Anatomic Study of the Innervation of Extensor Carpi Radialis Longus and Extensor Carpi Radialis Brevis. Interest in Nerve Transfers

Abstract

Objective

This study pretends to describe the innervation pattern of Extensor Carpi Radialis Longus (ECRL) and Extensor Carpi Radialis Brevis (ECRB) to use ECRL branches as a first choice in nerve transfers to restore flexion and extension of wrist and fingers due to its easier identification and its redundant innervation.

Methods

Nine cryopreserved and anonymous specimens were dissected to identify the radial nerve and describe its number of branches, the distance between its origin and a line connecting both epicondyles, the length of each branch, and the type of innervation of ECRL and ECRB according to Taylor's classification.

Results

Six out of nine specimens presented two branches from the radial nerve to innervate the ECRL (Taylor type 3). Three out of nine specimens only had one branch to innervate the ECRL, originating from the radial nerve (two of them classified as a Taylor type 1 and the other as a Taylor type 2). All the specimens had only one branch to innervate the ECRB (eight showing a Taylor type 1 pattern, and one classified as Taylor type 2); in seven out of nine, this branch emerges from the deep branch of the radial nerve, emerging in the other two specimens from the superficial branch of the radial nerve.

Conclusion

The use of the ECRL branches could be considered the first choice in nerve transfers to restore the flexion and extension of the elbow, wrist and fingers in nerve injuries, because of its constant origin after the brachioradialis branch and in most of the cases its redundant innervation.

Level of evidence: VI

 

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Keywords

anatomy - nerve injury - brachial plexus - nerve transfers

Introduction

Nerve transfers as a treatment for nerve injuries, either at the level of the brachial plexus or the terminal branches, are gaining popularity due to its excellent results in the restoration of muscular function. To restore the extension of the wrist and fingers in radial nerve injuries, nerve transfers from the median to radial nerve are the most commonly used, transferring median nerve branches to the flexor digitorum superficialis (FDS), flexor carpi radialis (FCR) and palmaris longus (PL) to radial nerve branches to the extensor carpi radialis brevis (ECRB) and posterior interosseous nerve (PIN).[1] Although there is little literature regarding the use of nerve branches to the ECRL in nerve transfers, in the last 10 years some authors reported its potential in this field according to its anatomical characteristics and easier identification in comparison with other alternatives as branches to the ECRB. Charlotte Waxweiler et al.[2] describe the use of the branch to the ECRL in nerve transfers from the brachioradialis (BR) to the ECRL in the spastic upper limb to reduce spasticity and recover extension of the wrist. Antonio Garcia-López[3] et al. described a nerve transfer to restore wrist extension in radial nerve palsy or posterior cord lesions using the pronator teres (PT) branch from the median nerve to the ECRL branch. Regarding the excellent results achieved in the mentioned studies, we anatomically characterize the branches of the radial nerve to the ECRL and ECRB to determine if there is redundant innervation and if there is variance in its origin. In our study, we describe the innervation pattern of the ECRL and ECRB according to its origin and number of branches, its distance of emergence to a line connecting both epicondyles, the length of these branches, and the type of innervation according to Taylor's classification[4] ([Table 1]) to use it as a first choice in nerve transfers for the restoration of flexion and extension of the elbow and wrist and fingers.

Table 1 Specimen's demographics

Specimen's demographics
Specimen	Sex	Age	Laterality
1	Male	79	Left
2	Male	87	Left
3	Female	81	Left
4	Male	79	Left
5	Female	91	Right
6	Male	80	Left
7	Male	78	Right
8	Female	90	Right
9	Male	76	Left

 

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Methods

This is an anatomical descriptive study to characterize the branches of the radial nerve to the ECRL and ECRB. Nine cryopreserved and anonymous specimens ([Table 1]) were dissected with magnifying loops x4.2 to identify the branches emerging from the radial nerve. The incision was made over the interval between the brachialis and the brachioradialis. After the radial nerve was identified in this interval, using blunt dissection we exposed the branches emerging from the radial nerve from proximal to distal, taking as the proximal limit the last branch to the BR and the distal limit the entrance of the deep branch of the radial nerve into the Froshe's arcade. We registered where the ECRL and ECRB branches emerged from, especially if the ECRB branches originated from the superficial or deep branch of the radial nerve, and evaluated the number of branches for the ECRL and ECRB. We measured the distance between the emergence point of each mentioned branch to a line connecting the two epicondyles (intercondylar line), getting negative values if the measure was proximal to the line and positive if they were distal to it. We also measured the length of each branch from its emergence point to its entry into the muscle and the type of innervation according to Taylor's classification[4] ([Table 2]). All measures were taken with a surgical calibrated ruler (Devon©). Photographical record was done for all the specimens.

Table 2 Taylor's Muscle Nerve Classification

Taylor's Muscle Nerve Classification
Type I	Muscle supplied by single motor nerve that divides after entering the muscle.
Type II	Muscle supplied by a single motor nerve that divides before entering the muscle.
Type III	Muscle supplied by multiple nerve branches that originate from the same motor nerve trunk.
Type IV	Muscle supplied by multiple motor nerves that originate from different nerve trunks.

