Direct Neurotization: Past, Present, and Future Considerations

ABSTRACT

Direct neurotization is a method that involves direct implantation of nerve fascicles into a target tissue, that is, muscle fibers, skin, cornea, and so on, with the goal of restoring aesthetic, sensation and or functional capacity. This technique has been implemented since the early 1900s, with numerous experimental and clinical reports of success. Applications have included both sensory and motor neurotization of muscle, as well as protective sensory provision for other organs. These techniques have been used to restore corneal sensation, repair brachial plexus injuries, reestablish tongue movement and function through direct tongue neurotization, and reinnervate multiple facial muscles in patients with facial paralysis. Most recently, these methods have even been used in conjunction with acellular cadaveric nerve grafts to directly neurotize skin. Indications for direct neurotization remain limited, including those in which neural coaptation is not feasible (ie, surgical or traumatic damage to neuromuscular junction, severe avulsion injuries of the distal nerve); however, the success and wide-range application of direct neurotization shows its potential to be implemented as an adjunct treatment in contrast to views that it should solely be used as a salvage therapy. The purpose of the following review is to detail the historic and current applications of direct neurotization and describe the future areas of investigation and development of this technique.

[Modification of intercostobrachial neurotization of musculocutaneous and axillary nerves in total brachial plexopathy: description of technique and literature review]

BACKGROUND

Intercostobrachial neurotization is one of the few approach for partial motor recovery of extremity in patients with total trauma of brachial plexus. However, direct coaptation with musculocutaneous nerve is often impossible due to different anatomy of intercostal nerves and their functional failure at several levels. This necessitates the use of intermediate graft that deteriorates the final outcome.

OBJECTIVE

To develop an alternative method for direct coaptation of musculocutaneous nerve with insufficiently long intercostal donor nerves.

MATERIAL AND METHODS

The study included 26 patients with total post-traumatic plexitis. All patients underwent intercostobrachial neurotization of musculocutaneous and axillary nerves. Original technique of direct selective neurotization of motor fascicular groups of musculocutaneous and axillary nerves was used in 11 cases.

RESULTS AND DISCUSSION

A modified variant of intercostobrachial neurotization of musculocutaneous and axillary nerves consists in mobilization and transposition of recipient nerves in axillary region. This makes it possible to reduce the distance to donor nerves and, in most cases, to carry out direct neurotization without autologous grafts. Among 11 patients, restoration of shoulder abduction and elbow flexion was obtained in 7 patients (77 %).

CONCLUSION

The proposed adaptive technique makes it possible to avoid graft lengthening in some cases and provides satisfactory results.

Nerve recovery from treatment with a vascularized nerve graft compared to an autologous non-vascularized nerve graft in animal models: A systematic review and meta-analysis

Background

Treatment of nerve injuries proves to be a worldwide clinical challenge. Vascularized nerve grafts are suggested to be a promising alternative for bridging a nerve gap to the current gold standard, an autologous non-vascularized nerve graft. However, there is no adequate clinical evidence for the beneficial effect of vascularized nerve grafts and they are still disputed in clinical practice.

Objective

To systematically review whether vascularized nerve grafts give a superior nerve recovery compared to non-vascularized nerve autografts regarding histological and electrophysiological outcomes in animal models.

Material and methods

PubMed and Embase were systematically searched. The inclusion criteria were as follows: 1) the study was an original full paper which presented unique data; 2) a clear comparison between a vascularized and a non-vascularized autologous nerve transfer was made; 3) the population study were animals of all genders and ages. A standardized mean difference and 95% confidence intervals for each comparison was calculated to estimate the overall effect. Subgroup analyses were conducted on graft length, species and time frames.

Results

Fourteen articles were included in this review and all were included in the meta-analyses. A vascularized nerve graft resulted in a significantly larger diameter, higher nerve conduction velocity and axonal count compared to an autologous non-vascularized nerve graft. However, during sensitivity analysis the effect on axonal count disappeared. No significant difference was observed in muscle weight.

Conclusion

Treating a nerve gap with a vascularized graft results in superior nerve recovery compared to non-vascularized nerve autografts in terms of axon count, diameter and nerve conduction velocity. No difference in muscle weight was seen. However, this conclusion needs to be taken with some caution due to the inherent limitations of this meta-analysis. We recommend future studies to be performed under conditions more closely resembling human circumstances and to use long nerve defects.

Reliability of deep branch of ulnar nerve identification in interosseous-to-ulnar motor nerve transfer: A cadaver study of 20 wrists

Reinnervation of the intrinsic hand muscles after proximal ulnar nerve repair is often unsatisfactory. Promising results have nevertheless been reported recently for supercharged end-to-side anterior interosseous to deep branch of the ulnar nerve (DBUN) transfer. The aim of this study was to determine whether the DBUN can be reliably identified without retrograde intraneural dissection from Guyon's canal. Twenty cadaveric wrists were dissected. In a first stage, nerve transfer was performed through a limited 4 cm incision without releasing Guyon's canal. In a second stage, correct identification of the DBUN was assessed by retrograde intraneural dissection from its point of exit from Guyon's canal. The DBUN was correctly identified in 18 of the 20 wrists (90%). Although anatomical landmarks provide valuable clues, identifying the DBUN by neurolysis is technically challenging. All the elements required for nerve transfer can be exposed through a 4 cm incision, but the DBUN was nevertheless incorrectly identified in 10% of cases. Guyon canal release seems advisable to guarantee correct DBUN identification.

