Introduction
Approximately 16 million strokes happen globally each year, and in 80% of cases, they lead to motor function impairment and significant challenges in rehabilitation [1]. Upper limb central plegia is one of the many severe complications that can result from a stroke and stroke associated disability is a major medical and social challenge [2].
Globally, annually, peripheral nerve injuries account for 15—40% of all injury cases, and the incidence is 16.9 cases per 100,000 population [3—5]. Injuries to the brachial plexus are less common and account for 0.7% of cases of all road traffic injuries, and the annual incidence per 100,000 population in different countries is as follows: Japan — 0.2, USA — 1.6, Switzerland — 0.3—0.8, Czech Republic and England — 0.2, Serbia — 1.0 and Brazil — 1.5, Scotland — 0.8 [6—9]. Injuries sustained while riding motorcycle, snowmobiles, skis and snowboards all account for 3.0—4.8% of cases, while injuries sustained from brachial plexus in the group of victims with multiple injuries accounts for 4.2—5.0% of cases. According to multiple sources, road traffic accidents are the cause of brachial plexus injuries in 49—95% of cases, and stab and gunshot wounds — 38—47% [10].
Transfer of extraplexus donor nerves is a new approach to treating both central and peripheral nervous systems pathologies. Contralateral transfer of the C7 and L7 nerves has been clinically proven to improve function of the affected upper and lower limbs [11].
Due to the issue of inadequate length, surgeons must use a nerve transplant to replace the deficiency when transferring the C7 spinal nerve contralaterally [12]. In order to accomplish direct anastomosis, surgeons separate the donor nerve as far distally as feasible, up to the point where it connects to other components of the brachial plexus; that is, a complex made up of the anterior division, middle trunk, and C7 spinal nerve is identified [11]. On the other hand, the opposite side’s recipient nerve is split as close to the spinal nerve C7’s egress from the intervertebral foramen as feasible.
Also, to reduce the defect between the contralateral donor nerve and other nerves of the brachial plexus, different surgical routes for transferring the C7 spinal nerve have been developed, divided into intravertebral (extra- and intrathecal), transvertebral (transcorpus, transdiscal, transospinous), retrotracheal (prevertebral, premuscular) and pretracheal (peri-carotid, retrosternocleidomastoid, subcutaneous) [13, 14].
In light of the aforementioned, the purpose of this study is to determine the anatomical circumstances of direct anastomosis during contralateral transfer of the middle trunk and its anterior division, the anterior and posterior roots, and the C7 spinal nerve’s perineural complex.
Material and methods
The department examining corpses at Krasnoyarsk regional Bureau of Forensic Medicine, as well as the departments of operative surgery and topographic anatomy at Krasnoyarsk State Medical University named after Professor V.F. Voino-Yasenetsky and Sechenov University, performed an anatomical study on 105 cadavers of men and women (between the ages of 40 and 97), 24 preparations of the spinal cord, 36 vertebrae, and 121 preparations of the brachial plexus (105 on the right side and 15 on the left).
The bodies were kept in a refrigerator between 3 and 5 degrees Celsius, and it took up to 20 hours from the time of death to the study. Without any damage to the head, neck, upper limbs, or chest, general somatic disorders were the cause of death for every individual. The Krasnoyarsk State Medical University’s ethics committee, which bears Professor V.F. Voino-Yasenetsky’s name, authorized the study protocol (protocol N127/24 of September 25, 2024).
Using a centimeter tape and a caliper, the circumference of the neck at the level of the C7 cervical vertebra was measured as part of the anthropometric analysis of the bodies. Following this, all components of the cervical spine, spinal cord, and brachial plexus were dissected anatomically layer by layer. The C7 cervical vertebra, the C7 spinal cord segment, the radicular filaments, the anterior and posterior roots, the spinal nerves C7, C7, C7, C7, and Th7, as well as the upper, middle, and lower trunks and their anterior and posterior divisions, were isolated. We measured the height, arch. length, the transverse and posteroanterior diameters of the C7 spinal cord segment, the length of its circumference between all grooves, the length of the anterior and posterior radicular threads, the anterior and posterior roots, the angle of their inclination, and the transverse and posteroanterior diameters of the C7 cervical vertebra and the vertebral foramen of the C7 vertebra using a caliper.
