulation in patients with severe disease. The aims of this study were to evaluate the impact of adjunctive procedures and electrical stimulation on patient outcomes.

METHODS

We performed a retrospective review of 136 patients with cubital tunnel syndrome who underwent operative management from 2013 to 2018. A total of 38 patients underwent adjunctive procedure(s), and 33 received electrical stimulation. A historical cohort of patients who underwent cubital tunnel surgery from 2009 to 2011 (n = 87) was used to evaluate the impact of adjunctive procedures. Study outcomes were postoperative improvements in Disabilities of the Arm, Shoulder, and Hand (DASH) questionnaire scores, pinch strength, and patient-reported pain and quality of life.

RESULTS

In propensity score-matched samples, patients who underwent adjunctive procedures had an 11.3-point greater improvement in DASH scores than their matched controls (P = .0342). In addition, patients who received electrical stimulation had significantly improved DASH scores relative to baseline (11.7-point improvement, P < .0001), whereas their control group did not. However, when compared between treatment arms, there were no significant differences for any study outcome.

CONCLUSIONS

Patients who underwent adjunctive procedures experienced greater improvement in postoperative DASH scores than their matched pairs. Additional studies are needed to evaluate the effects of brief electrical stimulation in compression neuropathy.

Molecular Basis of Surgical Coaptation Techniques in Peripheral Nerve Injuries

Peripheral nerve injuries requiring surgical repair affect over 100,000 individuals in the US annually. Three accepted methods of peripheral repair include end-to-end, end-to-side, and side-to-side neurorrhaphy, each with its own set of indications. While it remains important to understand the specific circumstances in which each method is employed, a deeper understanding of the molecular mechanisms underlying the repair can add to the surgeon's decision-making algorithm when considering each technique, as well as help decide nuances in technique such as the need for making epineurial versus perineurial windows, length and dept of the nerve window, and distance from target muscle. In addition, a thorough knowledge of individual factors that are active in a particular repair can help guide research into adjunct therapies. This paper serves to summarize the similarities and divergences of the three commonly used nerve repair strategies and the scope of molecular mechanisms and signal transduction pathways in nerve regeneration as well as to identify the gaps in knowledge that should be addressed if we are to improve clinical outcomes in our patients.

Reverse End-to-Side Nerve Transfer for Severe Ulnar Nerve Injury: A Western Canadian Multicentre Prospective Nonrandomized Cohort Study

BACKGROUND

Reverse end-to-side (RETS) nerve transfer has become increasingly popular in patients with severe high ulnar nerve injury, but the reported outcomes have been inconsistent.

OBJECTIVE

To evaluate the "babysitting effect," we compared outcomes after anterior interosseous nerve RETS transfer with nerve decompression alone. To evaluate the source of regenerating axons, a group with end-to-end (ETE) transfer was used for comparisons.

METHODS

Electrophysiology measures were used to quantify the regeneration of anterior interosseous nerve (AIN) and ulnar nerve fibers while functional recovery was evaluated using key pinch and Semmes-Weinstein monofilaments. The subjects were followed postsurgically for 3 years.

RESULTS

Sixty-two subjects (RETS = 25, ETE = 16, and decompression = 21) from 4 centers in Western Canada were enrolled. All subjects with severe ulnar nerve injury had nerve compression at the elbow except 10 in the ETE group had nerve laceration or traction injury. Postsurgically, no reinnervation from the AIN to the abductor digiti minimi muscles was seen in any of the RETS subjects. Although there was no significant improvement in compound muscle action potentials amplitudes and pressure detection thresholds in the decompression and RETS group, key pinch strength significantly improved in the RETS group ( P < .05).

CONCLUSION

The results from published clinical trials are conflicting in part because crossover regeneration from the donor nerve has never been measured. Unlike those with ETE nerve transfers, we found that there was no crossover regeneration in the RETS group. The extent of reinnervation was also no different from decompression surgery alone. Based on these findings, the justifications for this surgical technique need to be carefully re-evaluated.

Reverse End-to-Side (Supercharging) Nerve Transfer: Conceptualization, Validation, and Translation

Partial nerve recovery either after expectant observation following an injury in-continuity or after nerve repair is not an uncommon occurrence. Historically, treatment strategies in these situations-late repair, revision repair, or acceptance of a mediocre result-were unsatisfying. The reverse end-to-side, or supercharging, nerve transfer was conceived to offer a more palatable option. Partially validated primarily through small animal research, supercharging has been rapidly translated to clinical practice. Many have extended the indications beyond the original intent, though the final place of this technique in the peripheral nerve surgeon's armamentarium is still yet to be determined.

Evaluation of functional recovery in the intrinsic and flexor muscles after nerve transfer for ulnar nerve lesion. A new measurement method: The Cha method

"Supercharge" end-to-side (SETS) nerve transfer for lesions of the proximal ulnar nerve is a recognized novel option, but improvement in motor function after surgery has not been properly evaluated. We therefore propose a modified method for quantitative evaluation of improvement in the intrinsic hand strength. We screened 216 patients with proximal ulnar nerve lesions who presented to our outpatient department from 2012 to 2020. Of these, 101 met our inclusion/exclusion criteria and were evaluated just before surgery. We used a novel method to measure finger abduction ("2nd-abd"), adduction ("5th-add"), and ring and little finger flexion strength ("4,5 grip"), and analyzed correlations with established pinch strength data. The male:female sex ratio was 86:15, and the ratio dominant to nondominant arm involvement was 68:33. All strength measurements were analyzed as percentage affected to contralateral normal side. On Pearson correlation analysis, the strength ratios for "4,5 grip", "2nd-abd", and "5th-add", but not "5 fingers (total) grip", showed significant positive correlation with key and oppositional pinch strength (all p &lt; 0.001). Additionally, linear regression analysis showed identical results for each strength correlation with key/oppositional pinch, except for "5 fingers total) grip" (all, p &lt; 0.001). SETS is a reasonable alternative for lesions of the proximal ulnar nerve. The measurement method we propose is feasible for specific assessment of intrinsic muscle strength, which improves after surgery. LEVEL OF EVIDENCE: Diagnostic, level IV.