A consecutive series of targeted muscle reinnervation (TMR) cases for relief of neuroma and phantom limb pain: UK perspective

BACKGROUND

Studies have suggested that targeted muscle reinnervation (TMR) can improve symptoms of neuroma pain (NP) and phantom limb pain (PLP) in patients.

OBJECTIVES

Our primary objective was to measure changes in NP and PLP levels following TMR surgery at 4-time points (baseline, 3, 6- and 12-months postoperatively). Secondary aims included identification of the character and rate of any surgical complications and patients' satisfaction with TMR.

METHODS

A retrospective review of outcomes of 36 patients who underwent TMR surgery to treat intractable NP and/or PLP after major amputation of an upper (UL) or lower limb (LL) at a single centre in London, UK over 7 years. The surgical techniques, complications, and satisfaction with TMR are described.

RESULTS

Forty TMR procedures were performed on 36 patients. Thirty patients had complete data for NP and PLP levels at all pre-defined time points. Significant improvements (p<0.01) in both types of pain were observed for both upper and LL amputees. However, there were varying patterns of recovery. For example, UL amputees experienced worsening of PLP in the first few months post-operatively whereas surgical complications were more common in LL cases. Patients were overwhelmingly satisfied with the improvements in their symptoms (90%).

CONCLUSIONS

TMR surgery appeared to relieve both NP and PLP although the retrospective nature of this study limits the strength of this conclusion. However, complication rates were high, and it is crucial for surgeons and patients to fully understand the course and outcomes of this novel surgery prior to undertaking treatment.

A supportive donor nerve for long-term facial paralysis: Anatomical analysis of the posterior auricular nerve and micro-anatomical comparison with zygomatic nerve

BACKGROUND

The posterior auricular nerve (PAN) is an inspiring candidate for the additional axonal source in long-term facial paralysis to improve the functional results of the cross-facial nerve (FN) graft technique. However, no studies have analyzed the PAN's axonal load and its microscopic anatomy to assess its utilization in facial reanimation. The present study aims to examine the anatomical and microscopic features of the PAN to analyze its feasibility as a donor nerve.

METHODS

The bilateral facial side of 14 fresh frozen adult human cadavers was examined for the study. The PAN's anatomical course was recorded, and nerve specimens from the PAN and zygomatic nerve (ZN) were obtained to compare their microscopic anatomy and axon counts using a light microscope and transmission electron microscope.

RESULTS

The PAN's average branching distance and its course length were 5.8 ± 2.69 mm and 59.2 ± 5.85, respectively. The mean number of myelinated axons was 600.28 ± 69.97 in the PAN and 728.85 ± 166.31 in the ZN. This difference between the two nerves was statistically significant (p = 0.002). However, considering the gender variable, the mean axon counts of PAN and ZN were statistically similar for face sides and their average. Furthermore, the ultrastructural anatomy of both nerves was similar in electron microscopic evaluation.

CONCLUSIONS

The present study confirms that the PAN is a proper candidate to be a supportive donor nerve due to its isolated site, consistent anatomical course, convenient ultrastructural anatomy as well as axonal load.

Functional Outcomes of Nerve Allografts Seeded with Undifferentiated and Differentiated Mesenchymal Stem Cells in a Rat Sciatic Nerve Defect Model

BACKGROUND

Mesenchymal stem cells have the potential to produce neurotrophic growth factors and establish a supportive microenvironment for neural regeneration. The purpose of this study was to determine the effect of undifferentiated and differentiated mesenchymal stem cells dynamically seeded onto decellularized nerve allografts on functional outcomes when used in peripheral nerve repair.

METHODS

In 80 Lewis rats, a 10-mm sciatic nerve defect was reconstructed with (1) autograft, (2) decellularized allograft, (3) decellularized allograft seeded with undifferentiated mesenchymal stem cells, or (4) decellularized allograft seeded with mesenchymal stem cells differentiated into Schwann cell-like cells. Nerve regeneration was evaluated over time by cross-sectional tibial muscle ultrasound measurements, and at 12 and 16 weeks by isometric tetanic force measurements, compound muscle action potentials, muscle mass, histology, and immunofluorescence analyses.

RESULTS

At 12 weeks, undifferentiated mesenchymal stem cells significantly improved isometric tetanic force measurement and compound muscle action potential outcomes compared to decellularized allograft alone, whereas differentiated mesenchymal stem cells significantly improved compound muscle action potential outcomes. The autografts outperformed both stem cell groups histologically at 12 weeks. At 16 weeks, functional outcomes normalized between groups. At both time points, the effect of undifferentiated versus differentiated mesenchymal stem cells was not significantly different.

