Anatomic variations of the median nerve in the carpal tunnel: a brief review of the literature.

Abstract

Carpal tunnel syndrome (CTS) is a common focal peripheral neuropathy. Increased pressure in the carpal tunnel results in median nerve compression and impaired nerve perfusion, leading to discomfort and paresthesia in the affected hand. Surgical division of the transverse carpal ligament is preferred in severe cases of CTS and should be considered when conservative measures fail. A through knowledge of the normal and variant anatomy of the median nerve in the wrist is fundamental in avoiding complications during carpal tunnel release. This paper aims to briefly review the anatomic variations of the median nerve in the carpal tunnel and its implications in carpal tunnel surgery.

Full text

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Review
Turkish Neurosurgery 2011, Vol: 21, No: 3, 1-9
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ABSTRACT
Carpal tunnel syndrome (CTS) is a common focal peripheral neuropathy. Increased pressure in the carpal tunnel results in median nerve
compression and impaired nerve perfusion, leading to discomfort and paresthesia in the affected hand. Surgical division of the transverse
carpal ligament is preferred in severe cases of CTS and should be considered when conservative measures fail. A through knowledge of the
normal and variant anatomy of the median nerve in the wrist is fundamental in avoiding complications during carpal tunnel release. This paper
aims to briefly review the anatomic variations of the median nerve in the carpal tunnel and its implications in carpal tunnel surgery.
KeywoRds: Median nerve, Anatomic variation, Carpal tunnel, Transverse carpal ligament
ÖZ
Karpal tünel sendromu (KTS) sık görülen bir periferik nöropatidir. Karpal tünel basıncının artması median sinirin sıkışmasına ve kanlanmasının
bozulmasına yol açar. Ağır vakalarda ve konservatif tedavinin yeterli olmadığı durumlarda cerrahi olarak transvers karpal ligamanın kesilmesi
tercih edilir. Karpal tünelin gevşetilmesi sırasında komplikasyonlardan kaçınmak için median sinirin bu bölgedeki ayrıntılı anatomisinin ve
varyasyonlarının iyi bilinmesi gereklidir. Bu derleme median sinirin karpal tüneldeki olası anatomik varyasyonlarını ve bunun karpal tünel
cerrahisine etkilerini kısaca gözden geçirmek amacıyla yazılmıştır.
ANAHTAR sÖZCÜKLeR: Median sinir, Anatomik varyasyon, Karpal tünel, Transvers karpal ligaman
Correspondence address: Emre DEmIrCay / E-mail: emredemircay@hotmail.com
Emre DEmIrcay1, Erdinc cIvElEk2, Tufan cansEvEr2, serdar kabaTas2, cem yIlmaz3
1Baskent University, Faculty of Medicine, Department of Othopedics and Traumatology, Istanbul, Turkey
2Baskent University, Faculty of Medicine, Department of Neurosurgery, Istanbul, Turkey
3Baskent University, Faculty of Medicine, Department of Neurosurgery, Ankara, Turkey
anatomic Variations of the median Nerve in the
Carpal Tunnel: a Brief review of the Literature
Median Sinirin Karpal Tüneldeki Anatomik Varyasyonları:
Literatürün Kısa Bir Derlemesi
received: 16.03.2010 / accepted: 27.03.2011
InTRoduCTIon
Entrapment of the median nerve in the carpal tunnel is one
of the most common entrapment neuropathy syndromes
in clinical practice (3,20). The main causes of this syndrome
include repetitive strain, wrist fracture, rheumatoid arthritis, a
space-occupying lesion, dialysis-related amyloidosis, diabetes
mellitus, and cases with no apparent cause (27,33). Phalen GS
found thickening of the synovium in most of the operative
cases and concluded that thickening or fibrosis was the most
common cause of the syndrome (29).
Anatomic variations of the median nerve are frequent and
they are significant for wrist surgery particularly in the
treatment of CTS. Surgical techniques with short incisions
and endoscopic procedures demand a thorough knowledge
of the anatomy and variations of the structures in the wrist.
