The internal anatomy of the median nerve in the region of the elbow The internal anatomy of the median nerve in the region of the elbow has been studied by microdissection in 20 cadavers. Gross branching patterns were studied in an additional 14 cadavers. There are four major branches or branch groups: I to pronator teres, II to flexor carpi radialis, flexor digitorum superticialis, and palmaris longus; III to the anterior interosseous nerve; and IV to flexor digitorum superficialis. Three of these could be traced proximally within the main trunk of the median nerve, the average being I - 10 cm; III - 7.5 cm; IV - 2 cm. This information should have clinical applications in repair and grafting of the median nerve near the elbow and in understanding clinical nerve compression syndromes. (J HAND SURG 1992;17A648-56).
Stephen F. Gunther, MD, Doreen DiPasquale, MD, Washington, D.C., LCDR Robert Martin, MC, USN, Bethesda, Md.
T
his study of the internal anatomy of the median nerve in fresh and fresh frozen human cadavers was prompted by two unusual cases of median neuropathy above the elbow. A search of the literature revealed that little has been published on the gross anatomy of median nerve branching near the elbow, and even less on the internal anatomy. Although current texts give general descriptions of branching patterns, one must go back to the works of Linell’ in 1921 and Sunderland and Ray’ in 1946 for accurate and detailed descriptions. Sunderland is credited with demonstrating that axons travel from one fascicle to another along the course of
From the Departments of Orthopaedic Surgery of the Washington Hospital Center and George Washington University, Washington, D.C., and the Anatomical Teaching Laboratory of the Uniformed Services University of Health Sciences, Bethesda, Md. This work was presented at the annual meeting of the American Society for Surgery of the Hand in Seattle, Wash., Sept. 24, 1990. It was awarded the Emmanuel B. Kaplan Prize by the New York Hand Society. Received for publication July 17, 1991.
May 24, 1990; accepted
in revised form
No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Reprint requests: Stephen F. Gunther, MD, Washington Hospital Center, Department of Orthopaedic Surgery, 110 Irving St., NW, Washington, DC 20010. 311132566
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and
a nerve, and he also pointed out that this interchange may cease near large joints, where fascicles sometimes remain autonomous for certain distances before separating off to form branches. Only Sunderland3.4 and Jabaley et al.’ have reported studies of the internal topography of the median nerve in the region of the elbow. Between them, they have reported fewer than five specimens. The specimens were studied principally by means of serial histologic sections, which in Jabaley’s study did not go above the elbow. Although helpful and stimulating, these few reports did not completely answer our questions as to how similar nerve lesions above the elbow could cause different clinical syndromes. Therefore the median nerve was studied above and below the elbow by gross and microdissection techniques in fresh cadavers. Material and methods Thirty-two unpreserved cadaver arms, mostly fresh frozen and thawed, were used in this study. The first nine dissections studied the surroundings of the median nerve and its arrangement into anterior and posterior fiber bundles. By the tenth dissection, we observed that the nerve could be separated into different numbers of fiber bundles at different levels, and from this point on care was taken to identify all branches of the nerve and then to dissect these branches with micro equipment in a retrograde direction within the epineurium. Thus 23 specimens were studied-20 by successful microdis-
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Fig. 1. After removal of its sheath of brachial fascia, the nerve is still held in place by a fine areolar tissue.
Fig. 2. Mesoneurium in partially dissected specimen.
section, 1 unsatisfactorily because of poor preservation, and 2 by means of serial histologic sections (not reported here). The positions of the branches were measured and recorded with reference to a zero line drawn between the epicondyles of the humerus in 20 specimens. Measurements were rounded off to the nearest 0.5 cm because the dissection of the nerves altered their positions in their beds, making the measurements gross. The number of branches in each specimen, their origins and destinations, and their positions with reference to the interepicondylar line were recorded both before and after microdissection. Sketches were made of each gross dissection and each microdissection, and photographs were taken of most. All branch interconnections, no matter how complicated, were recorded. For the sake of brevity and clarity, the following abbreviations will be used:
that was continuous with the fascia of the brachialis and biceps muscles. The thickness of the fascia varied from specimen to specimen, occasionally being quite heavy approximately 5 cm above the elbow. In some, this sheath extended to the lacertus, but in most it terminated 3 to 5 cm above it, leaving a gap where the nerve was surrounded by areolar tissue. When the fascial sheath was opened, the nerve was still held in place by areolar tissue in which there were tiny bandlike thickenings (Fig. 1). An extensive mesoneurium stretched from the bed of the nerve and connected all of the branches (Fig. 2). A small vessel was found in the mesoneurium, entering the posterior aspect of the nerve 5 cm above the IL in more than half the cases.