CONCLUSIONS

Undifferentiated and differentiated mesenchymal stem cells significantly improved functional outcomes of decellularized allografts at 12 weeks and were similar to autograft results in the majority of measurements. At 16 weeks, outcomes normalized as expected. Although differences between both cell types were not statistically significant, undifferentiated mesenchymal stem cells improved functional outcomes of decellularized nerve allografts to a greater extent and had practical benefits for clinical translation by limiting preparation time and costs.

Transfer of Motor Fascicle From the Median to the Axillary Nerve for Upper Brachial Plexus Injury: A Surgical Technique and Case Report

Upper brachial plexus injury or isolated lesions of the axillary nerve (AN) compromise shoulder functionality significantly. Different surgical techniques have been described for selective reconstruction of the AN, with good results especially in association with repair of the suprascapular nerve. The objective of this study is to describe the transfer of motor fascicles of the median nerve to the AN by an axillary approach in cadavers and the clinical results in 2 patients. Dissections were performed on 5 cadavers, followed by identification and dissection of the AN and its divisions before entering the quadrangular space. We standardized the surgical technique in which the median nerve was first identified and then an intrafascicular dissection was performed. Then we harvested a fascicle and transferred it to the anterolateral branch of the AN. Two patients underwent an operation; at 2 years of follow-up, average abduction of 125 degrees and external rotation of 95 degrees were observed. In conclusion, the transfer of motor fascicles of the median nerve to the AN by an axillary approach could be an alternative technique for the deltoid reinnervation in upper brachial plexus injury. Some advantages are the proximity of the donor nerve to the receptor nerve and the low morbidity of the target muscles of the donor nerve. Studies with a larger number of patients are required to establish its effectiveness compared with other techniques already described.

Contralateral C7 nerve transfer through posterior vertebral approach combined with selective posterior rhizotomy of the affected cervical nerve in the treatment of central upper limb spastic paralysis: A case report

INTRODUCTION

C7 nerve transfer alone can improve upper limb motor function and partial spasticity. Selective posterior rhizotomy (SPR) of the cervical nerve alone can comprehensively improve spasticity but without neuromotor regeneration. We propose a novel possible improvement of contralateral C7 (CC7) nerve transfer through the posterior vertebral approach, which was combined with SPR of the affected cervical nerve.

PATIENT CONCERNS

A 33-year-old male patient presented with cerebral hemorrhage of the left basal ganglia, paralysis of the right limbs, and hypesthesia 8 months earlier. The dysfunction of the affected hand was already present at admission. The patient reported a previous history of hypertension for several years and oral antihypertensive drugs, and blood pressure was controlled within a normal range.

DIAGNOSIS

Central upper limb spastic paralysis. The muscle strength of the right lower limb was grade IV. The Fugl-Meyer score of the right upper limb was 7 points, and the modified Ashworth score was 10.

INTERVENTIONS

The patient underwent CC7 transfer and SPR.

OUTCOMES

The patient successfully underwent CC7 transfer and SPR without complications. On the day after surgery, the left upper limb motions were normal. The Fugl-Meyer score was 9, and the modified Ashworth score of the right upper limb was 2.

CONCLUSIONS

CC7 nerve transfer through the posterior vertebral approach combined with SPR of the affected cervical nerve can possibly improve the surgical outcomes of selected patients with upper limb motor dysfunction and partial spasticity. This method has not been reported in the literature before, and additional studies are necessary.

Saphenous nerve to posterior tibial nerve transfer: A new approach to restore sensations of sole in diabetic sensory polyneuropathy

BACKGROUND

Loss of sensations in the sole following diabetic sensorimotor polyneuropathy (DSPN) leads to diabetic foot ulcers and its sequelae. We hypothesized that sensory reinnervation of sole by transfer of saphenous nerve (SN) to sensory fascicles of posterior tibial nerve (PTN) in these patients may reverse the neuropathy.

METHODS

This prospective interventional case series included patients with advanced DSPN and intact sensory supply of SN. PTN was neurotized by transfer of SN nerve in the tarsal tunnel and postoperatively sensations of the sole were tested. Any existing ulcers on sole were noted and their healing was monitored.

FINDING

A total of 17 patients (22 feet), 9 male and 8 female, were included. Seven patients had ulcers in the feet. At 6 months follow-up all patients developed protective sensation in the sole. The average 2 PD improved from 60 mm to 45.5 mm, average vibration perception improved from 34.12 V to 24.33, Medical Research Council (MRC) score improved from S0 in 12 feet and S1 in 10 feet to S3+ in 13 feet, S3 in 5 feet, and S2 in 2 feet at 6 months along with healing of ulcers in all 7 feet.