Surgical anatomy of carpal tunnel
The flexor retinaculum and carpal tunnel: The flexor
retinaculum is a strong ligament that forms the roof of the
transverse carpal arch. Its main function is to serve as a flexor
pulley at the wrist for the flexor tendons. It is attached to
the pisiform, hamate, scaphoid, and trapezium, converting
the palmar arch into the carpal tunnel. The carpal tunnel is a
narrow fibro-osseous tunnel through which the median nerve
passes with nine tendons (four flexor digitorum superficialis,
four flexor digitorum profundus and flexor pollicis longus) and
sometimes accompanied by persistent median artery (Figure
1). Carpal tunnel behaves like a closed compartment and
maintains its own tissue fluid pressure levels (35). Anomalous
elongation of the muscle bellies of the flexor digitorum
superficialis, the palmaris longus, patent median artery, or
a proximal origin of a lumbrical muscle may compress the
contents of the carpal tunnel. The proximal wrist flexion
crease identifies the proximal edge of the carpal tunnel and
it ends at the base of the third metacarpal. Proximal portion
of the flexor retinaculum is a direct continuation of the deep
antebrachial fascia. The transverse carpal ligament represents
the central portion of the flexor retinaculum. Distally is an
aponeurosis between thenar and hypothenar muscles (7).
(Figure 2).

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Demircay E, et al: Anatomic Variations of the Median Nerve
Carpal tunnel width at the hook of hamate is narrowest,
at the level of the hook of hamate with a mean of 20mm,
approximately 2 – 2.5 cm distal to its most proximal margin.
It is the thickest portion of the transverse carpal ligament. It
expands to a mean width of 24 – 25mm at its proximal and
distal margins (7). This has been questioned through more
recent studies. It was reported that neither the width, nor
depth, nor cross-sectional area changes significantly along
the length of the carpal tunnel (6,28). The definitions of
proximal and distal extends of the carpal tunnel might be
responsible for this argument since the reported length of the
carpal tunnel is 12.7 ± 2.5mm in one study and 21.7 ± 6.05 in
the other (7,28).
The median nerve: The median nerve is a mixed motor
and sensory nerve; it is composed of branches from C5
through T1 spinal cord nerve roots. The sensory distribution
is from radial three and half digits and part of the thenar
eminence. The motor supply is to the radial two lumbricals
and the muscles of the thenar eminence. The median nerve
descends beneath the flexor digitorum superficialis, lying
on the flexor digitorum profundus in the forearm, within 5
cm of the transverse carpal ligament, and then it becomes
more superficial, situated between the tendons of the flexor
digitorum superficialis and flexor carpi radialis (13). It lies
behind and radial to the side of the palmaris longus tendon
just before entering into the carpal tunnel. Approximately 5
cm proximal to the wrist crease, palmar cutaneous branch
of the median nerve originates from the anterolateral or
volar-radial quadrant of the median nerve under the radial
margin of the flexor digitorum superficialis. It parallels the
median nerve for a distance of 16 – 25 mm, and then courses
separately attaching itself to the antebrachial fascia under the
ulnar border of the flexor carpi radialis tendon. Flexor carpi
radialis enters its tunnel between the superficial and deep
layers of the transverse carpal ligament while the palmar
cutaneous nerve enters very short tunnel of its own, only nine
millimeters long within the ligament, immediately medial to
the tunnel of the flexor carpi radialis tendon (6,38).
The median nerve is located between the flexor retianculum
and the tendons of the middle finger flexor digitorum
superficialis muscle in wrist extension (sublimis 2) (45).