IL = Xnterepicondylar line Med N = Median nerve Prt = Pronator teres muscle FCR = Flexor carpi radialis muscle FDS = Flexor digitorum superficialis muscle PL = Palmaris longus muscle FDP = Flexor digitorum profundus muscle FPL = Flexor pollicis longus muscle PrQ = Pronator quadratus muscle AIN = Anterior interosseous nerve Results Gross anatomy of the nerve environment. In the arm, the nerve was contained within a fascial sheath
The nerve left the arm under the lacertus fibrosis, which varied in size and thickness and was not constrictive. Then the nerve passed under the pronator teres muscle or under a thick fibrous band in the ulnar head of the muscle. It then passed under the proximal edge of the flexor digitorum superficialis, which often had a fibrous edge. In four cases, the origin of the pronator teres muscle was 4 cm above the epicondyle. In three of these cases the origin was from the medial intermuscular septum, and in one it was from a ligament of Struthers that ran to the medial epicondyle from a bump on the anteromedial humerus. An abnormality observed with a high pronator origin was a more proximal branching of the nerve to the pronator teres and the anterior interosseous nerve in three of four cases. Gross and microdissection of nerve branches. There appeared to be four nerve branches or groups of
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Fig. 3. Specimen 31. A, Gross dissection of major branching patterns. B, Appearance aches and fiber bundles after microdissection, a complicated pattern in this case. _’
Table I. Sites of branching
in reference
to interepicondylar
line
Gross dissection Average (cm) +1.5
- 1.5 -3.0 -7.0 - 16.5
of nerve
Microdissection Nerve branch
Average (cm)
to +3.0 to +4.0
I II III
+ 10.0 -
to -4.0 to -9.0 to - 14.0
V VI
Range (cm) -3.5 -5.0 -7.0 - 8.0 - 16.0 - 18.0
to +4.5
The numerical averages and ranges for the branching points depicted in Fig. 4. With the interepicondylar proximal and (-) the distance distal to the interepicondylar line.
+4.5 -4.5 - 12.5 - 15.5
Range (cm) +6.0 to + 15.0 -6.0 -7.0 - 15.0 - 17.0
line as a 0 reference point, (+)
to +8.0
to -2.0 to - 10.0 to - 12.5
indicates the distance
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GROSS DISSECTION cm
651
MICRO DISSECTION cm
Fig. 4. Average branching points of the 6 major nerve groups in 20 specimens. A, Gross dissection. B, Microdissection. branches exiting from the median nerve in the region of the elbow (Fig. 3): I II III IV
ZZ = = =
Nerves to the PrT Nerves to FCR, FDS, PL The anterior interosseous nerve Nerves to FDS
Two smaller nerve branches (V to FDS and VI to FDS) arose in the midforearm. They were nearly constant findings, but they were dissected and measured in only six specimens. There was considerable variation as to which branches supplied which muscle, especially in group II, which was rarely a primary branch from the median nerve and was usually made up of contributions from branches I and Ill. Branches lV, V, and VI were very constant. Most of the branches came from the posterior or medial aspect of the median nerve, especially branch III, the AIN. Branches I, II, and III could be followed
Table II. The average lengths that branches can be dissected proximally within the epineurium of the median nerve Nerve branch
Average microdissection distances {cm)
I
10.0*
II III
7.5
IV
2.0
V
1.0
VI
1.0
*The measurement was taken from the average site of the multiple branches to pronator tens, not from the highest one.
for considerable distances within the median nerve without injury. The nerve in the elbow region was a collection within an epineural wrap of these branches that had defined themselves in the nerve more proximally.
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Table III. A summary of the data concerning No. of branches
I Branch group
Origin of branches
2.2*
II
1.2
III
1.1
IV
1.1
-
3
-
2
Destination of jibers
I
Actual
)Average h;T;r;l
I
nerve branches
Gross
Microdissection
Gross
Microdissection
All from median nerve
All from median nerve 1 contribution from III
All 20 to PrT
10 7 -
17 from median nerve 2 from I and II 1 from III
19 to FDS, PL, FCR 1 to AIN (III)
18 2 -
All from median nerve
1 from median nerve 7 from median nerve and I 3 from I 6 from I and III 3 from III 19 from median nerve 1 from median nerve and II
All 20 to PrT 19 to II - 16 FCR - 5 FDS 2 to median nerve t Same
All 20 to AIN 2 to FDS (VI)
1.5 3 -
18 from median nerve 2 from III
All from median nerve
All to FDS
1 6
3
All 20 1 to 4 to 2 to 2 to Same
to AIN I II I and II II and IV
For each nerve group, the number of branches, their origins, and their destinations are listed. The many variations are documented. *Number based on last 10 dissections. tOnce the nerve or nerves were formed. PrT = pronator teres; FCR = flexor carpi radialis; FDS = flexor digitorum superficialis; AIN = anterior interosseous nerve.
