Acta Orthop. Belg., 2005, 71, 29-35
Anastomosis between the median and ulnar nerve in the forearm
An anatomic study and literature review
Konstantin J. KAZAKOS, Anastasios SMYRNIS, Konstantin C. XARCHAS, Alexandra DIMITRAKOPOULOU, From the Orthopaedic Department, Democritus University of Thrace, Alexandroupolis, Greece Anastomosis between the median and ulnar nerve in
and finally in the palm between the recurrent the forearm has been shown to be of clinical signifi-
branch of the median and the deep branch of the cance. We aimed to determine the presence of medi-
an to ulnar nerve communications in the forearm of
Martin (13) was the first to report such an anasto- the Greek population by anatomical studies. At the
mosis in 1763. He described a branch between the same time we defined the types and patterns of the
median and ulnar nerves that “sometimes runs anastomoses found and compared them to those
under the pronator teres muscle”. He also described reported in similar studies that were retrieved after
a wide review of the literature. One hundred and

a connection between median and ulnar nerves in sixty three forearms from 100 cadavers (53 males,
the palm, the “arcus volaris nervorum”. Martin 47 females, 25-91 years old) were carefully dissected
made no comment on the content of these connect- to observe median and ulnar nerve communication.
ing branches, whether they were motor or sensory.
The anastomosis was found in 10 cadavers ; it was
He did not speculate on the final destination of bilateral in 4 and unilateral in 6, on the right side in
their fibers. Gruber (6) was apparently the next to four and on the left side in two. It occurred in 7 of the
mention these findings, in 1870. He dissected 53 male cadavers (14%) and in 3 of the 47 females
212 forearms and found a connection between (6,5%). Overall, the anastomosis was found in 14 of
median and ulnar nerves in 38. The nerve branches the 163 forearms (8,6%). No case of ulnar to median
generally coursed from the median nerve proximal- nerve anastomosis in the forearm was found in
ly to the ulnar nerve distally. Gruber never anatomical examination.
■ Konstantin J. Kazakos, MD, Assistant Professor.
■ Anastasios Smyrnis, MD, Orthopaedic Surgeon.
■ Konstantin C. Xarchas, MD, Lecturer.
■ Alexandra Dimitrakopoulou, MD, Orthopaedic Resident.
nerve are known as the most common form of ■ Dionysios-Alexandros Verettas, MD, Associate “anomalous” innervation. These anastomoses in Orthopaedic Department, Democritus University of Thrace, the forearm and hand provide variations in the innervation of the intrinsic hand muscles, as proved Correspondence : Konstantin C. Xarchas, Democritus Univer- by anatomical and nerve conduction studies (11, 12). sity of Thrace, 6 I. Kaviri rd, 68100 Alexandroupolis, Greece.
Such anastomoses have been reported in the upper part of the forearm, rarely in the distal forearm Acta Orthopædica Belgica, Vol. 71 - 1 - 2005 K. J. KAZAKOS, A. SMYRNIS, K. C. XARCHAS, A. DIMITRAKOPOULOU, D.-A. VERETTAS Fig. 1a and b. — Anastomosis (arrows) between the two nerves arising from the median nerve itself (Type II). UA : Ulnar artery,
MN : Median nerve, A : Anastomosis, UN : Ulnar nerve.
described a branch coursing from the ulnar nerve narrower range of incidence between 10% and proximally to the median nerve distally. This anas- tomosis is referred to as the Martin – Gruber anas- These anastomoses may cause confusion in the tomosis (MGA). It involves axons leaving either diagnosis of conditions affecting the nerve supply the main trunk of the median nerve or the anterior to the intrinsic muscles of the hand. The crossing interosseous nerve, crossing through the forearm to axons may innervate intrinsic muscles supplied by join the main trunk of the ulnar nerve and ultimate- the ulnar nerve, the median nerve or both.
ly innervating the intrinsic hand muscles. This vari-ation has been reported to occur in as many as 15- Table I. — Distribution of the anastomoses between the 31% of subjects (12, 29). Most often the anomalous median and ulnar nerve in the forearm, related to sex and axons innervate the first dorsal interosseous muscle and less often the hypothenar and thenar mus- cles (8). Its reported incidence differs between physiologic and anatomic studies. In the former it has been described as occurring in 5-40% ofcases (12, 8, 4, 27) whereas anatomic studies report a Acta Orthopædica Belgica, Vol. 71 - 1 - 2005 ANASTOMOSIS BETWEEN THE MEDIAN AND ULNAR NERVE IN THE FOREARM Fig. 2a and b. — Anastomosis (arrows) between the two nerves arising from the anterior interosseous nerve (Type III). UA : Ulnar
artery, MN : Median nerve, A : Anastomosis, UN : Ulnar nerve, AIN : Anterior interosseous nerve, FDS : Flexor digitorum superfi-
cialis muscles.