Flexion produces an anterior shift of the tendons toward
the flexor retinaculum. The median nerve either becomes
flattened against the flexor retianculum anterior to sublimis
2 or becomes interposed between individual flexor tendons,
most commonly sublimis 2 and the flexor pollicis longus, but
also sublimis tendons 3 and 4. The flexed position places the
median nerve, flexor tendons, and flexor retinaculum in closer
proximity to each other. This anatomic crowding is consistent
with the proposition that wrist flexion rather than extension
as a predisposing mechanism to carpal tunnel syndrome,
despite carpal tunnel pressure increases with both (12, 39).
The median nerve normally divides into six branches at the
distal terminus of the flexor retinaculum. The six branches
include the recurrent motor branch that innervates the
Figure 1: Axial section of the carpal tunnel through distal carpal
row. FdS I – IV: flexor digitorum superficialis I to IV; FPL: flexor
pollicis longus tendon; a: artery; n: nerve; FCR: flexor carpi
radialis tendon; FdP I – IV: flexor digitorum profundus I to IV; H:
hamate; C: capitate; Td: trapezoid; Tm: trapezium. Flexor carpi
radialis tendon is in a separate compartment.
Figure 2: The flexor retinaculum and carpal tunnel. Proximal
entrance into the carpal tunnel is shown between the tendons of
flexor carpi ulnaris (FCu) and flexor carpi radialis (FCR), contents
of the carpal tunnel are not shown (**). The thickest portion of
the carpal ligament is at the level of hook of hamate (*), it ends at
the level of carpometacarpal joints as a thinner structure.

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Demircay E, et al: Anatomic Variations of the Median Nerve
abductor pollicis brevis, flexor pollicis brevis, opponens
pollicis before dividing into its terminal sensory branches.
There are proper digital nerves to the radial and ulnar sides
of the thumb, and radial side of the index finger. These may
emerge from the median nerve as a common digital nerve.
The point of origin of the thenar branch is on the midpoint of a
line drawn between the tubercle of the scaphoid and the distal
end of the flexion crease of the thumb metacarpophalangeal
joint (32). The penetration of the recurrent motor branch into
the thenar musculature lies at the intersection of the cardinal
line and the proximal continuation of the radial border of the
long finger (11). Finally two common digital nerves branch
to the second and third web spaces (44). The first lumbrical
muscle is innervated by motor branches that originate
from the radial proper digital nerve to the index finger; the
second lubrical muscle is innervated by motor branches that
originate from the second common digital nerve (13). Distal
branches of the median nerve, especially the third common
digital nerve (TCDN) is at risk during an open or endoscopic
carpal tunnel release (9,11,13).
A line drawn from the scaphoid to the radial cleft of the ring
finger intersects the thenar flexion crease at about the location
of the recurrent motor branch of the median nerve within the
carpal canal; by flexing the long finger down adjacent to the
ring finger, the tip of the long finger will touches the site in
the thenar musculature where the thenar nerve arborizes.
Since the origin of the recurrent motor branch within the
carpal canal is along the thenar flexion crease, and incision to
expose carpal canal or to incise the carpal transverse ligament
should be ulnar to that crease and to the underlying ligament
(16).
The distal edge of the carpal tunnel
The superficial palmar arch, a branch of the ulnar artery,
along with the deep palmar arch, a branch of the radial
artery supply blood to all fingers of the hand. The superficial
palmar arch was reported to be 18.8 ± 0.6 mm distal to the
intersection of the distal transverse carpal ligament and the
longitudinal line from the third web space (31). Injury to the
superficial palmar arch can be avoided with knowledge of its
location during open, limited incision or endoscopic carpal
tunnel release. A communicating branch between the ulnar
and median sensory nerves is described. This branch usually
crosses the metacarpal space distal to the superficial palmar
arch, but in some cases it may cross further proximally, just
distal to the edge of the transverse carpal ligament. This
position makes it vulnerable to injury during carpal tunnel
release (24). The hook of the hamate marks the ulnar edge of
the flexor retinaculum. The deep motor branch of the ulnar
nerve passes next to the ulnar side of the hook of the hamate.
