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Year : 2014  |  Volume : 47  |  Issue : 1  |  Page : 95--101

Cadaveric study of anatomical variations of the median nerve and persistent median artery at wrist

Pawan Agarwal, Shivkant Gupta, Prashant Yadav, D Sharma 
 Department of Surgery, Plastic Surgery Unit, N.S.C.B. Government Medical College, Jabalpur, Madhya Pradesh, India

Correspondence Address:
Pawan Agarwal
292/293 Napier Town, Jabalpur - 482 001, Madhya Pradesh
India

Abstract

Background: Awareness of anatomical variations of the median nerve at wrist is important in repair of traumatic injuries and treatments of compression syndrome because in these situations precise dissection of the nerve is mandatory and such variations are not infrequent. Materials and Methods: In this study, 52 hands of 52 fresh cadavers were dissected and median nerve anatomy along with the presence of persistent median artery (PMA) was noted. Results: A total of 26 hands (50%) had the deviation from the standard text book anatomy of the median nerve. There was early division of the median nerve into the medial and lateral branches in 11.53% hands. There was early branching of the 2 nd common digital nerve in 9.6% hands. The transligamentous motor branch to the thenar muscle was most prevalent (42.3% hands). The single motor branch to the thenar muscles was found in the majority of hands (84.6%). The PMA was present in 11.53% hands and it was associated with variations in the median nerve anatomy in all cases. Conclusions: This study shows a high percentage of deviation from standard anatomy as well as a high percentage of transligamentous thenar muscle motor branch. The presence of PMA was associated with variations in the median nerve anatomy in all cases. Therefore if PMA is present there are very high chances of associated median nerve anomalies.



How to cite this article:
Agarwal P, Gupta S, Yadav P, Sharma D. Cadaveric study of anatomical variations of the median nerve and persistent median artery at wrist.Indian J Plast Surg 2014;47:95-101


How to cite this URL:
Agarwal P, Gupta S, Yadav P, Sharma D. Cadaveric study of anatomical variations of the median nerve and persistent median artery at wrist. Indian J Plast Surg [serial online] 2014 [cited 2019 Aug 19 ];47:95-101
Available from: http://www.ijps.org/text.asp?2014/47/1/95/129632


Full Text

 Introduction



Awareness of anatomical variations of the median nerve at the wrist is important in repair of traumatic injuries and treatment of compression syndrome because in these situations, precise dissection of the nerve is mandatory and such variations are not infrequent. [1] The knowledge of variation will prevent damage to the median nerve during the surgical release of the carpal tunnel in patients of carpal tunnel syndrome and reduces on table confusion in cases of the median nerve injury. Standard anatomical books states that at wrist median nerve enters the carpal tunnel deep to the flexor retinaculum and reaches the palm beyond the distal border of flexor retinaculum and divides into lateral and medial branches. [2] The lateral branch gives off a recurrent muscular branch to supply the three thenar muscles and then subdivides into three proper palmar digital nerves to supply the two sides of the thumb and radial side of the index finger. The branch to the index finger provides a branch to the first lumbrical. The medial branch subdivides into two common palmar digital nerves, lateral and medial. The lateral common nerve gives a branch to the second lumbrical and subdivides to supply the adjacent sides of the index and middle finger. The medial common nerve receives a communicating branch from the superficial branch of the ulnar nerve and then subdivides to supply the adjacent sides of the middle and ring finger [3],[4] [Figure 1].{Figure 1}

There are few, if any, clinical and electrophysiological clues indicating anatomic variations. [5] Therefore, indirect evidences should be sought to anticipate the median nerve anomalies. Awareness of anatomic variations of the median nerve and presence of persistent median artery (PMA) should be a part of the preoperative planning, in order to avoid the risk of the median nerve injury or incomplete decompression at operation. This study was conducted to determine the incidence of variations in the median nerve as well as incidence of PMA at the wrist in fresh cadavers.

 Materials and Methods



This study was conducted in the plastic surgery unit, Department of Surgery and Forensic Medicine NSCB Medical College, Jabalpur (MP) over the period of 2 years. Before the commencement of study approval from institutional ethical committee was taken. All cases with congenital anomalies, deformities and injuries to the hand and wrist were excluded from the study. A total of 52 hands of 52 cadavers were dissected in this period. Only one hand (left) of each cadaver was dissected except in cadaver in which the right hand was dissected due to injury to the left hand. 13 cadavers were females and 39 cadavers were male. The hand dissection was started with an incision on the distal palmar crease and continued in the crease on the thenar eminence, skin flaps were raised and superficial palmar fascia was dissected to expose the superficial palmar arch (SPA) and the proper digital branches of the median nerve these branches were traced proximally to the distal margin of the flexor retinaculum which was incised and carpal tunnel was exposed, Median nerve was identified and then traced 15 cm proximally from flexor retinaculum up to the division of the common digital nerve to proper digital nerve distally. The branches to the thenar eminence were dissected carefully and if these branches traversed the flexor retinaculum they were released from the flexor retinaculum. The presence of PMA was also noted. The size of median artery was not measured, but a PMA was identified as a grossly visible unnamed artery which has a definite course running along the median nerve in the forearm and hand. Any variation if present were noted and photographs were taken. Lanz's classification system was used to analyse our data. The data from our study and from Lanz and Tountas study were compare by proportion test (z test) to analyses the results and difference were considered the significance if P < 0.05.