The major nerve branches are described, and Fig. 4 and Tables I, II, and III summarize the data. Variations were too numerous to permit sketches of all, but Figs. 5 to 7 represent general patterns along with some variations. Branch I. Branch I was present in all specimens. It was the first branch in 19 of 20 specimens, the exception being in a specimen in which a portion of branch II came off first. Even then, branch I was most proximal after microdissection, a finding common to all 20 specimens . Branch I supplied the PrT in all cases, but in 19 of 20 specimens it also carried fibers to muscles innervated by branch II. The most common of these was the FCR, which appeared to receive a contribution from branch I in 16 of 20 specimens. The most proximal branch of I came off the median nerve at an average of 1.5 cm above the IL (+ 1.5) with a range of + 4.5 to - 3.5 cm. In three of the four specimens in which there was a high origin of the PrT the first pronator branch came off at +4 cm. In nine specimens that had more than one branch to the PrT, the most distal came off the median nerve at an average - 1.5 cm, with a range of 0 to -4 cm. After microdissection, all of the terminal branches to PrT originated in a single trunk, I, and the branching point for this averaged + 10 cm, with a range of + 6 to + 15 cm.
The pronator branches usually left the median nerve from its posterior or medial surface, although in five specimens one branch came off anteriorly but was posterior after microdissection. Four lateral branches were seen and innervated a well-developed ulnar head of the PrT. The bundle of fascicles that contained all the branches of I could be dissected proximally an average of 10 cm (range, 4.0 to 13.5 cm) from the average departure point of the branches of the PrT. In 3 of 20 specimens, branch I was dissected to 9 cm or less above the IL, and these were dissected to + 6, + 8, and + 8.5 cm. In 4 of 20 specimens, the total dissectability of branch I was 8 cm or less, and 3 of these were in cases of high pronator teres origin. Branch I appeared to be the sole contributor to the pronator teres muscle in 19 of 20 specimens. In addition to carrying branches to the FCR in 16 specimens, it appeared to have branches to FDS in five. In two instances, it also returned a branch back to the median nerve. It appeared that the PrT and FCR innervations frequently ran in the same fiber bundles and that these two muscles were coupled in their innervation patterns. Branch II. Branch II was a variable nerve or group of nerves. Ten specimens had one branch, seven had two, and three had none as the fibers to muscles were carried in branch III. Fibers that made up branch II
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SPECIMEN
SPECIMEN
653
#lO
#lO
Fig. 5. Specimen 10. A, Gross dissection. I, II, and IV are single branches, but IV actually came rare finding. Branch II consists of two branches, as it did in seven specimens. B, Microdissection. I, III, and IV branched directly from the median nerve. II was formed from I and III. This simple pattern was seen in six specimens.
off III-a
came from branch I in three instances, from a combination of the median nerve and branch I in seven, from branch III in three, and from a combination of branches I and III in six. In these combinations, the branches to the FCR usually came from branch I, and those to FDS and PL came from branches II and III. In addition to this apparent coupling of innervation between PrT and FCR, there appeared to be a similar relationship between FDS and PL. In one specimen branch II was the most proximal, and this was the only specimen in which a nerve to the pronator was not the highest branch. This was seen on gross dissection, but the nerve came off below the pronator branches after microdissection. Branch group II existed in 17 specimens on gross examination, and the
most proximal branch came off the median nerve at an average of - 1.5 cm (range, + 3 to - 5 cm). Only one nerve originated above the medial epicondyle; most came off posteriorly and medially, but a few were anterior or lateral. In the seven specimens with two branches, the more proximal branches supplied the FDS and PL in six, and the lower branch supplied the FCR. This order was reversed in one specimen. In six of the seven, the two branches were within 1 cm of each other. This branch group supplied the FCR, FDS, and PL in 19 of the 20 specimens. In the remaining one, it supplied the same muscles and gave a branch to III. Branch III. Branch III was a single nerve in 18 specimens and two nerves in two specimens. When
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SPECIMEN #32
SPECIMEN #32
Fig. 6. Specimen 32. A, Two branches represented each of I, II, and IV. In the series, I and II were commonly multiple (see Table I). III was usually single. B, Microdissection. Similar to specimen 10, but IV consisted of two branches, a rarity. Again, II comprises branches I and III.