The length of the spinal nerve C7, its middle trunk, and its anterior division were measured twice using calipers: once covered with epineurium (epineural level) and again after the removal of the epineurium (perineural level). The C7 spinal nerve’s length was measured from the point where the anterior and dorsal roots (which emerge from the intervertebral foramen) converge to the middle trunk’s conventional border, which is the line that runs across the start of the superior and inferior trunks. The confluence of the spinal nerves C5 and C6, as well as the lower spinal nerves C8 and Th1, marked the start of the upper trunk. The middle trunk’s length was measured from the location where its divisions originate to the traditional border with the C7 spinal nerve. The anterior division’s length was measured from the middle trunk’s bifurcation to the area where it joined the upper trunk’s anterior division, or the start of the lateral fasciculus.
Geometric models of ten surgical pathways for contralateral transfer of the roots, the C7 spinal nerve, the middle trunk, and its anterior division to the position of the C7 spinal nerve on the opposite side were built using drawings of transverse sections of the neck with actual dimensions. This allowed for the measurement of the necessary nerve insertion size, the length of each path, and the frequency of direct anastomosis cases.
The MS Excel 12.0 application (Microsoft Corporation, USA) was used to enter all of the collected data, and Statistica for Windows 12.0 0 (StatSoft, USA) was used to analyze the database that was created. The Shapiro-Wilk test was used to evaluate the indicators for normality of distribution before nonparametric approaches were applied. The median (Me), minimum and maximum values, and quartiles [Q1; Q3] were calculated for each sample indicator; the Mann—Whitney U test was used to identify intergroup differences, and Spearman’s (rs) was used to determine pairwise contingency.
Results
The anatomical characteristics of these formations must be considered when transferring the anterior and dorsal roots of the C7 spinal cord segment intra-vertebrally contralaterally from the healthy side to the location of the roots of the damaged side. According to the study, the C7 cervical vertebra’s transverse foramen has a diameter between 19.5 and 39 mm, with a median of 24.5 [22.0; 26.1] mm and posterior-anterior diameters of 12.7—29.1 and 14.2 [14.0; 14.5] mm. The median circumference of the vertebral foramen is 61.2 [55.6; 66.1] mm, with a range of 51.8 to 70.5 mm. The vertebral body’s foramen circumference segment measures 20.4 [18.5; 22] mm in length, while the arc’s is 40.8 [37.1; 44.1] mm. The foramen is trapezoidal in shape, with a narrow base at the back, opposite the spinous process, and a wide base in front, close to the vertebral body.
There is a segment of the spinal cord C7 in the vertebral foramen. It is oval in shape, has a transverse diameter of 12 to 18 mm, a median of 15 [14; 16] mm, and posterior-anterior diameters of 6—11 and 10 [10; 11] mm. This segment’s circumference has a median of 39.3 [36.1; 40.8] mm and ranges from 31.4 to 43.9 mm. The segment’s circumference measures 6.9 [6.3; 7.2] mm between the posterior radicular threads, 11.1 [10.2; 11.5] mm between the rear and front, and 10.2 [9.4; 10.6] mm between the front ones.
The anterior root filaments leave the spinal cord at an angle of 37.5 [35; 45] degrees from horizontal level, while the posterior ones enter the C7 segment obliquely ascending and exit obliquely descending. In the cervical portion of the spinal cord C7, the anterior radicular filaments are substantially (p = 0.004) shorter than the dorsal ones, measuring 12 [10; 13] mm versus 15 [13; 16] mm. The anterior and posterior roots, which are 14 [11; 15] mm horizontally and pass through the intervertebral foramen, are formed by the filaments of the posterior and anterior roots, which are 13 [12.5; 14] mm from the spinal cord and meet at an angle of 17.5 [10; 20] degrees. The anterior radicular threads and spine are 10—28 mm and 25 [23.5; 26.5] mm long, whereas the dorsal radicular filaments and spine are between 10 and 34 mm long overall, with a median of 28 [25; 30] mm.