 Results



Over a period of 2 years, 52 hands of 52 cadavers were dissected. There was no statistically difference for any variation based upon sex. 26 hands showed anatomy which was according to the standard textbook of anatomy while 26 hands had some variations. We found the following variations in the median nerve anatomy [Table 1].{Table 1}

Out of 52 hands 8 hands (15.38%) were in the Lanz group 1 (variations in the thenar eminence motor branch), 2 hands (3.84%) belong to the Lanz group 2 (accessory branch distal to flexor retinaculum), 6 hands (11.53%) in Lanz group 3 (high division of the median nerve) and only one hand (1.92%) in Lanz group 4 (accessory branches proximal to flexor retinaculum).There was early division of the median nerve into the medial and lateral branches in 6 hands (11.53%) [Figure 2]. Distance of division of nerve proximal to flexor retinaculum ranges from 1.5 cm to 10 cm. There was early branching of the 2 nd common digital nerve in 5 hands (9.6%) in the middle or the distal forearm. Distance of branching proximal to flexor retinaculum ranges from 5 cm to15 cm [Figure 3].We found 7 hands (13.24%) having 2 branches to the thenar eminence 1 hand (1.92%) had 3 branches to the thenar eminence and rest 44 hands (84.6%) had only one branch to the thenar muscles [Figure 4] and [Figure 5].Out of 52 hands 22 hands (42.3%) had transligamentous branch (branch to the thenar eminence through the transverse carpal ligament). 19 hands (36.5%) had extraligamentous branch (branch emerging distal to transverse carpal ligament) and 11 hands (21.15%) had subligamentous branch (branch emerging below the transverse carpal ligament) [Figure 6],[Figure 7] and [Figure 8].In this study, we found that 9 hands (18.12%) had communicating branches between the sensory branches of the median nerve. The communication was most commonly found between the two proper digital branches to the thumb (5 hands-9.61%), the two common digital branches (3 hands-5.77%) and a communicating branch between the medial branch of proper digital nerve for the thumb and proper digital nerve to the index finger in one hand (1.92%) [Figure 9] and [Figure 10].The incidence of the PMA was 11.53% (6 hands) [Figure 3]. In none of specimen PMA was substituted for radial artery. The presence of PMA was associated early division of the median nerve, early branching of second common digital nerve and multiple branches for thenar eminence in all cases [Table 2].{Figure 2}{Figure 3}{Figure 4}{Figure 5}{Figure 6}{Figure 7}{Figure 8}{Figure 9}{Figure 10}{Table 2}

 Discussion



With the exception of the palmar cutaneous branch, the median nerve does not usually give off branches in the distal third of the forearm. Significant variation of the median nerve appears to be uncommon and most major anatomy textbooks make no reference to such variations. [4],[6]

Although the anatomical variations are recently classified, there are still different kinds of anomalies that can be seen. [1] Thus, surgeons should take such anatomical variations into consideration in order to plan appropriate surgical approaches. Variations at the level of the carpal tunnel are particularly common with one operative study reporting an abnormal configuration of the median nerve in 52.3% of wrists studied. [7] Our study also report relatively higher incidence of anatomical variations (50% hands).

Lanz described the variations in the median nerve anatomy as 46%, 7.5%, 2.9% and 2.9% in Lanz group I to IV respectively. Lenz did not report on type I variation but rather quotes Poisel's findings for group I which involve the study of 100 cadaver hands. [8] Lenz studied group II, III and IV variations in a series of 246 hands.

In our study, only 32.69% hands were classified according to Lanz classification. 15.38% were in the Lanz group I, 3.84% belong to the Lanz group II, 11.53% in Lanz group III and only 1.92% in Lanz group IV [Table 3]. Lanz also described the pattern of motor branch to thenar muscles as 46% extraligamentous, 31% were subligamentous and 23% were transligamentous. Our study found the high incidence of transligamentous branches (42.3%) which was statistically significant (P < 0.05) while extraligamentous and subligamentous were present in 36.55% and 21.15% of hands which was statistically insignificant (P > 0.05). Lanz described accessory branch distal to carpal tunnel in 7.5% of hands while in our study, it was present in 3.84% of hands (statistically significant P < 0.05). High division of the median nerve and accessory branch proximal to carpal tunnel was found in 2.9% and 1.6% of Lanz study while it was present in 11.5% and 1.92% of our study (statistically insignificant P > 0.05) [Table 3]. In a study by Ahn (354 cases) the extraligamentous was the most common type 340 cases (96.1%). [9] {Table 3}