there were two, one was a small branch just proximal to the AIN and innervated the FDP. Branch III innervated the FPL, FDP, and presumably PrQ, although we did not trace the nerve all the way to PrQ. It came from the posterior aspect of the median nerve in all 20 specimens. With only one exception, it could bem,dissected above the IL, usually to a point + 4 to + 7 cm above the IL. Branch III, on gross dissection, left the median nerve at an average of - 3 cm (range, - 7 to + 4 cm). The nerve came off above the IL only four times and at or below the IL 16 times. After microdissection, the average exit point was +4.5 cm, with a range of + 8 to -6 cm. The one branch that could be dissected to
only - 6 cm was clearly anomalous, since the next lowest recording was + 1.5. The average length that branch III could be dissected from its branching point was 7.5 cm. After microdissection, all 20 group III branches came directly from the median nerve. Sixteen exited alone, while four received small branches from the median nerve (three) or from branch II (one). In 9 of the 20 specimens, microdissection showed that branch III carried with it part or all of other nerves: one to branch I, four to branch II, two to branches I and II, and two to branches II and IV. Branch IV. Group IV had one branch in 15 speci-
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SPECIMEN #23
SPECIMEN #23
Fig. 7. Specimen 23. A, Gross dissection; the second branch to the pronator teres came off with B, Microdissection. II came completely from I, a pattern found in only three specimens.
II.
mens, two branches in three, and none in two. In the two specimens with no branch IV, the nerve ran with branch III but was easily separated by microdissection and was autonomous. Eighteen were separate from branch III by gross dissection. Branch IV left the median nerve -7 cm from the IL (range, - 8 to - 4 cm). It could be dissected only short distances to an average of -4.5 cm (range, -7 to - 2 cm). It could be dissected an average of 2 cm (range, 1 to 4 cm). This nerve always terminated in the FDS, with an occasional branch innervating the PL. General patterns. Certain patterns seemed fairly constant. All pronator teres branches came from a single branch I in every specimen. When branch I contributed
to branch II, it almost always innervated the FCR. When branch III contributed to branch II, it almost always innervated the FDS and the PL. Although FDS and PL (usually IIa) were innervated by a more proximal branch than FCR (usually IIb) on gross dissection, this order was reversed after microdissection in most specimens. Branches V and VI always remained independent and could not be dissected more than 1.5 cm proximally.
Discussion In 1946 Sunderland reported that the fascicular pattern of nerves in the arm was continually modified by plexiform connections and that the average length over which any nerve had a constant pattern was less than
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5 mm. However, he also wrote in the same publication: “Despite the changing plexiform character of the funicular pattern, fibers from peripheral branches pursued a localized course in the nerve for variable, though often considerable, distances.” He was referring specifically to a single specimen of the median nerve in the region of the elbow. Like Sunderland, Jabaley et a1.5 studied a very few specimens of the median nerve by means of serial histologic sections and concluded that some fiber bundles remain intact for long distances within the median nerve before exiting as branches. In a study performed by microdissection, Blair and Joos6 examined the innervation of the FCR only. Their findings differed from ours in that they reported a single nerve to FCR in 19 of 20 specimens whereas we found a single group II nerve in only 10 of 20 specimens. The point of their article was that although the FCR was innervated solely by a branch or branches from the median nerve in all 20 specimens, microdissection demonstrated a contribution from the anterior interosseous nerve (our branch III) in 12. We found that the frequent contribution of branch III (AIN) to branch II (9/20) generally went to FDS and PL, not to FCR. Our data concerning numbers and destination of branches of the median nerve in the region of the elbow are similar to those of Linell’ and Sunderland.2,3 How-
ever, we have demonstrated the distances over which these branches can be identified within the median nerve on proximal dissection and have shown the patterns of branching that remain after intraneural dissection. This information may help in nerve repairs and nerve grafting, as well as in selective denervation for spasticity. Also, it may lead to an understanding of why similar nerve compressions can cause different clinical syndromes. REFERENCES 1. Line11 E. The distribution of nerves in the upper limb, with reference to variabilities and their clinical significance. J Anat London 1921;.55:79-112. 2. Sunderland S, Ray L. Metrical and non-metrical features of the muscular branches of the median nerve. J Comp Neurol 1946;85:191-203. 3. Sunderland S. Nerves and nerve injuries, ed 2. Edinburgh: Churchill-Livingstone, 1978. 4. Sunderland S. The intraneural topography of the radial, median, and ulnar nerves. Brain 1945;68:243-98. 5. Jabaley M, Wallace W, Heckler F. Internal topography of major nerves of the forearm and hand: a current view. J HAND SURG 1980;5:1-18. 6. Blair W, Joos K. The innervation of the flexor carpi radialis: an interfascicular dissection, Arch Neurol 1982; 39:647-9.