INTERPRETATION

Transfer of SN to PTN for sensory neurotization is an innovative and simple option to prevent complications of DSPN. This procedure has the potential to change the natural history of DSPN.

[Nerve transfer in patients with tetraplegia: improvement in hand function]

Reconstruction of arm and hand function in patients with a cervical spinal cord injury can improve their quality of life. Elbow extension, wrist extension, grip function and opening of the hand can be reconstructed. Traditionally, this has been done through tendon transpositions. Nerve transfer is a new technique. A functioning motor nerve branch is moved and connected to a muscle or muscle group damaged by the spinal cord injury. This technique has several advantages. Multiple functions can be restored by one nerve transfer, no long-term hand-rehabilitation is required and there is no risk of adhesions of the transposition. The most important disadvantage is the recovery time, as a results of the slow ingrowth of the nerve transfer, which takes at least 12 to 18 months. For each spinal cord injury patient, an individual action plan must be made, because not every patient has the same options and these are sometimes very limited.

Erectile Functional Restoration With Genital Branch of Genitofemoral Nerve to Pelvic Nerve Transfer After Spinal Root Transection in Rats

OBJECTIVE

To investigate the feasibility of erectile function restoration by the genitofemoral nerve to pelvic nerve transfer in rats.

METHODS

Thirty-six male rats were included in this study. Rats in the nerve transfer group (n = 12) were subjected to pelvic nerve, sacral roots, and L6 roots transection and then bilateral genitofemoral nerve to pelvic nerve transfer, rats in the nerve resection group (n = 12) were subjected to pelvic nerve, sacral roots, and L6 roots transection without nerve transfer, and rats in the control group (n = 12) served as controls. After reinnervation, intracavernous pressure (ICP) assessment was performed. Fluoro-Gold was injected into the corpus cavernosum. Immediately before euthanasia, transferred nerves were stimulated to test penile intracavernous pressure. The L6, S1, and L1-2 spinal cord segments were used for retrogradely labeled neurons. Regenerative nerve morphologic examination assessment was performed.

RESULTS

Genitofemoral nerve stimulation induced an increase in ICP in the nerve transfer group. The mean ICP in this group was (33.8 ± 9.4 mm Hg), which is higher than the mean value in the nerve resection group (3.9 ± 1.0 mm Hg) but lower than that in the control group (69.8 ± 12.2 mm Hg; P < .05). The formation of new neural pathways was confirmed by the appearance of Fluoro-Gold labeled neurons in the L-1 and L-2 spinal cord segments in the nerve transfer group. Regenerative nerve morphologic examination showed good axonal regeneration after genitofemoral nerve transfer.

CONCLUSION

Nerve regeneration can be obtained by genitofemoral nerve to pelvic nerve transfer, and erectile function can be restored.

Differences in strength fatigue when using different donors in traumatic brachial plexus injuries

BACKGROUND

The purpose of this study was to assess the results of elbow flexion strength fatigue, rather than the maximal power of strength, after brachial plexus re-innervation with phrenic and spinal accessory nerves. We designed a simple but specific test to study whether statistical differences were observed among those two donor nerves.

METHOD

We retrospectively reviewed patients with severe brachial plexus palsy for which either phrenic nerve (PN) or spinal accessory nerve (SAN) to musculocutaneous nerve (MCN) transfer was performed. A dynamometer was used to determine the maximal contraction strength. One and two kilograms circular weights were utilized to measure isometrically the duration of submaximal and near-maximal contraction time. Statistical analysis was performed between the two groups.

RESULTS

Twenty-eight patients were included: 21 with a PN transfer while 7 with a SAN transfer for elbow flexion. The mean time from trauma to surgery was 7.1 months for spinal accessory nerve versus 5.2 for phrenic nerve, and the mean follow-up was 57.7 and 38.6 months, respectively. Statistical analysis showed a quicker fatigue for the PN, such that patients with the SAN transfer could hold weights of 1 kg and 2 kg for a mean of 91.0 and 61.6 s, respectively, while patients with transfer of the phrenic nerve could hold 1 kg and 2 kg weights for just a mean of 41.7 and 19.6 s, respectively. Both differences were statistically significant (at p = 0.006 and 0.011, respectively). Upon correlation analysis, endurances at 1 kg and 2 kg were strongly correlated, with r = 0.85 (p < 0.001).

CONCLUSIONS

Our results suggest that phrenic to musculocutaneous nerve transfer showed an increased muscular fatigue when compared with spinal accessory nerve to musculocutaneous transfer. Further studies designed to analyze this relation should be performed to increase our knowledge about strength endurance/fatigue and muscle re-innervation.

Reanimation of triceps muscle using ulnar nerve fascicle transfer to the nerve to long head of the triceps muscle

BACKGROUND

Triceps muscle serves an important role in extension of the elbow. Its action is required for reaching out objects without using the trunk. Elbow extension is an important function for natural stabilization of the elbow. The aim of this study was to evaluate restoration of elbow extension in adults suffering triceps muscle palsy with various causes, by using transfer of a fascicle of ulnar nerve to the long head of triceps branch of the radial nerve.