Contemporary Approaches to Peripheral Nerve Surgery

“State of the Art” Learning Objectives: This manuscript serves to provide the reader with a general overview of the contemporary approaches to peripheral nerve reconstruction as the field has undergone considerable advancement over the last 3 decades. The learning objectives are as follows: To provide the reader with a brief history of peripheral nerve surgery and some of the landmark developments that allow for current peripheral nerve care practices. To outline the considerations and management options for the care of patients with brachial plexopathy, spinal cord injury, and lower extremity peripheral nerve injury. Highlight contemporary surgical techniques to address terminal neuroma and phantom limb pain. Review progressive and future procedures in peripheral nerve care, such as supercharge end-to-side nerve transfers. Discuss rehabilitation techniques for peripheral nerve care.

Anterior Interosseous-to-Ulnar Motor Nerve Transfers: A Single Center's Experience in Restoring Intrinsic Hand Function

Background: Transfer of the anterior interosseous nerve (AIN) into the ulnar motor branch improves intrinsic hand function in patients with high ulnar nerve injuries. We report our outcomes of this nerve transfer and hypothesize that any improvement in intrinsic hand function is beneficial to patients. Methods: A retrospective review of all AIN-to-ulnar motor nerve transfers, including both supercharged end-to-side (SETS) and end-to-end (ETE) transfers, from 2011 to 2018 performed by 2 surgeons was conducted. All adult patients who underwent this nerve transfer for any reason with greater than 6 months' follow-up and completed charts were included. Primary outcome measures were motor function using the British Medical Research Council (BMRC) grading system and subjective satisfaction with surgery using a visual analog scale. Secondary outcome measures included complications and donor site deficits. Results: Of the 57 patients who underwent nerve transfer, 32 patients met the inclusion criteria. The average follow-up and average time to surgery were 12 and 15.6 months, respectively. The overall average BMRC score was 2.9/5, with a trend toward better recovery in patients who received earlier surgery (<12 months = BMRC 3.7, ≥12 months = BMRC 2.2; P < .01). Patients with an SETS transfer had better results that those with an ETE transfer (SETS = 3.2, ETE = 2.6). There were no donor deficits after operation. One patient developed complex regional pain syndrome. Conclusions: Patients with earlier surgery and an in-continuity nerve (receiving an SETS transfer) showed improved recovery with a higher BMRC grade compared with those who underwent later surgery. Any improvements in intrinsic hand function would be beneficial to patients.

Surgical Treatment of Foot Drop: Patient Evaluation and Peripheral Nerve Treatment Options

Foot drop is a common clinical condition which may substantially impact physical function and health-related quality of life. The etiologies of foot drop are diverse and a detailed history and physical examination are essential in understanding the underlying pathophysiology and capacity for spontaneous recovery. Patients presenting with acute foot drop or those without significant spontaneous recovery of motor deficits may be candidates for surgical intervention. The timing, mechanism, and severity of neural injury resulting in foot drop influence the selection of the most appropriate peripheral nerve surgery, which may include direct nerve repair, neurolysis, nerve grafting, or nerve transfer.

Sensory Neurotization of the Ulnar Nerve, Surgical Techniques and Functional Outcomes: A Review

When ulnar nerve lesions happen above the wrist level, sensation recovery after acute repair or nerve grafting is often challenging. Distal sensory nerve transfers may be an option for overcoming these sequelae. However, little data has been published on this topic. This study aims to review the surgical procedures currently proposed, along with their functional results. Six donor nerves have been described at the wrist level: the palmar branch of the median nerve, the cutaneous branch of the median nerve to the palm with or without fascicles of the ulnar digital nerve of the index finger, the posterior interosseous nerve, the third palmar digital nerve, the radial branch of the superficial radial nerve, the median nerve, and the fascicule for the third web space. Three donor nerves have been reported at the hand level: the ulnar digital nerves of the index, and the radial or ulnar digital nerves of the long finger. Three target sites were used: the superficial branch of the ulnar nerve, the dorsal branch of the ulnar nerve, and the ulnar digital branch of the fifth digit. All the technical points have been illustrated with anatomical dissection pictures. After assessing sensory recovery using the British Medical Research Council scale, a majority of excellent recoveries scaled S3+ or S4 have been reported in the targeted territory for each technique.

Anterior Interosseous Nerve to Ulnar Nerve Transfer: A systematic review

Background

Objectives

Methods

Results

Conclusion

Surgical Innovations to Restore Function in Pediatric Peripheral Nerve Conditions

Peripheral nerve injuries in children can result in devastating lifelong deficits. Because of the time-sensitive nature of muscle viability and the limited speed of nerve regeneration, early recognition and treatment of nerve injuries are essential to restore function. Innovative surgical techniques have been developed to combat the regenerative length and speed; these include nerve transfers. Nerve transfers involve transferring a healthy, expendable donor nerve to an injured nerve to restore movement and sensation. Nerve transfers are frequently used to treat children affected by conditions, including UE trauma, brachial plexus birth injury, and acute flaccid myelitis. Pediatricians play an important role in the outcomes of children with these conditions through early diagnosis and timely referrals. With this review, we aim to provide awareness of state-of-the-art surgical treatment options that significantly improve the function of children with traumatic nerve injuries, brachial plexus birth injury, and acute flaccid myelitis.

