DOI: 10.33962/roneuro-2021-035 C7 contribution to the ulnar nerve. Literature review L.P. de Macêdo, A.U. Netto, K. Franke, P.V. Oliveira Eugenio, L.R. de Moraes Freitas, F.A.S. de Lima Júnior J.V.R. de Paula, S.N. Bernardino, F.H.M. de Souza, N.S. Almeida, H.R.C. Azevedo-Filho Romanian Neurosurgery (2021) XXXV (2): pp. 215-218 DOI: 10.33962/roneuro-2021-035 www.journals.lapub.co.uk/index.php/roneurosurgery C7 contribution to the ulnar nerve. Literature review L.P. de Macêdo1, A.U. Netto1, K. Franke1, P.V. Oliveira Eugenio2, L.R. de Moraes Freitas2, F.A.S. de Lima Júnior2, J.V.R. de Paula3, S.N. Bernardino4, F.H.M. de Souza5, N.S. Almeida1, H.R.C. Azevedo-Filho6 1 Department of Neurosurgery, Hospital da Restauração, Recife, Pernambuco, BRAZIL 2 Centro de Ciências Médicas, Universidade Federal da Paraíba, João Pessoa, Paraíba, BRAZIL 3 Faculdade Pernambucana de Saúde, Recife, Pernambuco, BRAZIL 4 Neurophysiologist, Department of Neurology, Hospital Getúlio Vargas, Recife, Pernambuco, BRAZIL 5 Chief of Peripheral Nerves Section, Department of Neurosurgery, Hospital da Restauração, Recife, Pernambuco, BRAZIL 6 Chairman of Department of Neurosurgery, Hospital da Restauração, Recife, Pernambuco, BRAZIL ABSTRACT Introduction. Classic anatomical literature frequently describes C7 contribution to ulnar nerve (UN) formation as a casual event. However, surgical practice and dissections frequently reveal a recurrent presence of a lateral cord component of the UN. This study aimed to seek through literature to establish the frequency and degree of this contribution. Methodology. We ran a literature review searching on Pubmed, MEDLINE, Embase and Web of Science databases for ulnar nerve anatomy and described discursively the results. Results and discussion. We found 9 articles that described quantitatively and qualitatively the contribution of C7 on the formation of the UN. The prevalence described ranged from 2 to 100%, depending on the methodology used and population characteristics. When present, studies described a contribution from 9,9% to 30,4%, sending even more fibres than T1 root on average. Conclusion. The C7 root can be considered a frequent and important component of the ulnar nerve, explaining UN territory repercussions on C7 radiculopathies. This knowledge is important on surgical approaches, maybe avoiding iatrogenic lesions and negative outcomes. INTRODUCTION The anatomical literature reports the origin of the ulnar nerve (UN) as the medial fascicle (C8-T1), but often receiving fibers from the ventral branch of C7. It is also mentioned its path through the axilla, initially Keywords ulnar nerve, brachial plexus, neuroanatomy Corresponding author: Lívio Pereira de Macêdo Hospital da Restauração, Recife, Pernambuco, Brazil livio21@gmail.com Copyright and usage. This is an Open Access article, distributed under the terms of the Creative Commons Attribution Non–Commercial No Derivatives License (https://creativecommons .org/licenses/by-nc-nd/4.0/) which permits non- commercial re-use, distribution, and reproduction in any medium, provided the original work is unaltered and is properly cited. The written permission of the Romanian Society of Neurosurgery must be obtained for commercial re-use or in order to create a derivative work. ISSN online 2344-4959 © Romanian Society of Neurosurgery First published June 2021 by London Academic Publishing www.lapub.co.uk http://www.lapub.co.uk/ 216 L.P. de Macêdo, A.U. Netto, K. Franke et al. medial to the axillary artery and between this and the vein, continuing distally medial to the brachial artery up to the middle third of the arm, where the UN punctures the medial intermuscular septum and leans medially as it descends anteriorly to the medial head of the triceps muscle towards the interval between the medial epicondyle and the olecranon, with the superior ulnar collateral artery. Its relationship with the brachial artery and medial epicondyle makes it easy to map in its proximal path; a line from the medial epicondyle to the lateral margin of the