Stephen F. Gunther, MD, Doreen DiPasquale, MD, Washington, D.C., LCDR Robert Martin, MC, USN, Bethesda, Md.
T
his study of the internal anatomy of the median nerve in fresh and fresh frozen human cadavers was prompted by two unusual cases of median neuropathy above the elbow. A search of the literature revealed that little has been published on the gross anatomy of median nerve branching near the elbow, and even less on the internal anatomy. Although current texts give general descriptions of branching patterns, one must go back to the works of Linell’ in 1921 and Sunderland and Ray’ in 1946 for accurate and detailed descriptions. Sunderland is credited with demonstrating that axons travel from one fascicle to another along the course of
From the Departments of Orthopaedic Surgery of the Washington Hospital Center and George Washington University, Washington, D.C., and the Anatomical Teaching Laboratory of the Uniformed Services University of Health Sciences, Bethesda, Md. This work was presented at the annual meeting of the American Society for Surgery of the Hand in Seattle, Wash., Sept. 24, 1990. It was awarded the Emmanuel B. Kaplan Prize by the New York Hand Society. Received for publication July 17, 1991.
May 24, 1990; accepted
in revised form
No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Reprint requests: Stephen F. Gunther, MD, Washington Hospital Center, Department of Orthopaedic Surgery, 110 Irving St., NW, Washington, DC 20010. 311132566
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and
a nerve, and he also pointed out that this interchange may cease near large joints, where fascicles sometimes remain autonomous for certain distances before separating off to form branches. Only Sunderland3.4 and Jabaley et al.’ have reported studies of the internal topography of the median nerve in the region of the elbow. Between them, they have reported fewer than five specimens. The specimens were studied principally by means of serial histologic sections, which in Jabaley’s study did not go above the elbow. Although helpful and stimulating, these few reports did not completely answer our questions as to how similar nerve lesions above the elbow could cause different clinical syndromes. Therefore the median nerve was studied above and below the elbow by gross and microdissection techniques in fresh cadavers. Material and methods Thirty-two unpreserved cadaver arms, mostly fresh frozen and thawed, were used in this study. The first nine dissections studied the surroundings of the median nerve and its arrangement into anterior and posterior fiber bundles. By the tenth dissection, we observed that the nerve could be separated into different numbers of fiber bundles at different levels, and from this point on care was taken to identify all branches of the nerve and then to dissect these branches with micro equipment in a retrograde direction within the epineurium. Thus 23 specimens were studied-20 by successful microdis-
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649
Fig. 1. After removal of its sheath of brachial fascia, the nerve is still held in place by a fine areolar tissue.
Fig. 2. Mesoneurium in partially dissected specimen.
section, 1 unsatisfactorily because of poor preservation, and 2 by means of serial histologic sections (not reported here). The positions of the branches were measured and recorded with reference to a zero line drawn between the epicondyles of the humerus in 20 specimens. Measurements were rounded off to the nearest 0.5 cm because the dissection of the nerves altered their positions in their beds, making the measurements gross. The number of branches in each specimen, their origins and destinations, and their positions with reference to the interepicondylar line were recorded both before and after microdissection. Sketches were made of each gross dissection and each microdissection, and photographs were taken of most. All branch interconnections, no matter how complicated, were recorded. For the sake of brevity and clarity, the following abbreviations will be used:
that was continuous with the fascia of the brachialis and biceps muscles. The thickness of the fascia varied from specimen to specimen, occasionally being quite heavy approximately 5 cm above the elbow. In some, this sheath extended to the lacertus, but in most it terminated 3 to 5 cm above it, leaving a gap where the nerve was surrounded by areolar tissue. When the fascial sheath was opened, the nerve was still held in place by areolar tissue in which there were tiny bandlike thickenings (Fig. 1). An extensive mesoneurium stretched from the bed of the nerve and connected all of the branches (Fig. 2). A small vessel was found in the mesoneurium, entering the posterior aspect of the nerve 5 cm above the IL in more than half the cases.