Postoperative management and rehabilitation after the supercharged end-to-side anterior interosseous nerve to ulnar motor nerve transfer: A report of 3 cases

INTRODUCTION

Compressive ulnar neuropathy at the elbow is the second most common compressive neuropathy. Nerve transfers are used for severe ulnar neuropathies as a means of facilitating recovery. Hand therapy and rehabilitation after nerve transfers have not been extensively explored.

PURPOSE OF THE STUDY

The aim of this repeated case study was to describe the responses, functional outcome, and neuromuscular health of three participants after the supercharged end-to-side (SETS) anterior interosseous nerve (AIN) to ulnar motor nerve transfer do describe the hand therapy and recovery of 3 cases reflecting different recovery potential mediators, trajectories, and outcomes.

STUDY DESIGN

Repeated case study.

METHODS

Three participants of similar age (76-80 years) that had severe ulnar neuropathy who underwent surgical treatment including a SETS AIN to ulnar motor nerve surgery were purposively selected from an ongoing clinical trial, based on their response to the surgical and the rehabilitation intervention (large, moderate, and small improvements). Clinical evaluations included measuring range of motion, strength testing, and clinical tests (ie, Egawa's sign) and, subjective assessment of rehabilitation adherence., Quick Disability of Arm, Shoulder and Hand and decomposition-based quantitative electromyography were performed at >23 months to evaluate patients.

RESULTS

All the three participants completed the surgical and hand therapy interventions, demonstrating a variable course of recovery and functional outcomes. The Quick Disability of Arm, Shoulder and Hand scores (>23 months) for participants A, B, and C were 68, 30, and 18, respectively. The person with the least improvement had idiopathic Parkinson's disease, dyslipidemia, history of depression, and gout. Comparison across cases suggested that the comorbidities, longer time from neuropathy to the surgical intervention, and psychosocial barriers to exercise and rehabilitation adherence influenced the recovery process. The participants with the best outcomes demonstrated improvements in his lower motor neurons or motor unit counts (109 and 18 motor units in the abductor digiti minimi (ADM) and first dorsal interosseous, respectively) and motor unit stability (39.5% and 37.6% near-fiber jiggle in the ADM and first dorsal interosseous, respectively). The participant with moderate response to the interventions had a motor unit count of 93 for the ADM muscle. We were unable to determine motor unit counts and measurements from the participant with the poorest outcomes due to his physical limitations.

CONCLUSIONS

SETS AIN to ulnar motor nerve followed by multimodal hand therapy provides measurable improvements in neurophysiology and function, although engagement in hand therapy and outcomes appear to be mediated by comorbid physical and psychosocial health.

Ulnar nerve decompression and transposition with versus without supercharged end-to-side motor nerve transfer for advanced cubital tunnel syndrome: a randomized comparison study

OBJECTIVE

The objective of this prospective randomized study was to compare ulnar nerve decompression and anterior subfascial transposition with versus without supercharged end-to-side anterior interosseous nerve-to-ulnar motor nerve transfer for advanced cubital tunnel syndrome, to describe performing the nerve transfer through a small incision, and to investigate predictive factors for poor recovery following the procedure.

METHODS

Between January 2013 and October 2016, 93 patients were randomly allocated to a study group (n = 45) and a control group (n = 48). Patients in the study group were treated with supercharged motor nerve transfer via a 5-cm incision following decompression and anterior subfascial transposition. Patients in the control group were treated with decompression and anterior subfascial transposition alone. Postoperative pinch strength and compound muscle action potential amplitude (CMAPa) were assessed. Function of the limb was assessed based on the Gabel/Amadio scale. Between-group data were compared, and significance was set at p < 0.05. Potential risk factors were collected from demographic data and disease severity indicators.

RESULTS

At the final follow-up at 2 years, the results of the study group were superior to those of the control group with regard to postoperative pinch strength (75.13% ± 7.65% vs 62.11% ± 6.97%, p < 0.05); CMAPa of the first dorsal interossei (17.17 ± 5.84 mV vs 12.20 ± 4.09 mV, p < 0.01); CMAPa of abductor digiti minimi (11.57 ± 4.04 mV vs 8.43 ± 6.11 mV, p < 0.01); and excellent to good results (0.67 for the study group vs 0.35 for the control group, p < 0.05). Multivariate analysis showed that the advanced age (OR 2.98, 95% CI 2.25-4.10; p = 0.003) in the study group was related to unsatisfactory outcome in the patients.

CONCLUSIONS

In the treatment of advanced cubital tunnel syndrome, additional supercharged end-to-side anterior interosseous nerve-to-ulnar motor nerve transfer may produce a better function of the hand. The authors also found that cases in the elderly were related to unsatisfactory postoperative results for these patients and that they could be informed of the possibility of worsening surgery results.

Lower Extremity Nerve Transfers in Acute Flaccid Myelitis Patients: A Case Series

Acute flaccid myelitis (AFM) is characterized by flaccid paralysis following prodromal symptoms. Complete recovery is rare, and patients typically have residual extremity weakness. This study aimed to describe the technique and outcomes of lower extremity nerve transfers for children with AFM.