MATERIALS AND METHODS

In the present case series, 7 patients with partial brachial plexus injury or posterior cord injury, where triceps muscle was involved, were subjected to motor fascicle of ulnar nerve transfer to the nerve to long head of triceps for restoration of elbow extension. Follow-ups, including EMG-NCV (electromyography-nerve conduction velocity) 6 and 12 months after surgery and elbow extension muscle strength using MRC grading, were carried out.

RESULTS

Six patients (85.71%) achieved a functional muscle strength of M4 for their elbow extension. In all of the patients, re-innervation was discovered using EMG-NCV.

CONCLUSION

This surgical technique (ulnar nerve fascicle transfer to long head of the triceps) for improving elbow extension is promising in patients with brachial plexus injury.

Intercostal nerve transfer for restoration of the diaphragm muscle function after phrenic nerve transfer in total brachial plexus avulsion

OBJECT

To determine the possibility of innervation of the diaphragm muscle using intercostal nerve after ipsilateral phrenic nerve transfer in total brachial plexus avulsion.

METHODS

Bilateral phrenic nerves and the 9th intercostal nerves were observed inside the thorax. The point where the phrenic nerve entered the diaphragm muscle (point A), the point where the 9th intercostal nerve gave rise to the cutaneous branch (point B) and crossed the posterior axillary line (point C) and the point where the posterior axillary line met the insertion of the diaphragm muscle (point D) were identified. The distances between points B and C, points A and C and from points A through D to C were recorded respectively. The 9th intercostal nerve was transferred to the distal stump of the phrenic nerve in one patient after phrenic nerve transfer to avulsed brachial plexus.

RESULTS

The mean distances between points B and C, points A and C and from points A through D to C were 12.20 ± 1.04 cm, 10.32 ± 1.02 cm and 16.43 ± 0.91 cm on the right side respectively, 11.78 ± 1.21 cm, 7.77 ± 0.85 cm and 11.74 ± 1.00 cm on the left side respectively. The 9th intercostal nerve was used to innervate the distal stump of the phrenic nerve in one patient after the phrenic nerve transfer to the avulsed brachial plexus. The diaphragm muscle function partially recovered one year after the operation.

CONCLUSION

The 9th intercostal nerve can be transferred to the distal stump of the phrenic nerve to restore the diaphragm muscle function according to the anatomical study. The movement of the diaphragm muscle was partially restored in one clinical case.

Evaluation of Intrinsic Hand Musculature Reinnervation following Supercharge End-to-Side Anterior Interosseous-to-Ulnar Motor Nerve Transfer

Supercharge end-to-side anterior interosseous-to-ulnar motor nerve transfer is commonly performed in the authors' institution to augment intrinsic hand function. Following observations of recovery patterns, the authors hypothesized that despite its more distal innervation, the first dorsal interosseous muscle recovers to a greater extent than the abductor digiti minimi muscle. The objective of this work was to evaluate the clinical and electrodiagnostic pattern of reinnervation of intrinsic hand musculature following supercharge end-to-side anterior interosseous-to-ulnar motor nerve transfer. A retrospective cohort of prospectively collected data included all patients who underwent a supercharge end-to-side anterior interosseous-to-ulnar motor nerve transfer. Two independent reviewers performed data collection. Reinnervation was assessed with two primary outcome measures: (1) clinically, with serial Medical Research Council strength assessments; and (2) electrodiagnostically, with serial motor amplitude measurements. Statistical analysis was performed using nonparametric statistics. Seventeen patients (65 percent male; mean age, 56.9 ± 13.3 years) were included with a mean follow-up of 16.7 ± 8.5 months. Preoperatively, all patients demonstrated clinically significant weakness and electrodiagnostic evidence of denervation. Postoperatively, strength and motor amplitude increased significantly for both the first dorsal interosseous muscle (p = 0.002 and p = 0.016) and the abductor digiti minimi muscle (p = 0.044 and p = 0.015). Despite comparable preoperative strength (p = 0.098), postoperatively, the first dorsal interosseous muscle achieved significantly greater strength when compared to the abductor digiti minimi muscle (p = 0.023). Following supercharge end-to-side anterior interosseous-to-ulnar motor nerve transfer, recovery of intrinsic muscle function differs between the abductor digiti minimi and the first dorsal interosseous muscles, with better recovery observed in the more distally innervated first dorsal interosseous muscle. Further work to elucidate the underlying physiologic and anatomical basis for this discrepancy is indicated. CLINICAL QUESTION/LEVEL OF EVIDENCE:: Therapeutic, IV.

Powering the Gracilis for Facial Reanimation: A Systematic Review and Meta-analysis of Outcomes Based on Donor Nerve

Importance

Free gracilis transfer for dynamic reanimation in chronic facial paralysis is the gold standard, but there remains a need to better understand outcomes with respect to the donor nerve.

