Brachialis to Anterior Interosseous Nerve Transfer: Comprehensive Anatomic Rationale

Abstract

BACKGROUND AND OBJECTIVES:

Distal nerve transfers for muscle reinnervation and restoration of function after upper and lower motor neuron lesions are a well-established surgical approach. The brachialis to anterior interosseous nerve (BrAIN) transfer is performed for prehension reanimation in lower brachial plexus and traumatic cervical spinal cord injuries. The aim of the study is to shed light on the inconsistent results observed in patients who undergo the BrAIN transfer.

METHODS:

An anatomic dissection was conducted on 30 fresh upper limb specimens to examine the intraneural topography of the median nerve (MN) in the upper arm at the level of the BrAIN transfer and the presence of intraneural fascicular interconnections distally.

RESULTS:

Fascicular interconnections between the AIN and other MN branches were consistently found in the distal third of the upper arm. The first interconnection was at 3.85 ± 1.82 cm proximal to the interepicondylar line, and the second one, after further proximal neurolysis, was at 9.45 ± 1.16 cm from the interepicondylar line. Intraneural topography of the AIN at the transfer level varied, with dorsomedial, dorsolateral, and purely dorsal locations observed.

CONCLUSION:

Consistent fascicular interconnections between the AIN and MN branches and intraneural topography variability of the MN may lead to aberrant reinnervation.

ABBREVIATIONS:

AIN

anterior interosseous nerve

Br

nerve branch to brachialis muscle

ECRB

extensor carpi radialis brevis

FDS

flexor digitorum superficialis

ICL

interepicondylar line

INIs

intraneural fascicular interconnections

MN

median nerve

PL

palmaris longus

PT

pronator teres.

Distal nerve transfers for muscle reinnervation and restoration of function after upper and lower motor neuron lesions are an established approach in a surgeon's repertoire.^1-3 After the first description by Lurje⁴ in 1948, the nerve branch to the brachialis muscle (Br) used as a donor for reanimation of radial^4-8 and median nerve (MN)-^6,9-11 innervated muscles has proven its expendability and versatility. The initially described nonselective neurotization of the whole MN in the antecubital fossa^9-11 was replaced by the more selective transfer to the anterior interosseous nerve (AIN) for restoration of prehension in lower brachial plexus injuries^6,12,13 and in traumatic cervical spinal cord injuries.^2,3,6,13-20 Despite its popularity, its efficiency remains still controversial with a wide range of clinical outcomes from poor to very good, not only among different studies but also in studies performed by the same surgical team.^{3,16,17,19,20} Different reasons such as long distance between the proximal nerve stump and the final target end plates, reduced selectivity in proximal transfers because of fascicular interconnections distal to the transfer site, anatomic inconsistency of the intraneural topography of the MN, and diverse time intervals from nerve injury to nerve transfer have been assumed to be responsible for this inconsistency.

Although the Br to AIN transfer has been examined in several anatomic studies regarding its feasibility, tension-free coaptation, and axonal count matching,^18,21 a comprehensive study on the fascicular interconnections distal to the coaptation site is still missing. Moreover, many authors have presumed the topographical consistency of the AIN in the posteromedial part of the MN at the level of the brachialis transfer,^2,12,16 despite no comprehensive study demonstrating its intraneural location and correlation with other MN motor fascicles.

We performed an anatomic dissection study to better understand the intraneural MN topography in the upper arm, examine the anatomic rationale behind this nerve transfer, and assess the following characteristics: (1) presence of fascicular interconnections between the AIN and other MN branches, (2) intraneural topography of the MN at the level of Br to AIN transfer, (3) feasibility of a tension-free nerve coaptation in relation to the fascicular interconnections, and (4) axonal matching between the donor Br and recipient AIN.

METHODS

Our Institutional Review Board has approved this study. Thirty fresh upper limb specimens were obtained from voluntary body donations to the Center for Anatomy. We microsurgically dissected the musculocutaneous nerve and MN and their muscle branches from their origin to the respective muscles' motor entry points in the upper arm and forearm. We used the interepicondylar line (ICL) connecting the medial and lateral humeral epicondyle as the bony landmark and a Vernier digital caliper (accuracy 0.01 mm) to measure distances. The upper arm was divided into 3 equal parts between the coracoid process and the medial humeral epicondyle. First, the ventral part of the MN in the upper arm was marked with an epineural nylon 6/0 stitch to ensure the correct orientation after further dissection. We then detached the pronator teres (PT) muscle from its insertion at the radius to identify and prepare all MN muscle branches. Dissection was performed under 3.5× loop magnification in a proximal to distal fashion by a single board-certified hand surgeon assisted by medical students. Comprehensive analysis of this nerve transfer's feasibility was performed by examining the following 4 different characteristics.