Current Concepts Review: Common Peroneal Nerve Palsy After Knee Dislocations

Dislocation of the native knee represents a challenging injury, further complicated by the high rate of concurrent injury to the common peroneal nerve (CPN). Initial management of this injury requires a thorough neurovascular examination, given the prevalence of popliteal artery injury and limb-threatening ischemia. Further management of a knee dislocation with associated CPN palsy requires coordinated care involving the sports surgeon for ligamentous knee reconstruction and the peripheral nerve surgeon for staged or concurrent peroneal nerve decompression and/or reconstruction. Finally, the foot and ankle surgeon is often required to manage a foot drop with a distal tendon transfer to restore foot dorsiflexion. For instance, the Bridle Procedure-a modification of the anterior transfer of the posterior tibialis muscle, under the extensor retinaculum, with tri-tendon anastomosis to the anterior tibial and peroneus longus tendons at the anterior ankle-can successfully return patients to brace-free ambulation and athletic function following CPN palsy. Cross-discipline coordination and collaboration is essential to ensure appropriate timing of operative interventions and ensure maintenance of passive dorsiflexion prior to tendon transfer.

Five Reliable Nerve Transfers for the Treatment of Isolated Upper Extremity Nerve Injuries

LEARNING OBJECTIVES

After studying this article and accompanying videos, the participant should be able to: 1. Understand and apply the principles of nerve transfer surgery for nerve injuries. 2. Discuss important considerations when performing nerve transfers, such as aspects of surgical technique and perioperative decision-making. 3. Understand indications for end-to-end versus supercharged reverse end-to-side nerve transfers. 4. Understand an algorithm for treating nerve injuries to include the indications and surgical techniques of five nerve transfers commonly performed for the treatment of isolated upper extremity nerve injuries. 5. Understand the outcomes and postoperative management of the discussed nerve transfers.

SUMMARY

Nerve transfers are gaining wide acceptance because of their superior results in the management of many nerve injuries of the upper extremity. This article presents five nerve transfers for the treatment of isolated nerve injuries in the authors' upper extremity nerve practice that offer reliable results. Indications, surgical techniques, outcomes, and postoperative management are reviewed. To maximize functional outcomes in patients with nerve injuries, the treatment should be individualized to the patient, and the principles for nerve transfers as described herein should be considered.

Supercharge End-to-Side Nerve Transfer: Systematic Review

Background: To decrease the time to reinnervation of the intrinsic motor end plates after high ulnar nerve injuries, a supercharged end-to-side (SETS) anterior interosseous to ulnar motor nerve transfer has been proposed. The purpose of this study was to compile and review the indications, outcomes, and complications of SETS anterior interosseous to ulnar motor nerve transfer. Methods: A literature search was performed, identifying 73 papers; 4 of which met inclusion and exclusion criteria, including 78 patients. Papers included were those that contained the results of SETS between the years 2000 and 2018. Data were pooled and analyzed focusing on the primary outcomes: intrinsic muscle recovery and complications. Results: Four studies with 78 patients met inclusion and exclusion criteria. Most patients (33.3%) underwent SETS for an ulnar nerve lesion in continuity, the average age was 46.5 years, and the average follow-up was 10 months. The average duration of symptoms before surgery was 99 weeks, all patients had weakness and numbness, nearly all (96%) had atrophy, and half (53%) had pain. Grip and key pinch strength improved 202% and 179%, respectively, from the preoperative assessment. The vast majority (91.9%) recovered intrinsic function at an average of 3.7 months. Other than 8% of patients who did not recover intrinsic strength, no other complications were reported in any of the 78 patients. Conclusions: The SETS is a successful procedure with low morbidity, which may restore intrinsic function in patients with proximal nerve injuries.

End-to-Side Anterior Interosseous Nerve Transfer: A Valuable Alternative for Traumatic High Ulnar Nerve Palsy

BACKGROUND

The prognosis of high ulnar nerve injury is poor despite nerve repair or grafting. Anterior interosseous nerve (AIN) transfers provide a satisfactory recovery. However, the efficacy of end-to-side (ETS) AIN transfer and optimal timing in Sunderland grade IV/V of high ulnar nerve injury is lacking.

OBJECTIVE

The goals were to compare the outcomes of high ulnar nerve injury managed with ETS AIN transfers with those managed with conventional procedures (nerve repair or graft only) and identify differences between early and delayed transfers.

METHODS

Patients with isolated high ulnar nerve injury (Sunderland grade IV/V) from 2010 to 2017 were recruited. Patients with conventional treatments and AIN transfers were designated as the control and AIN groups, respectively. Early transfer was defined as the AIN transfer performed within 8 weeks postinjury. Outcomes were measured and analyzed by the British Medical Research Council (BMRC) score, grip strength, and pinch strength.

RESULTS

A total of 24 patients with high ulnar nerve injury (Sunderland grade IV/V) were included. There were 11 and 13 patients in the control and AIN groups, respectively. In univariate analysis, both early and delayed AIN transfers demonstrated significantly better motor recovery among BMRC score and strength of grip and pinch at 12 months (P < 0.05). No statistical significance was found between early and delayed transfer. In multivariate analysis, both early and delayed transfers were regarded as strong and independent factors for motor recovery of ulnar nerve. Compared with the control, early [odds ratio (OR), 1.83; P < 0.001] and delayed (OR, 1.59; P < 0.001) transfers showed significant improvement with regard to BMRC scores. The pinch strength in early (OR, 31.68; P < 0.001) and delayed (OR, 26.45; P < 0.001) transfers was also significantly better.

CONCLUSION

The ETS AIN transfer, in either early or delayed fashion, significantly improved intrinsic motor recovery in high ulnar nerve injuries classified as Sunderland grade IV/V. The early transfer group demonstrated a trend toward better functional recovery with less downtime.

Nerve transfers in the upper extremity: A review

Injury of the brachial plexus and peripheral nerve often result in significant upper extremity dysfunction and disability. Nerve transfers are replacing other techniques as the gold standard for brachial plexus and other proximal peripheral nerve injuries. These transfers require an intimate knowledge of nerve topography, a technically demanding Intraneural dissection and require extensive physical therapy for retraining. In this review, we present a summary of the most widely accepted nerve transfers in the upper extremity described in the current literature.