Objective

To characterize outcomes in adults undergoing primary gracilis transfer for facial paralysis stratified by donor nerve used for neurotization.

Data Sources

Search strategies were used in Ovid MEDLINE (1946-2019), Embase (1947-2019), Scopus (1823-2019), Cochrane Central Register of Controlled Trials (CENTRAL), and ClinicalTrials.gov (1997-2019).

Study Selection

Inclusion and exclusion criteria were designed to capture studies in adults with unilateral chronic facial paralysis undergoing single-paddle free gracilis transfer. All study types were included except case reports. Abstracts and full texts were reviewed in duplicate. Of 130 unique citations, 10 studies including 295 patients were included after applying inclusion and exclusion criteria. Data were analyzed between November 2018 and December 2019.

Data Extraction and Synthesis

PRISMA guidelines were followed. The Newcastle-Ottawa scale was used to assess study quality, and the Cochrane Risk of Bias tool was used to assess risk of bias. Independent extraction by 2 authors (P.M.V. and J.J.C.) was performed. Data were pooled using a random-effects model.

Main Outcomes and Measures

Owing to heterogeneity in reporting of facial reanimation outcomes, we first performed a systematic review, and then compiled available outcomes for meta-analysis. Outcomes studied for meta-analysis were oral commissure excursion and facial symmetry.

Results

Meta-analysis of masseteric nerve (MN) (n = 56) vs cross-facial nerve graft (CFNG) (n = 52) in 3 retrospective studies showed no statistical heterogeneity between these studies (I2 = 0%), and the standardized mean difference (SMD) was greater for MN (0.55; 95% CI, 0.17 to 0.94). Meta-analysis of angles of symmetry in 2 retrospective studies comparing MN (n = 51) to CFNG (n = 47) both at rest (-0.22; 95% CI, -0.63 to 0.18) and with smiling (-0.14; 95% CI, -0.73 to 0.46) were better with MN, though the difference was not statistically significant.

Conclusions and Relevance

Owing to heterogeneity in reported outcomes from facial reanimation, we were unable to make definitive conclusions regarding the optimal donor nerve. Establishing a reporting standard at peer-reviewed journals to improve results reporting is one method to allow for improved collaboration in the future. Standardizing follow-up times, assessing spontaneity in an objective and reproducible fashion, and use of consistent outcome measures would allow for future meta-analyses and better understanding of options for facial reanimation.

Lower subscapular nerve transfer for axillary nerve repair in upper brachial plexus palsy

BACKGROUND

The potential to utilize the lower subscapular nerve for brachial plexus surgery has been suggested in many anatomical studies. However, we know of no studies in the literature describing the use of the lower subscapular nerve for axillary nerve reconstruction to date. This study aimed to examine the effectiveness of this nerve transfer in patients with upper brachial plexus palsy.

METHODS

Of 1340 nerve reconstructions in 568 patients with brachial plexus injury performed by the senior author (P.H.), a subset of 18 patients underwent axillary nerve reconstruction using the lower subscapular nerve and constitutes the patient group for this study. The median age was 48 years, and the median time between trauma and surgery was 6 months. A concomitant radial nerve injury was found in 8 patients.

RESULTS

Thirteen patients completed a minimum follow-up period of 24 months. Successful deltoid recovery was defined as (1) muscle strength MRC grade ≥ 3, (2) electromyographic signs of reinnervation, and (3) increase in deltoid muscle mass. Axillary nerve reconstruction was successful in 9 of 13 patients, which represents a success rate of 69.2%. No significant postoperative weakness of shoulder internal rotation or adduction was observed after transecting the lower subscapular nerve.

CONCLUSIONS

The lower subscapular nerve can be used as a safe and effective neurotization tool for upper brachial plexus injury, having a success rate of 69.2% for axillary nerve repair. Our technique presents a suitable alternative for patients with concomitant radial nerve injury.

Contralateral cervical seventh nerve transfer for spastic arm paralysis via a modified prespinal route: a cadaveric study

BACKGROUND

We proposed contralateral cervical seventh nerve transfer for spastic arm paralysis after central neurological injury in the New England Journal of Medicine (NEJM) in 2018. In this surgery, we applied a new surgical route for nerve transfer, the Huashan prespinal route. The objective of this study was to elaborate our new surgical technique, clarify its relationship to the vertebral artery, and provide anatomical data on this novel method.

METHODS

The effectiveness and safety of the Huashan prespinal route in contralateral C7 nerve transfer were evaluated anatomically. Nine cadavers (4 males, 5 females) were available for this study. Among these, anatomical parameters of the vertebral artery were obtained from 6 cadavers, and the anastomosis of the bilateral cervical seventh nerve was observed on 3 cadavers undergoing contralateral C7 nerve transfer via the Huashan prespinal route.