The anterior and posterior radicular filaments and roots in the spinal canal (intravertebral tract) can be transferred extradural contralaterally, anteriorly or posteriorly to the spinal cord (Fig. 1). Every technique has pros and cons of its own. Because the vertebral foramen contains right and left triangular spaces, each measuring 19 [11.6; 22.2] mm2, between the spinal cord, body, legs, and lamina of the vertebral arch, the anterior approach enables you to operate in more pleasant conditions (mm2 on each side). Another benefit of the direct intravertebral tract is its proximity to the center of the neck, which runs anterior to the median fissure of the spinal cord, shortening its length.
Fig. 1. Schematic representation of the anterior (A) and posterior (P) intravertebral pathways of contralateral transfer of spinal cord segment roots C7.
CN — the center of the neck; TS — is a triangular space; R — the radius of the circumference of the posterior inside the vertebral pathway.
The length of the selected path, the radicular filaments and roots are crucial for direct contralateral coaptation without nerve implantation. Using the anterior intravertebral tract, the total length of the anterior radicular filaments and the high-frequency root is 3.6 mm longer than the total distance of the spinal cord circumference segment between the anterior radicular filaments on one side (10.2 [9.4; 10.6] mm) and the anterior radicular filaments on the other side (12 [10]; 13] mm) (table). The benefits of employing this operating route with a zero radius from the centre of the neck are confirmed by a comparative analysis on each preparation (n=24). The posterior intravertebral tract is a good choice because of its increased radius of circumference from the centre of the neck and the fact that the root and posterior radicular filaments are longer than necessary for direct anastomosis without nerve insertion.
The spinal nerve C7 is created when the anterior and posterior roots unite as they emerge from the intervertebral foramen. It then travels through the middle trunk before entering the anterior and posterior divisions. The C7 spinal nerve complex, including the middle trunk and its anterior division, is between 45 and 146 mm long overall. Its median length at the epineural level is 71 [63; 78] mm, while it is between 45 and 146 and 75 [67; 84] mm at the perineural level. Thus, it is recommended to remove the epineurium from the donor and perform contralateral transfer of the perineural complex in order to lengthen it (Fig. 2).
Fig. 2. The length of the spinal nerve C7 (1), the middle trunk (2) and the anterior division (3) on preparations of the right brachial plexus covered with epineurium (a) and after removal of the epineurium (b).
There are three methods for trans-vertebral contralateral transfer of the C7 spinal nerve: medially from the intervertebral joints via the interspinous ligament, posteriorly and medial through the vertebral body or intervertebral disc (Fig. 3). According to the study, the C7 cervical vertebra’s body has a transverse diameter of 19.5 to 39 mm, with a median of 29.2 [26.5; 31.1] mm, posterior-anterior diameters of 12.7—29.1 and 17.3 [16; 19] mm, and heights of 12—13.8 and 13 [12.6; 13.6] mm. The highest incidence of direct anastomoses occurs during contralateral transfers of the perineural complex via the transdiscal, interspinous, and transvertebral trans-corpus pathways (Table).
Fig. 3. Schematic representation of the percorporeal (PC) and interosseous (IO) pervertebral pathways of contralateral transfer of the perineural complex of the spinal nerve C7, the middle trunk and its anterior division.