Trends in Nerve Transfer Procedures Among Board-Eligible Orthopedic Hand Surgeons

Purpose

Enthusiasm for peripheral nerve transfers increased over the past several years, but further studies are still needed to establish the role of these procedures in peripheral nerve reconstruction. The primary goal of this study was to describe the frequency of nerve transfer surgery among newly trained orthopedic surgeons.

Methods

We queried the American Board of Orthopaedic Surgery Part II case log database for all nerve reconstruction Current Procedural Terminology codes for examination years 2004 to 2018 for surgeries performed between 2003 and 2017. Information collected for each patient included examination year, year of surgery, surgeon fellowship training subspecialty, geographic region (as defined by the American Board of Orthopaedic Surgery Part II case log database), patient age, and patient sex.

Results

A total of 3,359 nerve reconstruction cases were logged by 1,542 individual candidates from examination years 2004 to 2018. Of the nerve reconstruction codes, 2.1% were nerve transfer codes. There was a statistically significant increase in the proportion of nerve transfer codes over the study period, from 0% of nerve reconstruction codes in examination years 2004 to 2006 to 4.1% of nerve reconstruction codes in examination years 2016 to 2018 (Z = –6.82; P < .001).

Conclusions

There has been an increase in the number of nerve transfer procedures relative to all nerve reconstruction codes for peripheral nerve conditions.

Clinical relevance

There is a modest but significant increase in nerve transfer procedures over time among newly trained orthopedic surgeons, which suggests the need for long-term outcomes studies for nerve transfers procedures performed in the setting of peripheral nerve conditions.

Femoral nerve decompression and sartorius-to-quadriceps nerve transfers for partial femoral nerve injury: a cadaveric study and early case series

OBJECTIVE

Partial femoral nerve injuries cause significant disability with ambulation. Due to their more proximal and superficial location, sartorius branches are often spared in femoral nerve injuries. In this article, the authors report the benefits of femoral nerve decompression, demonstrate the feasibility of sartorius-to-quadriceps nerve transfers in a cadaveric study, describe the surgical technique, and report clinical results.

METHODS

Four fresh-frozen cadaveric lower limbs were dissected for anatomical analysis of the sartorius nerve. In addition, a retrospective review of patients with partial femoral nerve injuries treated with femoral nerve decompression and sartorius-to-quadriceps nerve transfers was conducted. Pre- and postoperative knee extension Medical Research Council (MRC) grades and pain scores (visual analog scale) were collected.

RESULTS

Up to 6 superficial femoral branches innervate the sartorius muscle just distal to the inguinal ligament. Each branch yielded an average of 672 nerve fibers (range 99-1850). Six patients underwent femoral nerve decompression and sartorius-to-quadriceps nerve transfers. Four patients also had concomitant obturator-to-quadriceps nerve transfers. At final follow-up (average 13.4 months), all patients achieved MRC grade 4-/5 or greater knee extension. The average preoperative pain score was 5.2, which decreased to 2.2 postoperatively (p = 0.03).

CONCLUSIONS

Femoral nerve decompression and nerve transfer using sartorius branches are a viable tool for restoring function in partial femoral nerve injuries. Sartorius branches serve as ideal donors in quadriceps nerve transfers because they are expendable, are close to their recipients, and have an adequate supply of nerve fibers.

Supercharge End-to-Side Anterior Interosseous-to-Ulnar Motor Nerve Transfer Restores Intrinsic Function in Cubital Tunnel Syndrome

BACKGROUND

The supercharge end-to-side anterior interosseous nerve-to-ulnar motor nerve transfer offers a viable option to enhance recovery of intrinsic function following ulnar nerve injury. However, in the setting of chronic ulnar nerve compression where the timing of onset of axonal loss is unclear, there is a deficit in the literature on outcomes after supercharge end-to-side anterior interosseous nerve-to-ulnar motor nerve transfer.

METHODS

A retrospective study of patients who underwent supercharge end-to-side anterior interosseous nerve-to-ulnar motor nerve transfer for severe cubital tunnel syndrome over a 5-year period was performed. The primary outcomes were improvement in first dorsal interosseous Medical Research Council grade at final follow-up and time to reinnervation. Change in key pinch strength; grip strength; and Disabilities of the Arm, Shoulder and Hand questionnaire scores were also evaluated using paired t tests and Wilcoxon signed rank tests.

RESULTS

Forty-two patients with severe cubital tunnel syndrome were included in this study. Other than age, there were no significant clinical or diagnostic variables that were predictive of failure. There was no threshold of compound muscle action potential amplitude below which supercharge end-to-side anterior interosseous nerve-to-ulnar motor nerve transfer was unsuccessful.

CONCLUSIONS

This study provides the first cohort of outcomes following supercharge end-to-side anterior interosseous nerve-to-ulnar motor nerve transfer in chronic ulnar compression neuropathy alone and underscores the importance of appropriate patient selection. Prospective cohort studies and randomized controlled trials with standardized outcome measures are required.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, IV.

Reverse End-to-Side Anterior Interosseous Nerve-to-Ulnar Motor Transfer for Severe Ulnar Neuropathy

BACKGROUND

Reverse end-to-side anterior interosseous nerve transfer has been reported to enhance treatment of severe, proximal ulnar neuropathy. The authors report on patients with severe neuropathy treated with ulnar nerve transposition and distal reverse end-to-side anterior interosseous nerve transfer.