Presence of Fascicular Interconnections Between the AIN and Other MN Branches

Once the AIN was identified and carefully dissected from its origin to the target muscles, we documented any extraneural fascicular interconnections with other MN branches in the forearm and the distance of its origin level from the ICL. While applying slight tension to the nerve, we incised the epineurium with a 15-mm blade and microdissected the AIN using microscissors from distal to proximal. The distance of the first intraneural fascicular interconnections (INIs) to the ICL was measured, and intraneural dissection was continued until the level of the Br to AIN transfer is reached, which corresponds roughly to the junction of the proximal and middle third of the upper arm. Any further intraneural fascicular interconnection up until the level of the transfer was also noted.

Intraneural Topography of the MN at the Level of the Br to AIN Transfer

We transected the Br donor branch as close to the motor entry point as possible and performed the simulated nerve transfer to the AIN. We documented the intraneural topography of the AIN and other MN muscle branches (ventral, dorsal, medial, and lateral) at the theoretical level of the tension-free nerve coaptation.

Feasibility of a Tension-Free Nerve Coaptation of Br to the AIN in Relation to the Intraneural Fascicular Interconnections

The musculocutaneous branch to the Br was dissected from its origin to the motor entry point to achieve its maximum length to reach the AIN as distal as possible and thus overcome any INIs met more proximally. The feasibility of such a tension-free coaptation distal to the first INI was investigated.

Axonal Matching Between Donor (Br) and Recipient (AIN) Nerves

Nerve biopsies of the AIN and the Br nerve at the level of potential nerve transfer were obtained. Whenever possible, the Br nerve was harvested as a common trunk before its bifurcation or trifurcation to smaller branches entering the muscle. Then, samples were immersed in freshly prepared cold 4% paraformaldehyde in 0.1 M sodium phosphate buffer for up to 24 hours followed by being rinsed in sodium phosphate buffer for another 24 hours. After 2 hours of prefixation with 2% osmium tetroxide at room temperature, specimens were immersed in ethanol solutions of increasing concentrations, starting with 30% for 15-minutes each, followed by xylene clearing, wax infiltration, and paraffin-embedding.²² Semithin 4 μm cross-sections were stained with toluidine blue for 30 seconds and mounted with gelatin. Slide scanning was performed with a Vectra® Polaris™, and myelinated axon quantification was conducted with a semiautomatic protocol using Fiji-Freeware, as published elsewhere.²³ Anatomic and histomorphometric obtained data are presented as “mean ± SD.”.

RESULTS

Fascicular Interconnections Between AIN and Other MN Fascicles

Intraneural fascicular interconnections of the AIN to other MN fascicles were always present in the distal third of the upper arm, most commonly between the flexor digitorum superficialis (FDS) and palmaris longus (PL) fascicles (12/30 specimens). The first INI met during proximal AIN dissection was at 3.85 ± 1.82 cm proximal to the ICL, whereas after further proximal neurolysis, the second INI was found at a mean distance of 9.45 ± 1.16 cm from the ICL. Distal to the ICL and proximal to the AIN origin from the MN, we found no INI with other motor or sensory fascicles (Figures 1-4). The origin of the AIN in the forearm was recorded at 5.08 ± 1.54 cm distal to the ICL. Extraneural fascicular interconnections of the AIN were observed in only one specimen, which was with the proximal nerve branch to the FDS 3 cm distal to the ICL. The results are shown in Table 1.

FIGURE 1.

Preparation of the median nerve branches in the forearm. AIN, anterior interosseous nerve; FCR, flexor carpi radialis fascicle; FDS, flexor digitorum superficialis fascicle; PT, pronator teres fascicle.

FIGURE 4.

Measurement of the height of fascicular interconnections using as landmark the interepicondylar line (dashed line).

TABLE 1.