IL = Xnterepicondylar line Med N = Median nerve Prt = Pronator teres muscle FCR = Flexor carpi radialis muscle FDS = Flexor digitorum superficialis muscle PL = Palmaris longus muscle FDP = Flexor digitorum profundus muscle FPL = Flexor pollicis longus muscle PrQ = Pronator quadratus muscle AIN = Anterior interosseous nerve Results Gross anatomy of the nerve environment. In the arm, the nerve was contained within a fascial sheath
The nerve left the arm under the lacertus fibrosis, which varied in size and thickness and was not constrictive. Then the nerve passed under the pronator teres muscle or under a thick fibrous band in the ulnar head of the muscle. It then passed under the proximal edge of the flexor digitorum superficialis, which often had a fibrous edge. In four cases, the origin of the pronator teres muscle was 4 cm above the epicondyle. In three of these cases the origin was from the medial intermuscular septum, and in one it was from a ligament of Struthers that ran to the medial epicondyle from a bump on the anteromedial humerus. An abnormality observed with a high pronator origin was a more proximal branching of the nerve to the pronator teres and the anterior interosseous nerve in three of four cases. Gross and microdissection of nerve branches. There appeared to be four nerve branches or groups of
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Fig. 3. Specimen 31. A, Gross dissection of major branching patterns. B, Appearance aches and fiber bundles after microdissection, a complicated pattern in this case. _’
Table I. Sites of branching
in reference
to interepicondylar
line
Gross dissection Average (cm) +1.5
- 1.5 -3.0 -7.0 - 16.5
of nerve
Microdissection Nerve branch
Average (cm)
to +3.0 to +4.0
I II III
+ 10.0 -
to -4.0 to -9.0 to - 14.0
V VI
Range (cm) -3.5 -5.0 -7.0 - 8.0 - 16.0 - 18.0
to +4.5
The numerical averages and ranges for the branching points depicted in Fig. 4. With the interepicondylar proximal and (-) the distance distal to the interepicondylar line.
+4.5 -4.5 - 12.5 - 15.5
Range (cm) +6.0 to + 15.0 -6.0 -7.0 - 15.0 - 17.0
line as a 0 reference point, (+)
to +8.0
to -2.0 to - 10.0 to - 12.5
indicates the distance
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Internal anatomy of median nerve in elbow region
GROSS DISSECTION cm
651
MICRO DISSECTION cm
Fig. 4. Average branching points of the 6 major nerve groups in 20 specimens. A, Gross dissection. B, Microdissection. branches exiting from the median nerve in the region of the elbow (Fig. 3): I II III IV
ZZ = = =
Nerves to the PrT Nerves to FCR, FDS, PL The anterior interosseous nerve Nerves to FDS
Two smaller nerve branches (V to FDS and VI to FDS) arose in the midforearm. They were nearly constant findings, but they were dissected and measured in only six specimens. There was considerable variation as to which branches supplied which muscle, especially in group II, which was rarely a primary branch from the median nerve and was usually made up of contributions from branches I and Ill. Branches lV, V, and VI were very constant. Most of the branches came from the posterior or medial aspect of the median nerve, especially branch III, the AIN. Branches I, II, and III could be followed
Table II. The average lengths that branches can be dissected proximally within the epineurium of the median nerve Nerve branch
Average microdissection distances {cm)
I
10.0*
II III
7.5
IV
2.0
V
1.0
VI
1.0
*The measurement was taken from the average site of the multiple branches to pronator tens, not from the highest one.
for considerable distances within the median nerve without injury. The nerve in the elbow region was a collection within an epineural wrap of these branches that had defined themselves in the nerve more proximally.
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Table III. A summary of the data concerning No. of branches
I Branch group
Origin of branches
2.2*
II
1.2
III
1.1
IV
1.1
-
3
-
2
Destination of jibers
I
Actual
)Average h;T;r;l
I
nerve branches
Gross
Microdissection
Gross
Microdissection
All from median nerve
All from median nerve 1 contribution from III
All 20 to PrT
10 7 -
17 from median nerve 2 from I and II 1 from III
19 to FDS, PL, FCR 1 to AIN (III)
18 2 -
All from median nerve
1 from median nerve 7 from median nerve and I 3 from I 6 from I and III 3 from III 19 from median nerve 1 from median nerve and II
All 20 to PrT 19 to II - 16 FCR - 5 FDS 2 to median nerve t Same
All 20 to AIN 2 to FDS (VI)
1.5 3 -
18 from median nerve 2 from III
All from median nerve
All to FDS
1 6
3
All 20 1 to 4 to 2 to 2 to Same
to AIN I II I and II II and IV
For each nerve group, the number of branches, their origins, and their destinations are listed. The many variations are documented. *Number based on last 10 dissections. tOnce the nerve or nerves were formed. PrT = pronator teres; FCR = flexor carpi radialis; FDS = flexor digitorum superficialis; AIN = anterior interosseous nerve.