METHODS

Thirty patients with severe ulnar neuropathy at the elbow were reviewed. Clinical parameters included preoperative and postoperative Medical Research Council muscle strength, clawing, and degree of wasting. Electrodiagnostic data included compound motor action potential and sensory nerve action potential amplitudes. Summary statistics were used for demographic and clinical data. The t test and Wilcoxon signed rank test were used where appropriate.

RESULTS

Average follow-up was 18.6 months. Preoperatively, 20 patients had Medical Research Council less than or equal to grade 1 in hand intrinsics, small finger sensory nerve action potentials were absent in all patients except for three, and average compound motor action potentials were severely reduced (absent in nearly 40 percent) confirming severity. All groups had a statistically significant increase in strength. More than three-quarters of patients noted partial or complete resolution of clawing and intrinsic muscle wasting. Seventy-three percent of patients regained Medical Research Council greater than or equal to grade 3 and 47 percent achieved Medical Research Council greater than or equal to grade 4. Mean time to observation of nascent units was 8.5 months, and 77 percent of patients demonstrated an augmentation of motor unit numbers with forearm pronation on needle electromyography CONCLUSION:: Proximal subcutaneous ulnar nerve transposition when combined with reverse end-to-side anterior interosseous nerve-to-ulnar nerve transfer demonstrates significant clinical and electrodiagnostic improvement of intrinsic muscle function.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, IV.

Bench-to-Bedside Lessons Learned: Commercialization of an Acellular Nerve Graft

Peripheral nerve injury can result in debilitating outcomes including loss of function and neuropathic pain. Although nerve repair research and therapeutic development are widely studied, translation of these ideas into clinical interventions has not occurred at the same rate. At the turn of this century, approaches to peripheral nerve repair have included microsurgical techniques, hollow conduits, and autologous nerve grafts. These methods provide satisfactory results; however, they possess numerous limitations that can prevent effective surgical treatment. Commercialization of Avance, a processed nerve allograft, sought to address limitations of earlier approaches by providing an off-the-shelf alternative to hollow conduits while maintaining many proregenerative properties of autologous grafts. Since its launch in 2007, Avance has changed the landscape of the nerve repair market and is used to treat tens of thousands of patients. Although Avance has become an important addition to surgeon and patient clinical options, the product's journey from bench to bedside took over 20 years with many research and commercialization challenges. This article reviews the events that have brought a processed nerve allograft from the laboratory bench to the patient bedside. Additionally, this review provides a perspective on lessons and considerations that can assist in translation of future medical products.

Mechanisms and outcomes of the supercharged end-to-side nerve transfer: a review of preclinical and clinical studies

Proximal peripheral nerve injuries often result in poor functional outcomes, chiefly because of the long time period between injury and the reinnervation of distal targets, which leads to muscle and Schwann cell atrophy. The supercharged end-to-side (SETS) nerve transfer is a recent technical innovation that introduces donor axons distally into the side of an injured nerve to rapidly innervate and support end organs while allowing for additional reinnervation after a proximal repair at the injury site. However, the mechanisms by which donor axons grow within the recipient nerve, contribute to muscle function, and impact the regeneration of native recipient axons are poorly understood. This uncertainty has slowed the transfer's clinical adoption. The primary objective of this article is to comprehensively review the mechanisms underpinning axonal regeneration and functional recovery after a SETS nerve transfer. A secondary objective is to report current clinical applications in the upper limb and their functional outcomes. The authors also propose directions for future research with the aim of maximizing the clinical utility of the SETS transfer for peripheral nerve surgeons and their patients.

Comparison Between Supercharged Ulnar Nerve Repair by Anterior Interosseous Nerve Transfer and Isolated Ulnar Nerve Repair in Proximal Ulnar Nerve Injuries

PURPOSE

To compare combined ulnar nerve repair with supercharged end-to-side anterior interosseous nerve to ulnar motor nerve transfer (UR+SETS) with conventional isolated ulnar repair techniques in proximal ulnar nerve transection, with respect to intrinsic muscle power recovery and claw hand deformity correction.

METHODS

We conducted a comparative matched-paired series prospectively on 21 patients with proximal ulnar nerve transection injury. Eleven patients were managed by UR+SETS and 10 by isolated ulnar repair. The outcome was reported at 3, 6, 12, and 18 months using the score of Birch and Raji and Brand's criteria.

RESULTS

A total of 21 patients with acute proximal ulnar nerve transection injury had completed 18 months' follow-up. We observed better results in the UR+SETS group regarding the return of intrinsic function and reduction of deformity with earlier improvement in the score of Birch and Raji and Brand's criteria.

CONCLUSIONS

In the short term, UR+SETS transfer appears to result in better intrinsic muscle reinnervation and clawing deformity correction after proximal ulnar nerve transection injury.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic II.

A rat study of the use of end-to-side peripheral nerve repair as a "babysitting" technique to reduce the deleterious effect of chronic denervation

OBJECTIVE

Functional recovery is disappointing after surgical repair of nerves that are injured far from their target organs and/or after delayed repair. In the former case, a nerve transfer that transects a distal nerve fascicle to innervate denervated targets is one strategy to promote nerve regeneration and functional recovery. An alternate strategy tested in this study is to perform an end-to-side neurorrhaphy to "babysit" (protect) the denervated distal nerve stump at the time of nerve repair and reduce the deleterious effect of chronic denervation on nerve regeneration.