RESULTS

Tension-free anastomosis of the bilateral cervical seventh nerve was achieved through the Huashan prespinal route. The tilt angle of the vertebral artery to the sagittal plane (with thyroid cartilage as the origin) was 25.5 ± 4.5°, at 22.5 ± 1.6° and 28.7 ± 4.3° on the left and right side, respectively. The safe drilling angle to penetrate through the longus colli muscles for the creation of a longus colli muscle tunnel to avoid injury to the vertebral artery in our surgical technique was above 33.2°.

CONCLUSIONS

The cadaveric study confirms that the presented technique allowed simple, effective, and safe contralateral C7 nerve transfer. This technique can be used in the treatment of hemiplegia and brachial plexus injury. There is a safe scope of drilling angle for creating the longus colli muscle tunnel required for this surgical route. The anatomical parameters obtained in this study will be helpful for the performance of this operation.

Upper Extremity Axon Counts and Clinical Implications for Motor Nerve Transfer

BACKGROUND

Nerve transfers are planned based on the following parameters: location, number of branches, and axon count matching of the donor and recipient nerves. The authors have previously defined the former two in upper limb muscles. In the literature, axon counts are obtained from various sources, using different methods of histomorphometry. This study describes the axon counts of the same primary motor nerve branches from the authors' previous study using a uniform method of manual histomorphometry and completes the authors' blueprint of upper limb neuromuscular anatomy for reconstructive surgery.

METHODS

The distal ends of the primary nerve branches of 23 upper limb muscles were harvested from 10 fresh frozen cadaveric upper limbs. Manual quantitative histomorphometry was performed by two independent investigators, and the average was reported.

RESULTS

The primary nerve branches of the arm muscles had higher average axon counts (range, 882 to 1835) compared with those of the forearm muscles (range, 267 to 883). In the forearm, wrist flexor (range, 659 to 746) and extensor (range, 543 to 745) nerve branches had axons counts that were similar to those of potential donors (e.g., supinator, n = 602; pronator teres, n = 625; flexor digitorum superficialis, n = 883; and flexor digitorum profundus, n = 832).

CONCLUSIONS

Apart from describing the axon counts of the upper limb, the authors have found that the forearm axon counts are very comparable. This insight, when combined with information on the location and number of primary nerve branches, will empower surgeons to tailor bespoke nerve transfers for every clinical situation.

Outcomes, Challenges, and Pitfalls after Targeted Muscle Reinnervation in High-Level Amputees: Is It Worth the Effort?

BACKGROUND

Although the distal targets have been lost in proximal upper limb amputees, the neural signals for intuitive hand and arm function are still available and thus can be incorporated into more useful prosthetic function using targeted muscle reinnervation technique. In this article, the authors present their outcomes and range of indications in addition to experiences and pitfalls after 30 targeted muscle reinnervation cases at above-elbow and shoulder disarticulation level of amputation.

METHODS

Thirty patients with above-elbow or shoulder disarticulation amputations were enrolled between 2012 and 2017. Indications for targeted muscle reinnervation surgery differed between improvement of prosthetic function (n = 19) and/or pain (n = 11). Functional outcome was evaluated with the Action Research Arm Test, the Southampton Hand Assessment Procedure, and the Clothespin-Relocation Test. Functional evaluation was performed at least at 6 months after final prosthetic fitting.

RESULTS

All nerve transfers were successful and provided independent myoelectric signals. The 10 patients available for final functional evaluation showed Action Research Arm Test scores of 20.4 ± 1.9 and Southampton Hand Assessment Procedure scores of 40.5 ± 8.1. The Clothespin-Relocation Test showed a mean time of 34.3 ± 14.4 seconds.

CONCLUSIONS

Targeted muscle reinnervation has improved prosthetic control and revolutionized neuroma treatment in upper limb amputees. Still, the rate of abandonment even after targeted muscle reinnervation surgery has been shown high, and several advances within the biotechnological interface will be needed to improve prosthetic function and acceptance in these patients.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, IV.

Pedicled Serratus Anterior Flap as an Alternative Muscle Target for Targeted Muscle Reinnervation in Transhumeral Amputees

Upper limb amputation is a universally devastating injury that results in substantial loss of function. Myoelectric prostheses represent a new generation of battery-powered programmable prostheses controlled by EMG signals. The aim of upper limb targeted muscle reinnervation (TMR) is to enhance the control of a myoelectric prosthesis by improving the number and quality of EMG signals that can be used to control prosthetic elbow, wrist, and hand movements. Current TMR techniques rely on preservation of parts of biceps and triceps to be used as reinnervated muscle targets. However, a subset of amputations exists in which the proximity or mechanism of injury results in loss of these local muscle targets, making these techniques less suitable. Alternative muscles beyond the zone of injury must be sought and imported as targets for residual nerves. Through its neurovascular anatomy and physical structure, the serratus anterior offers multiple potential targets in close vicinity to the upper limb, making the creation of additional signals through a single flap achievable in this challenging scenario. We present our technique using a pedicled serratus anterior muscle flap as an alternative muscle target in transhumeral amputees undergoing TMR.