Comparative characteristics of donors and surgical routes for contralateral transfer of roots, epi- and perineural complex of the C7 spinal nerve, middle trunk and its anterior division
| Name of the operational route | Path radius, mm | Donor length (radicular filaments and roots, epi- and perineural complex C7), mm | Path length, mm | Difference between donor and path lengths, mm (+excess/–defect) | Frequency of direct anastomoses, % (excess donor length, in mm) | Frequency of nerve insertion, in % (insertion length, in mm) |
| 1. Intravertebral anterior (n=24) | 0 | filaments and roots 25 [23,5; 26,5] | 21,4 [20,2; 23] | +3,6 | 83,3 (0,6—6,8) | 16,7 (1,4—3,4) |
| 2. Intravertebral posterior (n=24) | 10 [10; 11] | filaments and roots 28 [25; 30] | 21,6 [20,2; 22,5] | +6,9 | 95,8 (0,4—27,9) | 4,2 (0,5) |
| 3. Transvertebral transcorpus (n=36) | 8,6 [8; 9,5] | epi- 71 [63; 78] peri- 75 [67; 84] | 39,8 [37,4; 42,6] | +31,2 +35,2 | 100 (3,4—44,5) 100 (17,8—104,7) | 0 0 |
| 4. Transvertebral transdiscal (n=36) | 8,6 [8; 9,5] | epi- 71 [63; 78] peri- 75 [67; 84] | 37,8 [35,3; 40,6] | +33,2 +37,2 | 100 (4,9—46,9) 100 (20,1—106,9) | 0 0 |
| 5. Transvertebral interspinous (n=36) | 14,2 [14; 14,5] | epi- 71 [63; 78] peri- 75 [67; 84] | 40,8 [37,1; 44,1] | +30,2 +34,2 | 100 (0,1—45,9) 100 (13,9—99,1) | 0 0 |
| 6. Retrotracheal prevertebral (n=36) | 17,3 [16; 19] | epi- 71 [63; 78] peri- 75 [67; 84] | 46,5 [43,7; 49,7] | +24,5 +28,5 | 97,2 (1,4—37,8) 100 (10,6—98,7) | 2,8 (7,1) 0 |
| 7. Retrotracheal premuscular (n=36) | 22,2 [22; 22,5] | epi- 71 [63; 78] peri- 75 [67; 84] | 65,7 [63,1; 69,4] | +5,3 +9,3 | 31 (0,5—18,7) 83,3 (0,1—79,2) | 69 (1—25,2) 16,7 (0,7—8,3) |
| 8. Pretracheal paracarotical (n=121) | 32,6 [29,5; 37,4] | epi- 71 [63; 78] peri- 75 [67; 84] | 63,8 [60; 69,4] | +7,2 +11,2 | 40,5 (0,3—78,8) 81 (0,1—84,1) | 59,5 0,1—51) 19 (0,1—22,3) |
| 9. Pretracheal retrosternocleidomastoid (n=121) | 42,6 [39,5; 47,4] | epi- 71 [63; 78] peri- 75 [67; 84] | 101,6 [94,1; 112,8] | –30,6 –26,6 | 5,8 (1,2—16,9) 8,3 (0,8—43,3) | 94,2 (2,8—131,6) 91,7 (1—76,5) |
| 10. Pretracheal subcutaneous (n=121) | 51,6 [48,5; 56,4] | epi- 71 [63; 78] peri- 75 [67; 84] | 127,5 [120; 138,8] | –56,5 –52,5 | 0 2,5 (0,5—12,6) | 100 (9—157,5) 97,5 (3,2—104,3) |
Both prevertebral and premuscular methods are used to retrotracheally, contralaterally transplant the C7 spinal nerve, the middle trunk, and its anterior division (Fig. 4). In the first, the perineural complex is located around the vertebral body and secondly, first laterally and forward between the anterior and middle scalene muscles and then medially in front of the longus colli muscle on the opposite side. According to a comparative analysis of each specimen (n=36), the perineural complex’s overall length in the first path is always enough for direct anastomosis, whereas in the second path it is 83.3% (Table).
Fig. 4. Schematic representation of the prevertebral (PV) and premuscular (PM) retrotracheal pathways of contralateral transfer of the perineural complex of the spinal nerve C7, the middle trunk and its anterior division.
Pretracheal contralateral transfer of the spinal nerve C7, the middle trunk and its anterior division is carried out in three ways: peri-carotid, retro-sternoclavicular-mastoid and subcutaneous (Fig. 5). One feature of these procedures is that the recipient and donor nerves are moved in various directions towards one another and the length of these transfers varies according to the size of the neck. Human corpses at the level of the C7 cervical vertebra had neck circumferences ranging from 260 to 444 mm, with a median of 340 [320; 370] mm, transverse diameters of 83—142 and 108 [102; 118] mm, and radiuses of 41.4—70.9 and 54.1 [50.9; 58.9] mm, according to the measurements.
Fig. 5. Schematic representation of the paracarotical (PC), retrosternocleidomastoid (RS) and subcutaneous (SC) pretracheal pathways of contralateral transfer of the perineural complex of the cerebrospinal nerve C7, the middle trunk and its anterior division.
A contralateral peri-carotid transfer involves passing the perineural complex subcutaneously between the internal jugular vein and the common carotid artery to reach the contralateral spinal nerve C7. Direct anastomosis is feasible with this technique in 81% of cases, compared to 8.3% for retrosternocleidomastoid and 2.5% for subcutaneous, according to a comparative research on each preparation (n=121).