METHODS

In the hindlimbs of Sprague-Dawley rats, the common peroneal (CP) nerve was transected unilaterally and the distal CP nerve stump inserted through a perineurial window into the intact tibial (TIB) nerve, i.e., CP-TIB end-to-side neurorrhaphy. In the first experiment, TIB nerve motoneurons that had regenerated and/or sprouted axons into the CP nerve within 3 months were stimulated to elicit contractions, and thereafter, identified with retrograde dyes for counting. In the second experiment, the intact TIB nerve was transected and cross-sutured to a 3-month chronically denervated distal CP nerve stump that had either been "protected" by ingrown TIB nerves after CP-TIB neurorrhaphy or remained chronically denervated. Thereafter, the number of retrogradely labeled TIB nerve motoneurons that had regenerated their nerves within 3 months were counted and reinnervated tibialis anterior (TA) muscles weighed.

RESULTS

A mean (± SE) of 231 ± 83 TIB nerve motoneurons grew into the end-to-side CP distal nerve stump with corresponding ankle flexion; 32% regenerated their axons and 24% sprouted axons from the intact TIB nerve, eliciting ankle flexor-extensor co-contraction. In the second experiment, after a 3-month period of TIB nerve regeneration, significantly more TIB motoneurons regenerated their axons into "protected" than "unprotected" CP distal nerve stumps within 3 months (mean 332 ± 43.6 vs 235 ± 39.3 motoneurons) with corresponding and significantly higher numbers of regenerated nerve fibers, resulting in significantly better recovery of reinnervated TA muscle weight.

CONCLUSIONS

These experiments in rats demonstrated that delayed nerve repair is more effective when the deleterious effects of chronic denervation of the distal nerve stump are reduced by protecting the nerve stump with ingrowing nerve fibers across an end-to-side insertion of the distal nerve stump into a neighboring intact nerve. Such an end-to-side neurorrhaphy may be invaluable as a means of preventing the atrophy of distal nerve stumps and target organs after chronic denervation, which allows for effective reinnervation of the protected distal nerve stumps and target organs over distance and time.

Masseteric nerve supercharge bypass in primary reconstruction of facial nerve

Facial paralysis is a severe disease and presents a formidable treatment challenge. A wide variety of surgical procedures are available with limited evidence. Major risk factors of suboptimal recovery include the duration of paralysis as well as higher age. In this paper, we demonstrate reconstruction of the facial nerve via an intratemporal end-to-end anastomosis and concomitant transfer of an intact masseteric nerve to the side of facial nerve trunk. The supercharge (reverse end-to-side) transfer resulted in preservation of target muscles and faster recovery. Masseteric supercharge bypass may be an acceptable surgical technique to restore muscle function in potentially higher risk cases.

Effect of Reverse End-to-Side (Supercharging) Neurotization in Long Processed Acellular Nerve Allograft in a Rat Model

PURPOSE

Processed acellular nerve allograft (PNA) has been suggested as a convenient tool for overcoming short and medium nerve defects. Although the clinical implications are unclear, animal data suggest that PNA becomes less effective at longer lengths. Although reverse or supercharging end-to-side nerve transfer may improve the neurotrophic potential in chronically denervated nerve tissue, the application of this strategy to long acellular nerve allograft has not been previously investigated. We hypothesized that supercharging acellular nerve allograft would increase its effective length.

METHODS

Sprague-Dawley and Thy1-green fluorescent protein Sprague-Dawley rats underwent transection of the tibial nerve, followed by immediate repair with 20-, 40-, or 60-mm acellular nerve allografts processed identically to commercially available human acellular nerve allograft (AxoGen, Inc., Alachua, FL) or isograft. Half of the allograft group was supercharged with a reverse end-to-side transfer from the ipsilateral peroneal nerve. At 10 weeks, the reconstructed nerve in the Thy1-green fluorescent rat groups were exposed and examined under a fluorescence-enabled microscope. At 20 weeks, the remaining rats underwent motor testing and tissue harvest for morphological examination.

RESULTS

In comparison with a nonenhanced allograft, supercharging had a statistically significant positive impact on the reinnervated muscle normalized force generation and distal axon counts for all graft sizes. Muscles in the supercharged group were heavier than those in the allograft group for the 40-mm-length grafts and G-ratio measurements were higher in the supercharged allograft group for 60-mm-length grafts only.

CONCLUSIONS

This study supports that hypothesis that supercharging nerve transfer improves axon regeneration within PNA.

CLINICAL RELEVANCE

When an appropriate donor nerve is available, supercharging nerve transfer may improve nerve regeneration in PNA across long nerve defects.

Analysis of human acellular nerve allograft combined with contralateral C7 nerve root transfer for restoration of shoulder abduction and elbow flexion in brachial plexus injury: a mean 4-year follow-up

OBJECTIVE

Human acellular nerve allograft applications have increased in clinical practice, but no studies have quantified their influence on reconstruction outcomes for high-level, greater, and mixed nerves, especially the brachial plexus. The authors investigated the functional outcomes of human acellular nerve allograft reconstruction for nerve gaps in patients with brachial plexus injury (BPI) undergoing contralateral C7 (CC7) nerve root transfer to innervate the upper trunk, and they determined the independent predictors of recovery in shoulder abduction and elbow flexion.

METHODS

Forty-five patients with partial or total BPI were eligible for this retrospective study after CC7 nerve root transfer to the upper trunk using human acellular nerve allografts. Deltoid and biceps muscle strength, degree of shoulder abduction and elbow flexion, Semmes-Weinstein monofilament test, and static two-point discrimination (S2PD) were examined according to the modified British Medical Research Council (mBMRC) scoring system, and disabilities of the arm, shoulder, and hand (DASH) were scored to establish the function of the affected upper limb. Meaningful recovery was defined as grades of M3-M5 or S3-S4 based on the scoring system. Subgroup analysis and univariate and multivariate logistic regression analyses were conducted to identify predictors of human acellular nerve allograft reconstruction.