Suprascapular Ligament Release From an Anterior Approach: An Anatomic Feasibility Study

PURPOSE

The results of spinal accessory to suprascapular nerve transfers have been less reliable than other nerve transfers in the upper limb, possibly owing to compression of the nerve by the suprascapular ligament. The posterior approach has been advocated to allow for release of the ligament. The purpose of this study was to determine whether a ligament release is possible from the anterior approach.

METHODS

Nine fresh-frozen cadavers were dissected to determine whether the ligament could be approached and released from the anterior approach. Complete ligament release was demonstrated by subluxation of the nerve out of the suprascapular notch.

RESULTS

Ligament release was achieved in all specimens, although in one, confirmation of complete release required a posterior approach.

CONCLUSIONS

Release of the suprascapular ligament to eliminate a potential source of compression of the suprascapular nerve during spinal accessory to suprascapular nerve transfer is possible through an anterior approach.

CLINICAL RELEVANCE

Release of the suprascapular ligament through an anterior approach allows this procedure to be performed through the same approach as brachial plexus exploration and spinal accessory nerve to suprascapular nerve transfer. This method could reduce surgical time and patient repositioning and avoid additional incisions.

Expanding traditional tendon-based techniques with nerve transfers for the restoration of upper limb function in tetraplegia: a prospective case series

BACKGROUND

Loss of upper extremity function after cervical spinal cord injury greatly affects independence, including social, vocational, and community engagement. Nerve transfer surgery offers an exciting new option for the reanimation of upper limb function in tetraplegia. The aim of this study was to evaluate the outcomes of nerve transfer surgery used for the reanimation of upper limb function in tetraplegia.

METHODS

In this prospective case series, we consecutively recruited people of any age with early (<18 months post-injury) cervical spinal cord injury of motor level C5 and below, who had been referred to a single centre for upper extremity reanimation and were deemed suitable for nerve transfer. All participants underwent single or multiple nerve transfers in one or both upper limbs, sometimes combined with tendon transfers, for restoration of elbow extension, grasp, pinch, and hand opening. Participants were assessed at 12 months and 24 months post-surgery. Primary outcome measures were the action research arm test (ARAT), grasp release test (GRT), and spinal cord independence measure (SCIM).

FINDINGS

Between April 14, 2014, and Nov 22, 2018, we recruited 16 participants (27 limbs) with traumatic spinal cord injury, among whom 59 nerve transfers were done. In ten participants (12 limbs), nerve transfers were combined with tendon transfers. 24-month follow-up data were unavailable for three patients (five limbs). At 24 months, significant improvements from baseline in median ARAT total score (34·0 [IQR 24·0-38·3] at 24 months vs 16·5 [12·0-22·0] at baseline, p<0·0001) and GRT total score (125·2 [65·1-154·4] vs 35·0 [21·0-52·3], p<0·0001) were observed. Mean total SCIM score and mobility in the room and toilet SCIM score improved by more than the minimal detectable change and the minimal clinically important difference, and the mean self-care SCIM score improved by more than the minimal detectable change between baseline and 24 months. Median Medical Research Council strength grades were 3 (IQR 2-3) for triceps and 4 (IQR 4-4) for digital extensor muscles after 24 months. Mean grasp strength at 24 months was 3·2 kg (SD 1·5) in participants who underwent distal nerve transfers (n=5), 2·8 kg (3·2) in those who had proximal nerve transfers (n=9), and 3·9 kg (2·4) in those who had tendon transfers (n=8). There were six adverse events related to the surgery, none of which had any ongoing functional consequences.

INTERPRETATION

Early nerve transfer surgery is a safe and effective addition to surgical techniques for upper limb reanimation in tetraplegia. Nerve transfers can lead to significant functional improvement and can be successfully combined with tendon transfers to maximise functional benefits.

FUNDING

Institute for Safety, Compensation, and Recovery Research (Australia).

Radial-to-Axillary Nerve Transfer Resolves Symptoms of Axillary Nerve Injury Due to Proximal Humerus Fracture-Dislocation in an Elderly Patient Treated With Hemiarthroplasty

Proximal humerus fractures in elderly patients are a common injury that can often be treated nonoperatively. However, surgery is indicated with some fracture patterns. Arthroplasty is an attractive option with poor bone quality, when there is a low likelihood of success with open reduction and internal fixation, and due to a timely return to function and weight bearing of the extremity in this patient population. A prerequisite for shoulder function for both native and replacement joints is a functional deltoid. Unfortunately, elderly patients with complex fracture patterns can sustain axillary nerve palsies that make management more difficult. The authors present a case of an elderly patient with a complex fracture-dislocation of the proximal humerus with traumatic axillary nerve palsy treated with hemiarthroplasty, followed by radial-to-axillary nerve transfer after the deltoid failed to improve. Congruency of the joint was restored and significant improvement in objective scoring metrics was achieved, making nerve transfer in this clinical scenario a viable option. [Orthopedics. 2019; 42(4):e395-e398.].