Measurements of the AIN's Level of Origin and the Presence and Level of the First and Second Intraneural Fascicular Interconnections After Proximal Neurolysis and Intraneural Topography of the AIN in the Median Nerve in the Middle/Distal Third of Upper Arm

Upper limb number/side	Distance origin of AIN to ICL (cm)	Distance of first INI from AIN to ICL (cm)	Distance of second INI from AIN to ICL (cm)	Comments	Location AIN
1R	NM	4.3	9.6	AIN common fascicle with FCR, no PL	DM
1L	NM	4.9	10.1	INI with FCR, no PL	DM
2R	NM	2.6	6.9	First INI with FDS, second INI with FCR, no PL	DM
2L	NM	2	11	ENI with FDS 3-cm distal ICL, first INI with FDS, AIN same fascicle with FDS, no PL	DM
3R	NM	4	11	AIN next to common fascicle FCR/PL	DM
3L	NM	6.5	10.5	AIN next to common fascicle FCR/PL	DM
4R	−2.6	3.8	NM	Common fascicle with FCR/PL	DL
4L	−1.9	2	NM	First INI with FDS, AIN common fascicle with FDS	DM
5R	−5.8	3.6	9	First INI with common fascicle FDS/PL	DL
5L	−5.3	2.9	9	First INI with common fascicle FDS/PL	DL
6R	−7.6	2.7	NM	None	DL
6L	−8	3.8	9.8	First INI with common fascicle FDS/PL	DL
7R	−4.7	3	NM	No PL	DL
8L	−4.2	3.6	NM	FCR, PL, FDS as common fascicle at anterior part	D
9R	−6.7	4.6	9	An extra INI through a twig with FDS at the ICL level	DL
9L	−4.6	5.6	10.5	First INI with common fascicle FDS/PL	DM
10R	−7.3	1.7	8.5	None	DL
10L	−4.6	3	11.2	None	D
11R	−5	2.4	9.9	No PL	D
11L	−3.8	3.5	10.3	No PL	DM
12R	−3.6	8.1	8.9	First INI with common fascicle FDS/PL	DM
12L	−3.8	5.4	8.3	First INI with common fascicle FDS/PL	DM
13R	−5.8	4.8	8.1	PT/FCR common fascicle proximal to ICL, no PL	D
13L	−4.9	6.7	9.5	Origin FCR at the ICL level, PT/FCR common fascicle, no PL	D
14R	−6.1	1.5	9.8	FDS/PL common fascicle proximal to ICL	D
14L	−3.6	0	7	First INI with FDS/PL common fascicle at the ICL level, PT/FCR common fascicle	DL
15R	−5.2	7.2	NM	None	DL
15L	−4.3	5.4	10.8	FDS/PL common origin trunk at the ICL level	D
16R	−7	3.7	9.2	FDS/PL common fascicle	D
16L	−5.7	2.4	9.1	FDS/PL common fascicle	D
Mean (±SD)	5.08 (±1.54)	3.85 (±1.82)	9.45 (±1.16)	NA	11/30 DM 10/30 DL, 9/30 D

AIN, anterior interosseous nerve; D, dorsal; DL, dorsolateral; DM, dorsomedial; ENI, extraneural fascicular interconnections; FCR, flexor carpi radialis nerve branch; FDS, flexor digitorum superficialis nerve branch; ICL, interepicondylar line; INI, intraneural fascicular interconnections; L, left; NA, not applied; NM, not measured; PL, palmaris longus nerve branch; PT, pronator teres nerve branch; R, right.

Negative values indicate measurement distal to the ICL.

FIGURE 2.

Intraneural neurolysis of median nerve fascicles in a retrograde way from distal to proximal and dissection of the brachialis motor branch (proximal white vessel loop) branching from the musculocutaneous nerve (yellow vessel loop). AIN, anterior interosseous nerve; FCR, flexor carpi radialis fascicle; PT, pronator teres fascicle. Dashed line: interepicondylar line.

FIGURE 3.

After proximal intraneural dissection and neurolysis of different median nerve branches, a fascicular interconnection of the AIN with the FCR branch was noted (asterisk). More proximally, a second bundle of fascicular interconnections was revealed (star). Note that at the level of theoretical BrAIN transfer, the bundle of fascicular interconnections can hardly be overcome for a tension-free coaptation. AIN, anterior interosseous nerve; FCR, flexor carpi radialis fascicle; PT, pronator teres fascicle.