 

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Results

In all nine specimens, we dissected the radial nerve and individualized its motor branches to the ECRL and ECRB.

Six out of nine specimens presented two branches to innervate ECRL emerging both from the radial nerve after the distal branch to the BR and before the bifurcation into superficial and deep branches ([Fig. 1a]), except for one specimen where the distal branch emerged from the deep branch of the radial nerve ([Fig. 1b]). Three specimens had only one motor branch for the ECRL emerging from the radial nerve.

Fig. 1 a ECRL innervated by two motor branches (arrowheads) from the radial nerve and ECRB innervated by one motor branch (arrow) from the deep branch of the radial nerve. RN: radial nerve, db: deep branch, sb: superficial branch, BR: brachioradialis, ECRL: extensor carpi radialis longus, ECRB: extensor carpi radialis brevis [Figure 1b] ECRL innervated by two motor branches (proximal arrowhead) one arising from the radial nerve and the other from the deep branch (distal arrowhead) of it, and ECRB innervated by one motor branch (arrow) from the deep radial nerve branch. RN: radial nerve, db: deep branch, sb: superficial branch, BR: brachioradialis, ECRL: extensor carpi radialis longus, ECRB: extensor carpi radialis brevis

All specimens except one presented the origin of the motor branches to the ECRL before the nerve crossed the intercondylar line. The measured mean point of origin was -17,73mm ± 13,04. If we measure the mean point of origin only accounting for the specimens with two branches to ECRL, we obtain that the mean emergence points for the proximal and distal branches at -26,33mm ± 10,05 and -11,67mm ± 7,31 respectively.

Regarding its type of innervation according to Taylor's classification, we classified the specimen with two branches to the ECRL as a Taylor type 3, two specimens with one motor branch to ECRL were classified as Taylor type 1, and one specimen was classified as Taylor type 2 ([Table 3]).

Table 3 ECRL innervation characteristics including: the specimen, number of branches, origin of motor branches, distance from the origin to the intercondylar line, length from its origin to the entrance into the muscle and Taylor type

ECRL
Specimen	Number of branches	Origin	Distance (mm)	Length (mm)	Taylor type
1	2	Radial nerve	-28	20	3
			-10	31
2	2	Radial nerve	-16	36	3
			-7	42
3	2	Radial nerve	-24	60	3
		Deep branch of radial nerve	-7	50
4	1	Radial nerve	-17	36	1
5	1	Radial nerve	10	43	1
6	2	Radial nerve	-15	36	3
			-6	55
7	2	Radial nerve	-35	37	3
			-15	66
8	1	Radial nerve	-31	57	2
9	2	Radial nerve	-40	50	3
			-25	48

All specimens only had one motor branch to the ECRB. We found variability in its origin, emerging in seven specimens from the deep branch of the radial nerve ([Fig. 2]), just before its division into the supinator motor branches and its entry into the Frohse's arcade, and in two specimens emerging from the superficial branch ([Fig. 3]).

Fig. 2 ECRL innervated by one motor branch (arrowhead) arising from the radial nerve, ECRB innervated by one motor branch (arrow) from the deep branch of the radial nerve. RN: radial nerve, db: deep branch, sb: superficial branch, BR: brachioradialis, ECRL: extensor carpi radialis longus, ECRB: extensor carpi radialis brevis.

Fig. 3 ECRL innervated by one motor branch (arrowhead) arising from the radial nerve, ECRB innervated by one motor branch (arrow) from the superficial branch of the radial nerve. RN: radial nerve, db: deep branch, sb: superficial branch, BR: brachioradialis, ECRL: extensor carpi radialis longus, ECRB: extensor carpi radialis brevis.

In all the specimens the motor branch to the ECRB emerged distal to the intercondylar line, with a mean distance of 23,89mm ± 8,37.

All specimens were classified as Taylor type 1, except for one specimen that was classified as Taylor type 2 ([Table 4]).

Table 4 ECRB innervation characteristics including: the specimen, number of branches, origin of motor branches, distance from the origin to the intercondylar line, length from its origin to the entrance into the muscle and Taylor type

ECRB
Specimen	Number of branches	Origin	Distance (mm)	Lenght (mm)	Taylor type
1	1	Deep branch of radial nerve	20	30	1
2	1	Deep branch of radial nerve	12	55	1
3	1	Deep branch of radial nerve	24	45	1
4	1	Superficial branch of radial nerve	26	55	1
5	1	Superficial branch of radial nerve	31	60	1
6	1	Deep branch of radial nerve	39	47	2
				33
7	1	Deep branch of radial nerve	25	66	1
8	1	Deep branch of radial nerve	13	76	1
9	1	Deep branch of radial nerve	25	87	1

We measured the length of each motor branch to ECRL, and ECRB to estimate with further studies the possibility of a tension-free nerve transfer. For the motor branches to the ECRL we obtained a mean length of 44,47mm ± 12,26, measuring both the proximal and the distal branches apart we obtained a mean length of 37,80mm ± 13,72 and 48,67mm ± 11,83 respectively. In reference to the motor branch to the ECRB we obtained a mean length of 55,40 ± 17,90 from its emergence point to its entrance into de muscle belly.