Depending on the level of the nerve injury, an MATERIAL AND METHODS
increased or decreased motor deficit of the intrinsichand muscles can be detected. The knowledge of One hundred fresh frozen cadavers were dissected in these anastomoses and the resulting anomalous the morgue of Athens during a time period of three innervation patterns is of major importance for years. From these, 53 belonged to males and 47 tofemales. Sixty-three cadavers (30 male and 33 female) assessment of traumatic or entrapment lesions of were studied bilaterally and 37 (23 male and 14 female) the median and ulnar nerve (11, 28).
unilaterally. In total, 163 forearms were dissected. The The purpose of our research was to determine age of cadavers ranged from 25 to 91 years. the incidence and also the types of this anastomo- An ‘S’ shaped incision was carried out, covering the sis in the Greek population and compare our results whole anterior surface of the forearm. The superficial to those of similar previous studies. The findings fascia was opened and the flexor carpi ulnaris muscle and literature review are presented, to guide the and tendon mobilised to give full exposure of the ulnar hand surgeon when dealing with forearms with a artery and ulnar nerve. The branches of the ulnar nerve in the forearm were dissected and all possible anasto- Acta Orthopædica Belgica, Vol. 71 - 1 - 2005 K. J. KAZAKOS, A. SMYRNIS, K. C. XARCHAS, A. DIMITRAKOPOULOU, D.-A. VERETTAS moses between median and ulnar nerves were docu- sex and presence or absence of the anastomosis in mented. The level at which the connections joined the the right forearm according to the Pearson test, median and ulnar nerves was measured using the medi- gave the following data : X2 = 0.11 and p = 0.73 ; al epicondyle of the humerus as reference (point 0). The b) the same cross – correlation for the left forearm research was made with the use of magnifying glasses gave the following values : X2 = 4.27 and p = 0.038 (table I). This confirms that absence of the Statistical comparisons were performed in the depart- anastomosis in the left forearm is more rare in ment of statistics in the National School of Public Healthof Athens using the chi-squared test. P < 0.05 was females than in males, or else that the anastomosis regarded as statistically significant.
in the left forearm is 1.2 times more frequent infemales than in males.
nerve were found in 10 out of 100 samples of Anastomoses between median and ulnar nerves cadavers, which were studied. It occurred in 7 of in the forearm are of phylogenetic significance (2).
the 53 male cadavers (3 bilateral and 4 only in the In many mammals and frequently in primates there right forearm) and in 3 of the 47 female cadavers are similar connections between the median and (1 bilateral and 2 only in the left forearm).
ulnar nerve at or below the elbow. Anastomoses Therefore, the anastomosis between the two nerves could be remnants of the common ventral nerve was found in 14 of the 163 forearms, which were trunk innervating flexor muscles in the upper dissected (table I). The incidence in the male fore- extremity, which is noted in the early stages of evo- arms was 14% and 6.5% in the female forearms.
lution. Anastomoses occur frequently in humans These anastomoses were classified into three types and are therefore considered a variation rather than depending on the level of origin of the anastomosis from the median nerve. Type I originates from the It has been estimated that in the forearms of 15% branch of the median nerve to the superficial fore- to 31% of individuals, motor axons descend from arm flexor muscles, Type II from the median nerve the median nerve, crossing to the ulnar nerve, and itself (fig 1) and Type III from the anterior ultimately innervating intrinsic hand muscles interosseous nerve (fig 2). Type I occurred in one which are normally supplied by the ulnar nerve (12, case (n = 1-7%), type II occurred in one case (n = 29). This anastomosis gives rise to changes in motor 1-7%) and type III occurred in 12 cases (n = 12- conduction studies, identifying its presence. When 87%) and the branch passed medially to join the this anastomosis exists in a patient with carpal tun- ulnar nerve in either its upper or middle one-third.
nel syndrome, it may result in unusual findings in The average length of the anastomosis was 6.4 cm. Its origin was on average 6.8 cm distal to There is no consensus in the literature about the the medial epicondyle, and its connection to the classification of anastomosis between the two ulnar nerve was on average 11.0 cm distal to the nerves. Numerous classifications have been medial epicondyle. The anastomosis joined the proposed by Nakashima (14), Hirasawa (9), ulnar nerve as a single branch in twelve cases and Thomson (25), Shu et al (21), Srinivasan and Rhodes split into two branches in two cases. The superior (22) and Rodriguez-Niedenfuhr et al (17) ; their clas- branch had a recurrent course and the inferior one sifications were based on anatomical dissections.
ran downwards. Anastomoses between ulnar nerve Uchida and Sugioka (26), Oh et al (15) and Kimura proximally to the median nerve distally were not et al (11) proposed classifications based on electro- found out, nor were anastomoses between these physiological examinations and Shu (21) proposed another classification based on histological exami- With regard to the analysis of frequency the fol- nations. A summary of these classification schemes lowing were found : a) Cross – correlation between Acta Orthopædica Belgica, Vol. 71 - 1 - 2005 ANASTOMOSIS BETWEEN THE MEDIAN AND ULNAR NERVE IN THE FOREARM Table II. — Classifications of anastomosis between the median and ulnar nerves.(Abbreviation : MN : median nerve, UN : ulnar nerve, AIN : anterior interosseous nerve, TM : thenar muscles, HM : hypothenar muscles, FDP : flexor digitorum profundus mus- Anastomosis
Uchida (20)
Kimura (1)
muscular branchesFDP muscleoriginated fromthe connection The incidence of anastomosis between the two with carpal tunnel syndrome (CTS) and from 15% nerves in earlier reports was 15.2% according to to 39% in either normal or unselected subjects.