Accordingly, the study found that direct anastomosis to the recipient nerve is possible when the roots or perineural complex — which includes the C7 spinal nerve, the middle trunk, and its anterior division — are used as a donor in a contralateral transfer. However, the frequency of this anastomosis varies based on the surgical technique. All routes of contralateral transfer occupy unequal segments of circles with varied radii from the centre of the neck according to anthropometric measurements of the neck and its organs and calculations using geometric model creation.
The table indicates that when selecting a surgical path up to 30 mm from the centre of the neck, the length of the epi- and perineural complexes equally permits direct anastomosis to be carried out with a high frequency. The perineural complex considerably (p=0.001) increases the frequency of direct anastomoses 2—2.7 more when the path is chosen to be between 30 and 40 mm from the centre of the neck. In rare instances, direct anastomosis may be performed when performing any donor complex surgically more than 40 mm from the centre of the neck.
According to correlation analysis, the distance from the centre of the neck has an inversely significant functional relationship with the frequency of direct anastomoses between the donor complex and the recipient nerve (Fig. 6). The graph indicates that the frequency of direct anastomoses increases with proximity to the neck’s centre, and this is directly correlated with a reduction in path length (Fig. 7). Its length also has a direct, significant functional relationship with the distance of the path from the centre of the neck in situations when a nerve insertion is necessary and direct anastomosis is not feasible (Fig. 8). All of the graphs show that the frequency of direct anastomosis drops by 10% for every 10 mm that the surgical path is further from the centre of the neck, while the length of the path grows by 20 mm and the length of the nerve insertion increases by 10 mm.
Fig. 6. Graph of the relationship between the radius of the circumference of the operative path and the frequency of direct anastomoses.
Fig. 7. Graph of the relationship between the radius of the circle segment and the length of the operational path.
Fig. 8. Graph of the relationship between the radius of the circumference of the surgical path and the length of the nerve insert.
Discussion
One of the most pressing issues in repairing nervous system damage is determining the shortest, safest, and most efficient path for contralateral transfer of the C7 spinal nerve [14]. The C7 spinal nerve is typically too short for contralateral transfer, and the defect is restored with a nerve transplant. Due to the difficulty of growing through two sutures and the considerable distance that regenerated axons must travel along the graft, there is a significant delay in the manifestation of motor recovery in this instance [15]. Consequently, anatomically based pathways that enable direct anastomoses between the recipient and donor nerves are required.
Over the past three decades, anatomical knowledge regarding some of the C7 spinal nerve’s contralateral transmission channels has been gathered in the literature. This knowledge includes information on the length of the required nerve insertion and the number of potential direct anastomoses [16—18]. However, the length of the C7 spinal nerve and the size of the surrounding anatomical components were not indicated in this information, which was gathered from small-scaled clinical or cadaveric material. This prevents us from determining overall routing patterns, the nature of the correlation between neck diameters and contralateral transfer outcomes, and, consequently, the best surgical approach.
The length of the donor nerve and the length of the path are the two most significant factors in direct anastomosis in contralateral anastomosis, according to our own anatomical investigation using adequate cadaveric material and analysis of the results. We suggest using the perineural complex — which includes the C7 spinal nerve, the middle trunk, and its anterior division — that has been detached from the epineurium as a donor in light of the unequal length. This complex, once isolated from the epineurium, allows for a 2—2.7-fold increase in the frequency of direct anastomoses during contralateral transfer across the pre-tracheal, peri-carotid and retro-tracheal premuscular pathways. It was possible to determine general patterns of path length, frequency of direct anastomoses, and, if required, nerve insertion length by measuring the neck, the C7 cervical vertebra, the cervical segment of the C7 spinal cord, the radicular filaments, the roots, the C7 spinal nerve, the middle trunk, its anterior division, and the geometric models of all paths in full size. It is known that the length of the contralateral donor transfer path decreases the distance from the centre of the neck by 1.1—6 times, the length of the nerve insertion decreases by 5.2—21.7 times, and the frequency of direct anastomoses increases by 1.1—40 times (Table). In contrast, the frequency of direct anastomoses reduces by 10% for every 10 mm that the path is distant from the centre of the neck, while the length of the path grows by 20 mm and the length of the nerve insertion increases by 10 mm.