 

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Discussion

In this study, we describe the innervation pattern of ECRL and ECRB to use its branches in nerve transfers for restoration of flexion and extension of the wrist and elbow. Hyejin Cho, et al.[5] reported the ECRL was innervated by one branch from the radial nerve in 70% of the specimens, by two branches in 27,5%, and by three branches in 2,5% of them; in all the specimens above the intercondylar line. We describe that the ECRL has double innervation from the radial nerve in six out of nine (66,7%) specimens, finding a higher incidence of redundant innervation in our specimens. This redundant innervation allows the use of one of these branches to restore flexion or extension of the wrist or elbow depending on the nerve transfer, without a total loss of function of the ECRL when using it as a donor. Classically nerve transfers reported in the literature for the restoration of flexion and extension of the wrist did not include the branches of the radial nerve to the ECRL either as donors or receptors. Antonio Garcia-López et al.[3] described the use of the ECRL branches as receptors in the restoration of wrist extension, using a nerve transfer from pronator teres branches to ECRL branches and FCR branch to the PIN. They advocate for the ECRL instead of the ECRB branch because of its easier identification, in specimens where the ECRB branch arises from the deep branch of the radial nerve it can easily be confused with the PIN, or even with the supinator branches. As we mentioned before, Charlotte Waxweiler et al.[2] describes the use of ECRL in nerve transfers using a branch from the BR to the ECRL to reduce spasticity and recover the extension of the wrist. They found a single motor branch innervating the ECRL in 70% of the specimens and two branches in 30% of cases, a lower percentage of redundant innervation than we found. As we also found, they mention that all ECRL branches originated distally from the BR nerve branches. Jan Fridén and Andreas Gohritz[6] reported a case of nerve transfer from brachialis motor nerve to an ECRL nerve branch for restoration of wrist extension in a patient with C5 tetraplegia with conservation of elbow flexion by biceps brachialis (C5/6) and brachialis muscles (C5/6/7) and abolition of wrist extension but without ECRL denervation (C5/6) with good clinical results (M3 strength of wrist extension) by five months after surgery. Regarding its use as a donor, we didn't find any reports in the literature. As we reported, its anatomical location proximal to the intercondylar line allows it to be a potential donor for nerve transfer to musculocutaneous nerve branches in the restoration of elbow flexion, without a complete loss of function of the ECRL due to its redundant innervation.-Regarding ECRB innervation, we found in concordance with Hyejin Cho, et al,[5] that ECRB was only innervated by one nerve branch in all the specimens. The use of the ECRB branch for nerve transfer is well-reported in the literature. It's commonly used for median to radial nerve transfers in the restoration of wrist and finger extension, but it's also reported its used as a donor in the restoration of pronation of the forearm using PT branches as receptors.[1] [7] [8] Classically for median to radial nerve transfer it is used FDS nerve to ECRB nerve and FCR nerve to PIN because of its synergistic function.[8] [9] Koji Sukegawa, et al[10] and Ukrit et al[9] reported the feasibility of the median to radial nerve transfer from the FDS nerve to the ECRB nerve. They reported that the stump of the FDS branch reached the ECRB nerve branch without tension in all the specimens they studied, and reported that the number of axons in the FDS nerve branch was superior to 30% of axons of the ECRB needed for the nerve transfer to be functional.[11] [12] Additionally, in our study we reported two branching patterns: the ECRB branch originating from the deep branch of the radial nerve or its superficial branch. Knowledge about the ECRB branching pattern is of interest to allow for easier location of these branches to use as donors for nerve transfers. These results also suggest that injury in the superficial branch of the radial nerve can be accompanied by ECRB paralysis.

 

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Conclusion

To conclude, we reported different patterns of ramification of the radial nerve to innervate the ECRL and ECRB, finding three different patterns for the ECRL and two for the ECRB. We described its anatomical characteristics regarding its origin and length to easily identify them to its use as nerve transfers. We describe both ECRL and ECRB are reasonable options to undergo nerve transfer either as donor or recipient nerve. ECRB nerve transfer is already established for the median to radial nerve transfer, so we described its anatomic parameters to facilitate its identification. We also reported the potential of ECRL motor branches to be used as a donor or receptor in nerve transfers for the restoration of flexion/extension of elbow and wrist due to its constant origin after the BR motor branches and, in most cases, its redundant innervation.

 

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Conflicto de los intereses

Ninguno de los autores, su familia inmediata y cualquier fundación de investigación a la que estén afiliados recibieron pagos financieros ni otros beneficios de ninguna entidad comercial relacionada con el tema de este artículo.

Ethics Approval

The study was performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki.

Author's Contributions

All authors contributed equally to this work. All authors contributed to the study conception and design, material preparation, data collection, and analysis. The first draft of the manuscript was written by Pablo Martínez Collado and Rosa Morro Martí.

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Publikationsverlauf

Eingereicht: 02. Juli 2024

Angenommen: 24. März 2025

Artikel online veröffentlicht:
21. Juli 2025