Intraneural Topography of the MN at the Level of the Br to AIN Transfer

We documented the intraneural AIN location at the level of a tension-free Br to AIN coaptation. The MN fascicles' topography at that level—which was not at a constant distance from the ICL—revealed the AIN to be dorsomedial in 13/30 specimens, dorsolateral in 11/30 specimens, and purely dorsal in 9/30 specimens. The branch to the PT was found ventrally in all cases, and the proximal FDS branch had a common fascicle with the PL in 12/30 cases, whereas there was no PL muscle in 9/30 specimens. The flexor carpi radialis branch formed a common fascicle with the PT branch in 21/30 cases. The sensory branches were located centrally in the nerve. Schematic representations of different intraneural topography patterns are demonstrated in Figure 5.

FIGURE 5.

Schematic presentation of different anatomic patterns of intraneural topography of the median nerve around the level of the coaptation site with the brachialis branch. AIN, anterior interosseous nerve; FCR, flexor carpi radialis fascicle; FDS, flexor digitorum superficialis fascicle; PL, palmaris longus fascicle; PT, pronator teres fascicle. The fascicles in gray represent the sensory branches. D, dorsal; L, lateral; M, medial; V, ventral.

Consistent Intraneural Fascicular Interconnections Impeded a Tension-Free Br to AIN Transfer Distal to Them

A tension-free coaptation of the Br to AIN distal to any INI was possible in only 3 of 30 upper limbs (12R, 13L, 15R). In 27 of 30 specimens, the distal fascicular interconnections could not be overcome without the use of a nerve graft. By continuing the proximal dissection until the second INI was identified, a tension-free nerve transfer distal to it was consistently achievable, except in one limb (2R), where epineural coaptation was only possible with some tension.

Donor-To-Recipient Axon Count Ratio at the Nerve Transfer Level was 0.55 ± 0.27

Axon quantification was possible in 24/30 brachialis nerve branches and in 22/30 AINs because of technical issues (suboptimal paraffin-embedding). The nerve to the Br contained 1198 ± 464 myelinated axons, and the AIN contained 2327 ± 742 myelinated axons at the level of the transfer. The histological samples stained with toluidine blue are depicted in Figure 6. The average ratio of myelinated axons of the donor and recipient nerve as calculated by paired comparison within the same limb was 0.55 ± 0.27, whereas limbs with missing values for Br or AIN were excluded from ratio calculation. Detailed results are presented in Table 2.

FIGURE 6.

Semithin 4-μm cross-sections prefixed with osmium tetroxide 2% and stained with toluidine blue. A, Anterior interosseous nerve; B and C, nerve to brachialis muscle right and left. Scale bar: 100 µm, Magnification 20×.

TABLE 2.

Myelinated Axon Quantification of the Nerve to the Brachialis Muscle and the Anterior Interosseous Nerve at the Level of the Nerve Transfer in the Upper Arm

Upper limb number/side	Axon count of brachialis	Axon count of AIN	Ratio of Br/AIN
1R	868	Excluded	NA
1L	935	3301	0.28
2R	698	3274	0.21
2L	Excluded	2973	NA
3R	Excluded	Excluded	NA
3L	660	3058	0.22
4R	Excluded	Excluded	NA
4L	1283	1902	0.67
5R	509	2812	0.18
5L	1526	1701	0.90
6R	887	2811	0.32
6L	687	1563	0.44
7R	1123	2546	0.44
8L	619	1497	0.41
9R	1302	1306	1.00
9L	1363	Excluded	NA
10R	Excluded	1272	NA
10L	2029	3947	0.51
11R	1331	Excluded	NA
11L	1943	Excluded	NA
12R	1134	2335	0.49
12L	679	Excluded	NA
13R	Excluded	3141	NA
13L	1015	1889	0.54
14R	1606	Excluded	NA
14L	Excluded	1929	NA
15R	1489	1646	0.9
15L	1241	2168	0.57
16R	2094	2044	1.02
16L	1734	2098	0.83
Mean (±SD)	1198 (±464)	2328 (±742)	0.55 ± 0.27

AIN, anterior interosseous nerve; Br, nerve branch to brachialis muscle; L, left arm; NA, not applied; R, right arm.