If the ulnar side of the flexor retinaculum is divided in an
attempt to avoid the median nerve, the motor branch of the
ulnar nerve may be injured. If distal retinaculum is divided in
a radial direction care must be taken with the third common
digital nerve (11).
dISCuSSIon
Varying results have been reported on the prevalence of
median nerve anomalies. Median nerve variations are well
described due to its diagnostic and surgical importance
(1,9,10,21). Lanz classified the variations of the course of the
median nerve into four groups: Group O: Extraligamantous
thenar branch (standard anatomy), Group I: Variations in the
course of the thenar branch, Group II: Accessory branches of
the median nerve at the distal portion of the carpal tunnel,
Group III: High divisions of the median nerve, Group IV:
Accessory branches proximal to the carpal tunnel (21). Group
I is divided into four subgroups. Group I a, the motor branch
of the median nerve starts beneath the transverse ligament
and then bends around its distal edge (subligamentous). In
Group I b, the motor branch originates from the radial side
of the median nerve and then passes through the transverse
ligament (transligamentous). In Group I c, the motor branch
arises from the ulnar side of the median nerve. In Group I d, the
motor branch bends around the distal edge of the ligament
(supraligamentous) (Figure 3). The transligamentous course
is of great clinical significance because of the possibility of
compression within the retinacular fibers (16).
It was concluded that the recurrent motor branch found to be
originating from extreme radial aspect of the median nerve
in 60% of the dissections, in 22% from the central anterior
aspect, and between the extreme radial – anterior and the
central aspect of the median nerve in the remaining 18% (44).
Hurwitz et al. reported an anomalous origin of the recurrent
motor branch in 21% of 80 hands. He observed multiple motor
branches in 12.5% of the hands. He draw attention to an
additional anomaly in seven patients (9%); the motor branch
arose from the anterior surface of the median nerve, turning
ulnar and crossing the distal edge of the flexor retinaculum
under the cover of a hypertrophic abductor pollicis brevis
muscle. The nerve can easily be injured during splitting of the
flexor retinaculum with this anomaly (14). The nerve should
be approached from ulnar side to minimize risk of lesion. In a
study, it was founded that the recurrent motor branch of the
median nerve passes through a separate tunnel immediately
prior to entering the thenar muscles in 56% of the dissections
(23).
Group II is characterized by the true duplications of the
thenar branch and additional thin sensory branches, which
originates from the palmar or ulnar side of the median nerve.
Falconer and Spinner noted duplication of the recurrent
motor nerve in two of ten specimens examined, in which
a transligamantous branch supplied the abductor pollicis
brevis and the opponens, and in separate extraligamantous
branches supplying the superficial flexor pollicis brevis (10).
Individual variations such as an accessory branch distal to the
carpal tunnel (Lanz group II) with the third common digital
nerve (terminal branches) originating proximal to the distal
edge of the TCL have also been reported (8).
Group III may be further divided in to three subgroups
according to the absence (Group III a) or the presence of a

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Demircay E, et al: Anatomic Variations of the Median Nerve
perforates the retinaculum passing through its own tunnel
(transligamantous) to the thenar musculature (21). Accessory
branches of the median nerve in the distal portion of the
carpal tunnel (group II) were found in 18 hands (7%), high
division of the median nerve (group III) in 7 hands (3%), and
4 hands (1.6%) had accessory branches proximal to the carpal
tunnel (group IV) (21). On the other hand, Lindley and Kleinert
observed 1% (5 hands) with median nerve or its palmar
cutaneous branch or motor branch anomalies during the
course of 526 elective carpal tunnel releases in one surgeon’s
practice (22). Furthermore, Tountas CP et al. reported on 821
median nerves undergoing surgery to treat CTS. Ninety-two
cadaver median nerves were also dissected to document the
incidence of variations within the carpal canal. The combined
incidence of anomalies at operation (Lanz groups I to IV) was
9.8% and 18% in the cadaver series. Their 1.42% of cases fit
into Lanz group I, whereas Poisel reported 54%. The difference
median artery (Group III b) or an accessory lumbrical muscle
(Group III c) between the two branches of the proximally
divided median nerve. A high division of median nerve in
which the radial branch passing through its own compartment
of the carpal tunnel was described by Amadio (2).