Tountas reported the incidences as 0.37%, 0.97% and 0.97% from Lanz group II to IV respectively. Tountas found the high incidence of extraligamentous branches (96.7%) while transligamentous and subligamentous were present in 1.21% and 2.07% of hands. Our study found the high incidence of transligamentous branches (42.3%) while extraligamentous and subligamentous were present in 36.5% and 21.15% of hands (statistically significant P < 0.05). High division of the median nerve was found in 11.5% of our study while it was present in only 0.97% of Tountas study (statistically significant P < 0.05). If we compare accessory branch proximal or distal to carpal tunnel there was no statistical difference in two studies [Table 3].

In the Lanz group 1 (variation in the thenar eminence motor branches), multiple branches to thenar muscles were found in 8 cases (15.3%), 2 branches to the median eminence in 7 cases (13.24%) 3 branches to the thenar eminence muscles in 1 (1.92%) case and 44 (84.6%) cases had only one branch to the thenar muscles. The study conducted by Ahn in 354 cases the incidence of multiple branches was 10.5%. Only one motor nerve branch was found in 89.5% of patients and multiple branches were found in 10.5% of patients.

In a survey of 3300 operated cases of carpal tunnel syndrome, Castorina et al. [10] in their study have reported just eighteen cases of high duplication of the median nerve while in our study, there was high duplication of the median nerve in 6 hands (11.53%).

In literature, the incidence of PMA ranges from 2.2% to 27.1% respectively. [11],[12],[13]

Henneberg and George observed the presence of median artery providing substantial blood supply to hand in 96 dissected forearms of 15 adult African females and 49 adult males. They found the highest incidence (27.1%) of PMA than previously reported by any author. They did not find any significant difference in its occurrence between sexes or between right and left limbs. [12]

A study by Claassen et al. found large median artery in 7.4% cases. The median arteries took their origin from the ulnar artery or the common interosseous artery. In one case, the median artery pierced the median nerve in its course under the pronator teres. The outer diameters of the median arteries varied between 1.5 mm and 2.0 mm. The radial arteries were not replaced in any of their cases with a large median artery. [13]

Natsis et al. found two unilateral cases of PMA originating from the ulnar artery along with high division of the median nerve before entering the carpal tunnel. Such an artery may result in several complications such as carpal tunnel syndrome, pronator syndrome, or compression of the anterior interosseous nerve. Therefore, the presence of a PMA should be taken into consideration in clinical practice. [14]

Nayak et al. investigated the presence of the PMA and its contribution in the formation of SPA in 42 cadavers (84 upper limbs) of Indian origin. The PMA was found in 15.4% and of these 11.9% the PMA took part in the formation of SPA and in three instances (3.5%), the PMA did not make up part of the SPA. The outer diameters of the median arteries varied between 0.8 and 2.6 mm with the mean value of 1.7 mm. [15]

Gassner et al. examined 100 wrists and distal forearms of 50 asymptomatic volunteers with ultrasonography and colour Doppler ultrasonography. A PMA was found in 26% cases with a mean diameter of 1.1 mm. In 63% of hands, the PMA was associated with high division of the median nerve or a bifid nerve configuration in the carpal tunnel. They conclude that a PMA has a superficial course close to the transverse carpal ligament; pre-operative diagnosis of this anatomic variation may be of clinical importance. [16]

We have not measured the size of median artery. This artery supplies only median nerve along with other adjacent arteries. Muscular branches from radial and ulnar arteries also contribute to supply median nerve. The median artery should not be dissected away from the nerve otherwise it may lead to necrosis and degeneration of the median nerve. In our study, the incidence of the PMA was 11.53% and its presence was associated with anomalies of the median nerve in all cases. Anomalies of the median nerve includes the early branching of the median nerve, early branching of second common digital nerve and multiple motor branching to the thenar muscles. Eiken et al. discussed three instances of a major division of the median nerve high in the forearm out of a total of 359 carpal tunnel explorations. In two of these instances, a median artery was interposed between the branches. [17]

The clinical importance of the persistence of this artery at the wrist is well-documented as a cause of the carpal tunnel syndrome. Due to the fact that this artery is responsible for the arterial supply to the median nerve and the neighbouring muscles and in some cases for the thumb and radial side of the index finger, its damage could have serious affects to blood circulation of the forearm and hand. In our study, we found that 9 hands (18.12%) had communicating branches between the sensory branches of the median nerve. Communications between different branches may lead to the preservation of function in cases of complete transaction of a particular branch of the median nerve and incomplete decompression of the median nerve in cases of compression neuropathy.

The results of this study denotes that there is a high incidence of transligamentous branch of the median nerve, which may be damaged during release of carpal tunnel and presence of PMA will be associated with high chances of anomalies of the median nerve anatomy.

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