The major nerve branches are described, and Fig. 4 and Tables I, II, and III summarize the data. Variations were too numerous to permit sketches of all, but Figs. 5 to 7 represent general patterns along with some variations. Branch I. Branch I was present in all specimens. It was the first branch in 19 of 20 specimens, the exception being in a specimen in which a portion of branch II came off first. Even then, branch I was most proximal after microdissection, a finding common to all 20 specimens . Branch I supplied the PrT in all cases, but in 19 of 20 specimens it also carried fibers to muscles innervated by branch II. The most common of these was the FCR, which appeared to receive a contribution from branch I in 16 of 20 specimens. The most proximal branch of I came off the median nerve at an average of 1.5 cm above the IL (+ 1.5) with a range of + 4.5 to - 3.5 cm. In three of the four specimens in which there was a high origin of the PrT the first pronator branch came off at +4 cm. In nine specimens that had more than one branch to the PrT, the most distal came off the median nerve at an average - 1.5 cm, with a range of 0 to -4 cm. After microdissection, all of the terminal branches to PrT originated in a single trunk, I, and the branching point for this averaged + 10 cm, with a range of + 6 to + 15 cm.
The pronator branches usually left the median nerve from its posterior or medial surface, although in five specimens one branch came off anteriorly but was posterior after microdissection. Four lateral branches were seen and innervated a well-developed ulnar head of the PrT. The bundle of fascicles that contained all the branches of I could be dissected proximally an average of 10 cm (range, 4.0 to 13.5 cm) from the average departure point of the branches of the PrT. In 3 of 20 specimens, branch I was dissected to 9 cm or less above the IL, and these were dissected to + 6, + 8, and + 8.5 cm. In 4 of 20 specimens, the total dissectability of branch I was 8 cm or less, and 3 of these were in cases of high pronator teres origin. Branch I appeared to be the sole contributor to the pronator teres muscle in 19 of 20 specimens. In addition to carrying branches to the FCR in 16 specimens, it appeared to have branches to FDS in five. In two instances, it also returned a branch back to the median nerve. It appeared that the PrT and FCR innervations frequently ran in the same fiber bundles and that these two muscles were coupled in their innervation patterns. Branch II. Branch II was a variable nerve or group of nerves. Ten specimens had one branch, seven had two, and three had none as the fibers to muscles were carried in branch III. Fibers that made up branch II
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Fig. 5. Specimen 10. A, Gross dissection. I, II, and IV are single branches, but IV actually came rare finding. Branch II consists of two branches, as it did in seven specimens. B, Microdissection. I, III, and IV branched directly from the median nerve. II was formed from I and III. This simple pattern was seen in six specimens.
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came from branch I in three instances, from a combination of the median nerve and branch I in seven, from branch III in three, and from a combination of branches I and III in six. In these combinations, the branches to the FCR usually came from branch I, and those to FDS and PL came from branches II and III. In addition to this apparent coupling of innervation between PrT and FCR, there appeared to be a similar relationship between FDS and PL. In one specimen branch II was the most proximal, and this was the only specimen in which a nerve to the pronator was not the highest branch. This was seen on gross dissection, but the nerve came off below the pronator branches after microdissection. Branch group II existed in 17 specimens on gross examination, and the
most proximal branch came off the median nerve at an average of - 1.5 cm (range, + 3 to - 5 cm). Only one nerve originated above the medial epicondyle; most came off posteriorly and medially, but a few were anterior or lateral. In the seven specimens with two branches, the more proximal branches supplied the FDS and PL in six, and the lower branch supplied the FCR. This order was reversed in one specimen. In six of the seven, the two branches were within 1 cm of each other. This branch group supplied the FCR, FDS, and PL in 19 of the 20 specimens. In the remaining one, it supplied the same muscles and gave a branch to III. Branch III. Branch III was a single nerve in 18 specimens and two nerves in two specimens. When
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Fig. 6. Specimen 32. A, Two branches represented each of I, II, and IV. In the series, I and II were commonly multiple (see Table I). III was usually single. B, Microdissection. Similar to specimen 10, but IV consisted of two branches, a rarity. Again, II comprises branches I and III.