There are accessory branches leaving median nerve proximal
to the carpal tunnel in Group IV. Accessory thenar branch may
run directly in the thenar muscles (Group IV a), or it may join
another motor branch first (Group IV b).
Lanz at al. reported 12% (29 hands) variations in the course
of the median nerve in 246 hands. The motor nerve branches
from the median nerve distal to the end of the flexor
retinaculum (extraligamantous), doubled back to innervate
the thenar eminance in 46% of cases, and branches from the
median nerve under the flexor retinaculum (subligamantous)
in 31% of the cases, in 23% of cases, the motor branch
Figure 3: Lanz classification of the median nerve anatomical variations at the wrist. Group I, Thenar branch variations; 1A:
subligamentous; 1B: transligamentous; 1C: ulnarwards; 1d: supraligamentous. Group 0, extraligamentous thenar branch. Group II,
distal accessory thenar branch. Group IV, proximal accessory thenar branch; 4A: running directly in the thenar muscles; 4B: joining
another branch. Group III, high division of the median nerve; 3A: without an artery of muscle; 3B: with artery; 3C: with lumbrical
muscle.

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a similar route to that in Lanz Group IV (36). Kozin dissected
101 fresh frozen cadavers, in 7% of the cases recurrent branch
of the median nerve passed through the transverse carpal
ligament, in 74% of the cases recurrent nerve passed distal
to the TCL through separate obliquely oriented fascia and in
19% of the cases it passed distal to the TCL but did not pass
through the obliquely oriented fascia. He concluded that the
transligamentous branch is uncommon and the reported
high incidance of branches passing through the TCL can be
explained by mistakenly combining recurrent nerves passing
through the obliquely oriented fascia with the recurrent
nerves passing through TCL (19).
An accessory branch of the recurrent nerve was identified, in
31.6% of the 60 cadaver hands (1). It had proximal origin in
13.6% of cases, distal origin in 13.6%, and both proximal and
distal origins in 5.1% of the cases (1). Additionally, Steinberg
et al. dissected 46 hands and in 10 hands they found an
accessory branch of the median nerve piercing the lateral
carpal ligament 3 to 6 mm distal to the proximal edge of the
tunnel. The branch was approximately 1 mm wide, leaving the
radial or volar side of the median nerve at a right angle. They
considered it as a sensory branch due to its size and course
(36).
High bifurcation of the median nerve in the forearm has been
reported by several authors. If care is not taken to do TCL
division under direct vision it is possible to cut the ulnar part
of the divided median nerve (17,21,43).
Median nerve variations reported in the literature are
summarized in Table I.
The position and course of the median nerve within the carpal
tunnel also shows some variations (Figure 4).
a. The nerve passes dorsal to the flexor retinaculum to the
palm without curving in two thirds of the cases.
i. The median nerve is shifted to the radial side of the
carpal tunnel in 43.3%
ii. Below the middle of the flexor retinaculum in 21.7%
iii. It is shifted to the ulnar side in 1.7%.
b. Median nerve curves within the carpal tunnel.
i. Diverging to the radial in 21.6% of the cases.
ii. Diverging to the ulnar side in 11.7% of the cases (32)
Anatomic variations for the origin of the third common
digital nerve were grouped into three specific types: Type I
originating proximal to the distal edge of the transverse carpal
ligament (TCL) (15%), type II originating distal to the TCL but
proximal to the superficial palmar arch (70%), and type III
originating distal to the TCL and at or distal to the superficial
palmar arch (15%). Type I variation is especially at risk for it
originates in the carpal tunnel, but an oblique course of all
variations to the TCDN makes them all susceptible to injury
due to the longitudinal direction of the incision to divide the
TCL (9,17). Open carpal tunnel release has the benefit of direct
visualization of the median nerve and its branches. Although
could not be explained and they concluded further studies
were needed (41).