DISCUSSION

In this study, we conducted a comprehensive and systematic examination of the number and level of fascicular interconnections between the AIN and other MN branches. Our aim was to gain insights into the underlying cause of inconsistent or poor results of the brachialis to AIN transfer when a proximal coaptation in the upper arm is selected.^{3,16,17,19,24} The prevailing belief that the AIN fascicle is consistently located posteromedially is not supported by our findings. Moreover, we observed constant INIs distal to the level of the brachialis to AIN nerve transfer, which may result in axonal dispersion and a reduced axonal load reaching the target muscle. These insights contribute to understanding the variable clinical outcomes associated with the brachialis to AIN nerve transfer. Consequently, we recommend that, during this procedure, the AIN should be dissected from distal to proximal up to the coaptation level to ensure a more effective transfer. Bertelli et al¹⁷ performed a direct transfer of the Br to AIN in 5 spinal cord injury patients. Only one patient achieved M3 finger flexion strength, whereas the other 4 achieved only M0 to M2. In other 3 patients in that study, the AIN was first located distally and then dissected proximally. By sacrificing the INI to reach the donor Br, all 3 patients achieved functional grip strength (1 M3, 2 M4). This approach seems to be more reliable and leads to more predictable outcomes also in accordance with our findings. Nevertheless, possible drawbacks could be the risk of intraneural scar formation and the sacrifice of motor branches that may be important for an already impaired hand function. Another study reported the use of an in situ vascularized nerve graft to bridge the brachialis donor nerve proximally with the AIN in the forearm, aiming to overcome the risk of collateral axon loss and nonselective reinnervation, but half of the patients achieved only M0-M2 for flexor pollicis longus and flexor digitorum profundus 2-3 muscle strength.²⁰

Other authors have alternatively used the brachioradialis nerve branch as the donor for the AIN reinnervation in brachial plexus or spinal cord injuries resulting in poor outcomes.^17,25 This could be related to the significantly lower donor-to-recipient axon count ratio (0.24)²⁶ compared to that of the brachialis nerve branch to AIN (0.55 ± 0.38 the study by Sananpanich et al,¹⁸ 0.55 ± 0.27 our results) for approximately the same distance to the target muscles. Interestingly, when the nerve branch to the extensor carpi radialis brevis (ECRB) was used as the donor in tetraplegic patients, better functional outcomes were consistently achieved,^3,17 despite a similarly low donor-to-recipient axon count ratio as the brachioradialis to AIN transfer (0.24 ± 0.15).¹⁸ Consequently, superiority of the ECRB as the donor may be associated with the predictable and clear path of donor axons distal to fascicular interconnections and to the proximity to the target end plates. In addition, mechanical and cognitive synergy for finger/thumb flexion during ECRB activation is another key factor that may explain its success. Other important parameters that are relevant for the final result such as time from nerve injury to reinnervation, status of muscle atrophy, and articular stiffness have to be taken into consideration as well. Ultimately, it is crucial to consider the time that has passed from the surgery to the final follow-up, given that obtaining a plateau outcome in the brachialis nerve to AIN transfer usually requires an extended period, often surpassing 24 months.³

Another contributing factor for compromised selectivity may be the inconsistency of the intraneural topography of the MN at the nerve transfer level. In previous studies, a dorsomedial location of the AIN in the junction of the middle/lower upper arm was mentioned,^2,3,15-18 probably based on findings during intraoperative fascicle stimulation. In cases of traumatic cervical spinal cord injury with a still intact AIN motor neuron pool in the spinal cord, intraoperative stimulation of the recipient AIN is possible, even many years after injury. However, in brachial plexus injuries or in spinal cord injuries with simultaneous lesion of the lower motor neuron, this helpful tool loses its utility. In the literature, we could only identify 2 anatomic studies that thoroughly examined the MN intraneural topography in the upper arm, but results were inconclusive and unspecific.^13,14 We performed a systematic investigation of the intraneural location of the AIN in the MN specifically at the level of theoretical Br nerve transfer. In our specimens, the AIN location was exclusively dorsomedial in one third, dorsolateral in another third, and purely dorsal in the remaining third. Our findings of possible dorsolateral localization of the AIN at that level confirm those of a previous study on high-resolution magnetic resonance neurography in spontaneous anterior interosseous syndrome.²⁷ However, another recent magnetic resonance neurography study revealed a dorsomedial location of the AIN.²⁸ The only comprehensive analysis we found so far in the literature is the colossal work of Sir Sunderland,²⁹ where the AIN localization 10 cm proximal to the ICL was described in the dorsolateral rather than the dorsomedial part of the MN. An additional anatomic study also examined the AIN location at that level, but the findings only indicate a dorsal position without providing any further specification.³⁰ We assume that this variability may be explained by the AIN migration from a dorsomedial position in the proximal arm to a dorsolateral position in the forearm combined with the varying level of the Br to AIN transfer. The migrating and variable intraneural location of the AIN at the level of the nerve transfer to the brachialis branch has significant implications for the reverse nerve transfer procedure as well, such as reinnervating the brachialis motor branch with MN fascicles in upper brachial plexus injuries. It is essential to proceed with caution when dissecting the MN fascicles and to use low-intensity electrical stimulation carefully to avoid injuring the dorsally located AIN.