there were two, one was a small branch just proximal to the AIN and innervated the FDP. Branch III innervated the FPL, FDP, and presumably PrQ, although we did not trace the nerve all the way to PrQ. It came from the posterior aspect of the median nerve in all 20 specimens. With only one exception, it could bem,dissected above the IL, usually to a point + 4 to + 7 cm above the IL. Branch III, on gross dissection, left the median nerve at an average of - 3 cm (range, - 7 to + 4 cm). The nerve came off above the IL only four times and at or below the IL 16 times. After microdissection, the average exit point was +4.5 cm, with a range of + 8 to -6 cm. The one branch that could be dissected to
only - 6 cm was clearly anomalous, since the next lowest recording was + 1.5. The average length that branch III could be dissected from its branching point was 7.5 cm. After microdissection, all 20 group III branches came directly from the median nerve. Sixteen exited alone, while four received small branches from the median nerve (three) or from branch II (one). In 9 of the 20 specimens, microdissection showed that branch III carried with it part or all of other nerves: one to branch I, four to branch II, two to branches I and II, and two to branches II and IV. Branch IV. Group IV had one branch in 15 speci-
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Fig. 7. Specimen 23. A, Gross dissection; the second branch to the pronator teres came off with B, Microdissection. II came completely from I, a pattern found in only three specimens.
II.
mens, two branches in three, and none in two. In the two specimens with no branch IV, the nerve ran with branch III but was easily separated by microdissection and was autonomous. Eighteen were separate from branch III by gross dissection. Branch IV left the median nerve -7 cm from the IL (range, - 8 to - 4 cm). It could be dissected only short distances to an average of -4.5 cm (range, -7 to - 2 cm). It could be dissected an average of 2 cm (range, 1 to 4 cm). This nerve always terminated in the FDS, with an occasional branch innervating the PL. General patterns. Certain patterns seemed fairly constant. All pronator teres branches came from a single branch I in every specimen. When branch I contributed
to branch II, it almost always innervated the FCR. When branch III contributed to branch II, it almost always innervated the FDS and the PL. Although FDS and PL (usually IIa) were innervated by a more proximal branch than FCR (usually IIb) on gross dissection, this order was reversed after microdissection in most specimens. Branches V and VI always remained independent and could not be dissected more than 1.5 cm proximally.
Discussion In 1946 Sunderland reported that the fascicular pattern of nerves in the arm was continually modified by plexiform connections and that the average length over which any nerve had a constant pattern was less than
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5 mm. However, he also wrote in the same publication: “Despite the changing plexiform character of the funicular pattern, fibers from peripheral branches pursued a localized course in the nerve for variable, though often considerable, distances.” He was referring specifically to a single specimen of the median nerve in the region of the elbow. Like Sunderland, Jabaley et a1.5 studied a very few specimens of the median nerve by means of serial histologic sections and concluded that some fiber bundles remain intact for long distances within the median nerve before exiting as branches. In a study performed by microdissection, Blair and Joos6 examined the innervation of the FCR only. Their findings differed from ours in that they reported a single nerve to FCR in 19 of 20 specimens whereas we found a single group II nerve in only 10 of 20 specimens. The point of their article was that although the FCR was innervated solely by a branch or branches from the median nerve in all 20 specimens, microdissection demonstrated a contribution from the anterior interosseous nerve (our branch III) in 12. We found that the frequent contribution of branch III (AIN) to branch II (9/20) generally went to FDS and PL, not to FCR. Our data concerning numbers and destination of branches of the median nerve in the region of the elbow are similar to those of Linell’ and Sunderland.2,3 How-
ever, we have demonstrated the distances over which these branches can be identified within the median nerve on proximal dissection and have shown the patterns of branching that remain after intraneural dissection. This information may help in nerve repairs and nerve grafting, as well as in selective denervation for spasticity. Also, it may lead to an understanding of why similar nerve compressions can cause different clinical syndromes. REFERENCES 1. Line11 E. The distribution of nerves in the upper limb, with reference to variabilities and their clinical significance. J Anat London 1921;.55:79-112. 2. Sunderland S, Ray L. Metrical and non-metrical features of the muscular branches of the median nerve. J Comp Neurol 1946;85:191-203. 3. Sunderland S. Nerves and nerve injuries, ed 2. Edinburgh: Churchill-Livingstone, 1978. 4. Sunderland S. The intraneural topography of the radial, median, and ulnar nerves. Brain 1945;68:243-98. 5. Jabaley M, Wallace W, Heckler F. Internal topography of major nerves of the forearm and hand: a current view. J HAND SURG 1980;5:1-18. 6. Blair W, Joos K. The innervation of the flexor carpi radialis: an interfascicular dissection, Arch Neurol 1982; 39:647-9.