Stancic et al. reported that 48 hands showed standard
anatomy in exploration of 100 hands. Seventeen hands were
in Lanz Group 1A, 16 hands were in Lanz Group 1B, 5 hands
were in Lanz Group 1C, 2 hands were in Lanz Group 1D, 7
hands were in Lanz Group 2, 1 hand was in Lanz Group 3B,
and 4 hands were in Lanz Group 4A (34).
Olave et al. reported that normal anatomy of the recurrent
branch of the median nerve was observed 48.3% of 60 cases,
18.3% of the cases were in Lanz Group 1A, 15% in Lanz Group
1B, 16.7% of the cases in Lanz Group 1C, an accessory thenar
branch was found in 23 cases, 38.3% of the total cases (Lanz
Group II) (26).
In a series of 110 patients who underwent open carpal surgery,
Beris et al. reported variations of median nerve at the wrist
in 11 patients (10%). 3 cases were in Lanz Group 1A (2.7%), 2
were in Lanz Group 1C (1.8%), 3 in Lanz Group 2 (2.7%), and
2 cases in Group 3B (1.8%). Palmar cutaneous branch of the
median nerve was seperated from the radial aspect of the
nerve few milimeters distal to the proximal border of the
transverse carpal ligament in one patient. This variation poses
a special risk of iatrogenic injury during either endoscopic or
open carpal tunnel release (4).
Falconer et al. evaluated anatomic variations in the motor
and sensory supply of the thumb in ten preserved cadaver
forearms.The motor branch divided distal to the distal
edge of the ligament in three (Lanz Group 0), divided
subligamentously to recurve proximally in one (Lanz Group
1A), perforated the ligament to travel in a separate tunnel in
six specimens (Lanz Group 1B). Accessory motor branches at
the level of the distal edge of the transverse carpal ligament
was seen in two specimens (Lanz Group 2) (10).
Johnson and Shrewsbury found in 8 dissections out of 10
thenar branch of the median nerve entered a definite tunnel
of its own and crossed the transverse carpal ligament (16).
High results recorded by Johnson & Shrewsbury (1970) and
Falconer & Spinner (1985) may be result of including in the
flexor retinaculum part of the fibrotendinous tissue of the
thenar muscles (26).
In sixty cadaver hands, Alizadeh et al. reported 78% median
nerve variations. In 28 (47%) hands recurrent nerve ran an
extraligamentous course (Lanz Group 0), subligamentous in
17 (28.3%) (Lanz Group 1A), transligamentous in 7 (11.7%)
(Lanz Group 1B). The recurrent branch originated from the
ulnar side in 7 (11.7%) cases (Lanz Group 1C) (1).
Steinberg et al. dissected both hands of 23 cadavers. The
nerve was found to course in a normal manner in 33 of 46
(71.7%) upper extremities. The most common variant that
he observed was the recurrent nerve piercing the carpal
ligament 2 to 4 mm proximal to the distal end of the tunnel
in 13 hands (28.3%). An additional branch in the proximal
part of the tunnel was found in 10 (21.7%) hands, following

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Demircay E, et al: Anatomic Variations of the Median Nerve
or total sparing of thenar muscles is possible from the effects
of compression neuropathy of carpal tunnel syndrome with
the presence of these connections. They are also suggested as
causes for unusual motor losses of muscles in the hand after
peripheral nerve lesions (15,18,37).
Variations in Martin – Gruber anastomosis can be classified
by patterns and types. Pattern I comprises cases with one
anastomotic branch, and Pattern II those with two anastomotic
branches. Types a, b, and c are subdivisions depending on the
level of origin of the anastomosis from the median nerve.
Type a originates from the branch of the median nerve to
the superficial forearm muscles. Type b originates from the
median nerve itself and Type c from the anterior interosseous
nerve (18,25,30,37,40). (Table II).