Gruber (6), 15.5% according to Thomson (25), Uchida and Sugioka (26) determined the incidence 10.5% according to Hirasawa (9), 15.5% according of anastomosis in patients without and with cubital to Mannerfelt (12), 23% according to Taams (24), tunnel syndrome and found an incidence of 16% in 21.3% according to Nakashima (14), 13.1% accord- the normal controls and 17% in the cubital tunnel ing to Rodriguez-Niedenfuhr et al (17). syndrome group. In other electrodiagnostic studies Mannerfelt (12) was the first to use electrodiag- the highest incidence of the anastomosis was found nostic techniques to detect anastomosis between for the first dorsal interosseous muscle (FDI).
the two nerves and reported a 15% incidence in a Wilbourn and Lambert (29) reported that anomalous study of 41 patients. Crutchfield and Gutmann (4) axons innervate the FDI muscle much more com- found an incidence of 28% in the general popula- monly (95%) than the hypothenar (41%) and thenar tion and 62% in 29 relatives of 5 subjects with muscles (14%). In 22 limbs showing the anastomo- anastomosis. Several other authors, using electro- sis in our study, the anastomotic median axons diagnostic techniques, have reported incidences of innervated the FDI area 21 times, hypothenar mus- anastomosis ranging from 8% to 26% in patients cles in 9 cases and thenar muscles in 3 cases.
Acta Orthopædica Belgica, Vol. 71 - 1 - 2005 K. J. KAZAKOS, A. SMYRNIS, K. C. XARCHAS, A. DIMITRAKOPOULOU, D.-A. VERETTAS Kimura et al (11) studied 656 arms of 328 subjects It has been suggested that unilateral anastomosis using electrophysiological methods and found ana- between the two nerves occurs more often on the stomosis in 57 (17%) subjects and 96 arms (15%).
right side than on the left (24). In our study anasto- The incidence of anastomosis in our study was 8.6%.
moses were also found mainly on the right side in We used the classification of patterns and anatomical examination (four against two).
types (18) to compare our results to those of previ- Crutchfield and Gutmann (4) and Piza-Katzer (16) ous reports. Pattern I comprises cases with one found median-ulnar nerve communication in the anastomotic branch, and Pattern II those with two family members of persons who showed this anastomotic branches. Types a, b, and c are subdi- anomalous connection, and suggested that there is visions depending on the level of origin of the familiar inheritance, probably autosomal dominant.
anastomosis from the median nerve. Type a origi- In the present study, we did not study familiar nates from the branch of the median nerve to the superficial forearm flexor muscles. Type b origi- Occurrence frequency for ulnar to median nerve nates from the median nerve itself and Type c from communication was reported as 5% by Rosen (19) the anterior interosseous nerve. Our results confirm and 16.7% by Golovchinsky (5). In the present that the anastomosis appears as one branch with study, we did not find any ulnar to median com- various origins from the median nerve or its branches, as already described by Thomson (25), No statistically significant difference was found Srinivasan and Rhodes (22) and Taams (24) (table III).
between men and women regarding the frequency Intramuscular anastomosis has also been describ- of these anastomoses. This was an expected result, ed (14, 17), but we found no such anastomosis in view of earlier analyses, which indicated auto- despite the use of magnification during dissection.
somal dominant inheritance of these innervation The course of the anastomosis has been more frequently described as transverse or oblique than There is now electrophysiological evidence that arched (6, 9). We found that the transverse or median – ulnar nerve anastomoses convey motor oblique course depended on whether the anasto- fibers from the median to the ulnar nerve in the motic end at the ulnar nerve was in the superior or forearm for innervation of the intrinsic muscles in the hand (7, 10). These electrophysiological findings At its termination, the anastomosis has been indicate that there is motor communication from recorded either as a single branch or as a single the median to the ulnar nerve in the forearm.
branch which divided into two branches, one with Median nerve stimulation at the elbow evoked not an oblique course and the other with a recurrent only muscle action potentials (MAP) from the course (9). Like Gruber (6), we found a single con- thenar muscles, but also from the hypothenar and nection more frequently than a double one. the first dorsal interosseous muscles.
Table III. — Patterns and types of anastomosis shown by different authors Pattern I
Pattern II
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