RESULTS

The mean follow-up duration and the mean human acellular nerve allograft length were 48.1 ± 10.1 months and 30.9 ± 5.9 mm, respectively. Deltoid and biceps muscle strength was grade M4 or M3 in 71.1% and 60.0% of patients. Patients in the following groups achieved a higher rate of meaningful recovery in deltoid and biceps strength, as well as lower DASH scores (p < 0.01): age < 20 years and age 20-29 years; allograft lengths ≤ 30 mm; and patients in whom the interval between injury and surgery was < 90 days. The meaningful sensory recovery rate was approximately 70% in the Semmes-Weinstein monofilament test and S2PD. According to univariate and multivariate logistic regression analyses, age, interval between injury and surgery, and allograft length significantly influenced functional outcomes.

CONCLUSIONS

Human acellular nerve allografts offered safe reconstruction for 20- to 50-mm nerve gaps in procedures for CC7 nerve root transfer to repair the upper trunk after BPI. The group in which allograft lengths were ≤ 30 mm achieved better functional outcome than others, and the recommended length of allograft in this procedure was less than 30 mm. Age, interval between injury and surgery, and allograft length were independent predictors of functional outcomes after human acellular nerve allograft reconstruction.

Protective distal side-to-side neurorrhaphy in proximal nerve injury-an experimental study with rats

Background

Side-to-side neurorrhaphy may protect the denervated end organ and preserve the initial connection with proximal stump. We examined the effect of protective side-to-side anastomosis on nerve and end organ regeneration in proximal nerve injury model.

Methods

The left common peroneal nerve of 24 Sprague Dawley rats was proximally transected. In groups B and C, side-to-side neurorrhaphy was performed distally between the peroneal and tibial nerves without (group B) and with (group C) partial donor nerve axotomy inside the epineural window. Group A served as an unprotected control. After 26 weeks, the proximal transection was repaired with end-to-end neurorrhaphy on all animals. Regeneration was followed during 12 weeks with the walk track analysis. Morphometric studies and wet muscle mass calculations were conducted at the end of the follow-up period.

Results

The results of the walk track analysis were significantly better in groups B and C compared to group A. Groups B and C showed significantly higher wet mass ratios of the tibialis anterior and extensor digitorum longus muscle compared to group A. Group C showed significantly higher morphometric values compared to group A. Group B reached higher values of the fibre count, fibre density, and percentage of the fibre area compared to group A.

Conclusions

Protective distal side-to-side neurorrhaphy reduced muscle atrophy and had an improving effect on the morphometric studies and walk track analysis. Distal side-to-side neurorrhaphy does not prevent the regenerating axons to grow from the proximal stump to achieve distal nerve stump.

Novel Uses of Nerve Transfers

Nerve transfer surgery involves using a working, functional nerve with an expendable or duplicated function as a donor to supply axons and restore function to an injured recipient nerve. Nerve transfers were originally popularized for the restoration of motor function in patients with peripheral nerve injuries. However, more recently, novel uses of nerve transfers have been described, including nerve transfers for sensory reinnervation, nerve transfers for spinal cord injury and stroke patients, supercharge end-to-side nerve transfers, and targeted muscle reinnervation for the prevention and treatment of postamputation neuroma pain. The uses for nerve transfers and the patient populations that can benefit from nerve transfer surgery continue to expand. Awareness about these novel uses of nerve transfers among the medical community is important in order to facilitate evaluation and treatment of these patients by peripheral nerve specialists. A lack of knowledge of these techniques continues to be a major barrier to more widespread implementation.

Testing the effectiveness and the contribution of experimental supercharge (reversed) end-to-side nerve transfer

OBJECTIVE

Supercharge end-to-side (SETS) transfer, also referred to as reverse end-to-side transfer, distal to severe nerve compression neuropathy or in-continuity nerve injury is gaining clinical popularity despite questions about its effectiveness. Here, the authors examined SETS distal to experimental neuroma in-continuity (NIC) injuries for efficacy in enhancing neuronal regeneration and functional outcome, and, for the first time, they definitively evaluated the degree of contribution of the native and donor motor neuron pools.

METHODS

This study was conducted in 2 phases. In phase I, rats (n = 35) were assigned to one of 5 groups for unilateral sciatic nerve surgeries: group 1, tibial NIC with distal peroneal-tibial SETS; group 2, tibial NIC without SETS; group 3, intact tibial and severed peroneal nerves; group 4, tibial transection with SETS; and group 5, severed tibial and peroneal nerves. Recovery was evaluated biweekly using electrophysiology and locomotion tasks. At the phase I end point, after retrograde labeling, the spinal cords were analyzed to assess the degree of neuronal regeneration. In phase II, 20 new animals underwent primary retrograde labeling of the tibial nerve, following which they were assigned to one of the following 3 groups: group 1, group 2, and group 4. Then, secondary retrograde labeling from the tibial nerve was performed at the study end point to quantify the native versus donor regenerated neuronal pool.

RESULTS

In phase I studies, a significantly increased neuronal regeneration in group 1 (SETS) compared with all other groups was observed, but with modest (nonsignificant) improvement in electrophysiological and behavioral outcomes. In phase II experiments, the authors discovered that secondary labeling in group 1 was predominantly contributed from the donor (peroneal) pool. Double-labeling counts were dramatically higher in group 2 than in group 1, suggestive of hampered regeneration from the native tibial motor neuron pool across the NIC segment in the presence of SETS.

CONCLUSIONS

SETS is indeed an effective strategy to enhance axonal regeneration, which is mainly contributed by the donor neuronal pool. Moreover, the presence of a distal SETS coaptation appears to negatively influence neuronal regeneration across the NIC segment. The clinical significance is that SETS should only employ synergistic donors, as the use of antagonistic donors can downgrade recovery.