These reports are in part responsible for the shift away from
the previously popular (29) short transverse incision when
surgery is necessary for the carpal tunnel syndrome, because
these anomalous nerve branchings are at jeopardy in the
process of a blind release of the transverse carpal ligament
(10).
endoscopic CTR with single proximal incision (Agee) has
limited visualization, injury to all types of TCDN origins can
be avoided with this technique. An unaware surgeon could
transect, especially Types 1 and 2 of TCDN origin, because
they lie under or just distal to the TCL.
Communications between the median and ulnar nerve in
the forearm is common, its incidence is reported to be about
10 to 23% (18,30,37). They are known as Martin – Gruber
anastomosis after it was first described by Martin in 1763 and
then later by Gruber. They were reported rarely in the distal
forearm and in the palm, between the recurrent branch of the
median and the deep branch of the ulnar nerve (18,30,37).
The majority of these connections cross over from the median
nerve to the ulnar nerve. Connections from ulnar to median
nerve in the forearm are extremely rare (18,30,37). The rarity
of these connections indicates that they are anomalies. They
are referred to as “reverse Martin – Gruber anastomosis” (37).
These anastomoses cause changes in motor conduction
studies, and in the presence of carpal tunnel syndrome, it may
result in unusual findings in evoked muscle potentials. Partial
Figure 4: Variations in the position and the course of the median nerve.

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Demircay E, et al: Anatomic Variations of the Median Nerve
median nerve entrapment syndromes require awareness of
possible involved sites and a detailed knowledge of related
anatomy.
ConCLuSIon
Anatomic variations of the median nerve occur frequently
and may lead to diagnostic confusion and present surgical
risks if not recognized. Successful diagnosis and treatment of
Table I: Median Nerve Variations in the Literature
Alizadeh
46.6
28.3
11.7
11.7
-
Lanz
46
31
23
-
-
Steinberg
-
-
28.3
olave
48.3
18.3
15
16.7
-
Stancic
48
17
16
Beris
-
2.7
Falconer
30
10
60
Extraligamantous (Lanz Group 0)
Subligamantous (Lanz Group 1A)
Transligamantous (Lanz Group 1B)
From ulnar side (Lanz Group 1C)
Supraligamantous (Lanz Group 1D)
Accessory branches of the median nerve at the
distal carpal tunnel (Lanz Group 2)
5
2
1.8
--
18.3 7.338.37 2.7 20
High division of the median nerve
(Lanz Group 3)
Median artery absent (Lanz Group 3A)
Median artery present (Lanz Group 3B)
Accessory lumbrical muscle present (Lanz Group
3C)
2.8
1 1.8
Accessory branches of the median nerve at the
proximal carpal tunnel (Lanz Group 4)
18.3 1.7
Accessory thenar branch running directly in the
then ar muscles (Lanz Group 4A)
21.74
Accessory thenar branch joining another motor
branch first (Lanz Group 4B)
Table II: Variations in Martin – Gruber Anastomosis
Rodrigez-niedenführKazakos Taams Thomson nakashima
Pattern 1
One anastamotic branch
89.5100 10010095.7
Type 1
(originates from the superficial median
nerve to the superficial forearm muscles)
47.37 30.8334.8
Type 2
(median nerve itself)
10.67 194.3
Type 3
(anterior interosseous nerve)
31.687 69.27856.5
Pattern 2
Two anastamotic branch
10.50 4.3

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17. Jeon IH, Kim PT, Park IH, Park BC, Ihn JC: High bifurcation of
median nerve at the wrist causing common digital nerve
injury in endoscopic carpal tunnel release. J Hand Surg Br
27(6):580-582, 2002
18. Kazakos KJ, Smyrnis A, Xarchas KC, Dimitrakopoulou A,
Verettas DA: Anastomosis between the median and ulnar
nerve in the forearm. An anatomic study and literature
review. Acta Orthop Belg 71(1):29-35, 2005
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