High-frequency contralateral transmission of radicular filaments and roots is possible via the anterior and posterior intravertebral paths that are most proximal to the neck centre (radius 0—10 mm). This necessitates proximal coaptation to the recipient root and maximal distal isolation of the donor roots at the exit from the intervertebral foramen. In contrast to our results, Jiang S. et al. consistently employed a nerve insert 10 mm in length for suturing the front roots and 20 mm for the posterior ones during intravertebral intradural coaptation [16]. The inability to fully isolate the donor root’s length using this technique is clearly linked to the variations in the outcomes. The intravertebral extradural pathway allowed Yang K. et al. to completely isolate the donor root and perform direct anastomosis with the recipient root in all 9 corpses [17].
The most convenient conditions for executing direct anastomoses are created by transvertebral tracts, which are also executed at a minimal distance from the centre of the neck (radius 8.6—14.2 mm). Our findings support the findings of Y.F. Wang et al., who used a route through the vertebral body to accomplish direct anastomosis in 15 cadavers on both sides in every instance [14]. V. Vanaclocha et al. used the transdiscal method to achieve direct anastomosis in all 10 cases on human cadavers [19]. J.Guan et al. used the posterior interspinous tract to accomplish direct anastomosis in all ten of their patients to date [20].
In addition to enabling high-frequency direct anastomosis, the retrotracheal tracts are situated 17.3—22.2 mm from the centre of the neck. A direct anastomosis was carried out in every instance when P. Li et al. and W.D. Xu used the retrotracheal prespinal tract on cadavers and ill patients [21, 22]. Only two individuals had direct coaptation of nerves utilising the retrotracheal premuscular tract, and in six of those cases, L. Xu et al. employed a nerve insert that was 30—85.6 mm long [14]. According to H. Pen et al., two patients also received a 40 mm sural nerve graft during the procedure [23].
The likelihood of direct anastomosis is significantly decreased by the pretracheal tracts’ significant distance (32.6—51.6 mm) from the neck’s centre. Y.C. Bhatt and P.B. Doshi. All 10 individuals had direct nerve coaptation using the near-sleeping pathway [24]. Perhaps the nerve tension during the approach is what produced such a high outcome.
The pretracheal sternocleidomastoid and subcutaneous surgical paths are the longest, according to several publications, and do not permit direct anastomosis; instead, a 78—200 mm long sural nerve graft or clavicle and humerus shortening are necessary [25—27].
A nerve insert with a length of 0.5—25.2 mm and 1—104.3 mm is therefore needed in cases where direct anastomosis is not possible. Therefore, all surgical routes for transferring the contralateral perineural complex of the C7 spinal nerve, the middle trunk, and its anterior division, performed at a distance of up to 40 mm from the centre of the neck, allow direct anastomosis in 81—100% of cases, more than 41 mm—2.5—8.3%.
Conclusion
Contrary to the epineural division, the frequency of direct anastomoses during contralateral transfer through the retrotracheal premuscular and pretracheal periocarotid tracts can be increased by 2—2.7 times by using the C7 spinal nerve, the middle trunk, and its anterior division as a donor for the perineural complex.
Surgical procedures for contralateral transfer of the middle trunk, anterior division, and perineural complex of the spinal nerve C7, carried out up to 40 mm from the centre of the neck, permit direct anastomosis in 83—100% of cases and more than 41 mm — 2.5—8.3%.
The length of the surgical path increases by 20 mm, the length of the nerve insertion increases by 10 mm, and the frequency of direct anastomosis reduces by 10% for every 10 mm that the surgical path is removed from the middle of the neck.
Participation of authors:
Concept and design of the study — Gorbunov N.S.
Statistical processing of the data, text writing — Kasparov E.V., Kober K.V., Rostovtsev S.I., Vasil’ev Yu.L., Nikishaev B.Yu.
Data collection and processing — Gorbunov N.S., Kasparov E.V., Kober K.V., Rostovtsev S.I., Lebedeva D.N.
Editing — Thamae N.E., Gorbunov N.S., Dydykin S.S.
Compliance with ethical principles. The study was approved by the local ethics committee of Krasnoyarsk State Medical University (protocol № 127/24 of September 25, 2024)