Our results of myelinated axon quantification of the AIN and brachialis nerve at the level of the transfer align with previously published data. In our study, the AIN contained 2327 ± 742 and the nerve to Br contained 1198 ± 464 myelinated axons, resulting in a ratio of 0.55 ± 0.27. Sananpanich et al¹⁸ reported 2903 ± 1049 myelinated axons for the AIN and 1497 ± 606 for the brachialis nerve branch with a ratio of 0.51, whereas Ziaziaris et al²¹ found 1760 ± 638 myelinated axons for the AIN and 944 ± 581 for the brachialis nerve with a ratio of 0.53. In another study where the brachioradialis nerve branch was used as a donor,²⁶ the AIN myelinated axon count was reported to be 2266.7 ± 274.8. While the absolute numbers may differ among studies, likely because of variations in staining and counting methods, the ratio appears to be relatively constant.

Limitations

The limb size in relation to the body size and the cross-sectional area of the Br and AIN at the coaptation level were not measured.

CONCLUSION

The efficiency of transferring the brachialis nerve branch to the AIN for prehension reanimation remains a subject of debate and may be related to unexplored anatomic variability. We revealed consistent fascicular interconnections between the AIN and other MN branches and variability in the intraneural topography of the AIN on the transfer level. The dogma that the AIN fascicle is located posteromedially is not consistent at all, whereas constant INIs distal to the brachialis to AIN nerve transfer level may lead to axonal dispersion and reduced axonal load to target muscle. The current findings shed light on the unpredictable clinical outcomes of the brachialis to AIN nerve transfer and suggest that, during the performance of this transfer, it is advisable to dissect the AIN from distal to proximal up to the coaptation level.

Funding

This study was financed by the Clinical Research Grant 2020 provided by the Federation of European Societies for Surgery of the Hand/Foundation for Hand Surgery.

Disclosures

The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article.

Confirmation of authorship, contributorship, and acknowledgements.

All aforementioned authors made a substantial contribution and meet the authorship criteria according to the “International Committee of Medical Journal Editors (ICMJE) authorship guidelines.”

COMMENTS

This study provides an anatomic rationale for the BrAIN transfer and examines factors contributing to successful reanimation. Anatomic dissections were performed on 30 fresh upper limb specimens to analyze the intraneural topography of the median nerve in the upper arm at the BrAIN transfer level, where INIs were found in 90% (27/30) of the specimens, which interfered with a tension-free transfer. These findings emphasize the significance of intraneural anatomy, as nerve fascicles are not linear tubes, but rather a woven cable with interconnections between fascicles.

The fascicular topography of major nerves, for example, the median nerve can vary along the length of the arm, and this variation can significantly affect nerve transfers, and thus, may account for the unpredictable clinical outcomes of the BrAIN transfer, in particular. Moreover, the arrangement of fascicles at a specific location in a nerve may not be identical between individuals because of the exchange of axons between fascicles. Therefore, these procedures should not be considered straightforward cases.^1a

One major challenge is the anatomic inconsistency of the median nerve's intraneural topography also contributes to this inconsistency. To address these issues, the authors suggest dissecting the AIN from distal to proximal up to the coaptation level during the transfer until locating the second intraneural interconnection with acceptable axonal matching, which could improve outcomes.

While this approach could alleviate tension, there is a risk of extensive intraneural scarring resulting from the intraneural dissection. An alternative strategy could involve placing a small graft or conduit between the 2 nerves (Br and AIN) instead of intensive dissection to achieve a tension-free coaptation. For instance, harvesting the medial or lateral antebrachial cutaneous nerve to bridge the gap might be a viable option. Future studies could compare the outcomes of these 2 methods—dissection only vs transfer with grafting—to determine the most effective approach.

Given the difficulties in translating findings from cadaveric dissection studies to address all clinical questions, the anatomic research by the authors reveals many aspects of the BrAIN procedure. It offers a valuable explanation for the variable outcomes observed and provides essential baseline knowledge for future research.

Loay Shoubash and Mark A. Mahan

Salt Lake City, Utah, USA