pisiform bone represents its distal path1,2,3,4,5. Although its path and function are known, there are few records in the literature about the frequency and the way C7 contributes to the formation of the UN. It should also be noted that there are differences between the anatomical study and the electromyographic diagnosis of the nerve. The objective of this study was to seek, through a literature review, to clarify the frequency and the degree of C7's contribution to the formation of the UN. METHODS An integrative review of the literature was carried out, seeking articles that described qualitatively and/or quantitatively the formation of the UN from the brachial plexus. For this, we searched at MEDLINE, Embase and Web of Science, using the descriptors "Ulnar Nerve" and "Anatomy", with no language or publication date restrictions. The results of the search were discursively described. RESULTS AND DISCUSSION Hur et al. (2013) analyzed 100 brachial plexus (BP) from Korean adult cadavers. The extracted samples were immersed in Guanidine-HCl for 2 weeks. After the contribution of C7 was proven, 20 samples were processed with a routine histological staining (H&E) procedure to count the number of myelinized axons using Imbroglio Modometer software. In all 100 BPs, there was a contribution of C7 to the formation of the ulnar nerve. Moreover, it was unanimous the ramification of the C7 fascicles in the distal portion of the fascicles that compose the lateral root of the median nerve, decussing with the medial root of the median nerve. The contribution of C7 to the ulnar nerve was 1.452 ± 429 (9.9%) myelinized axons, C8 was 11.448 ± 1.473 (78.3%) and T1 was 1.720 ± 382 (11.8%) in the 20 samples processed in H&E6. In contrast, Fuss (1989) investigated 158 BPs and reported in his study a 56% contribution of C7 to the formation of the ulnar nerve, highlighting that this collaboration may be accompanied by fibers of the median nerve (type 1) or may occur separately (type 2). Considering the 56:44% relationship between ulnar nerves with and without lateral root, the author highlights that both possibilities should be considered as normal variations7. Pyun, Kang and Kwon (2010), after dissection of 38 BPs, reported 13.1% contribution of C7. It is worth mentioning that, for having performed an associated electrophysiological study, this study showed a high prevalence of alterations in the electromyography of M. flexor ulnar carpi in patients with C7 radiculopathy (13/17 = 76.5%)8. Kumar and Ranganath (2014) also described only 1 (2%) out of 100 BPs with the contribution of the lateral cord of C7 to the formation of the UN; more precisely, the branches for the UN came from the union of the medial and lateral roots of the median nerve9. Guru et al. (2015) dissected 50 upper limbs to observe UN variations. In all, 4 variations were observed, all on the right side. The notable contribution of the BP side cord to the formation of the UN was observed unilaterally in 2 (4%) members. The contributing branch passed from the lateral side to the medial side deeply to the formation of the median nerve and joined the ulnar nerve at its lateral aspect. In the two remaining cases, the ulnar nerve had abnormal communications with the neighboring nerves, radial nerve, and medial cutaneous nerve of the forearm nerve10. Emamhadi et al. (2016) dissected 64 fresh BPs in order to evaluate possible anatomical variations, excluding damaged specimens or ante mortem surgical interventions. During the investigations, it was found collaboration of the lateral cord of BP for the formation of the UN in 3 (9.38%) of the 32 cadavers11. Koo and Lee (2007) analyzed the composition of the terminal branches of BP, dissecting 32 upper limbs. Regarding the UN, four different patterns were observed. The most frequent type was C7, C8 and T1 (75% of cases). In the average diameter, C8 was the thickest, measuring 2.64 ± 0.57 mm, and T1 was the thinnest with 0.06 ± 0.56 mm12. 217 C7 contribution to the ulnar nerve The oldest studies found, performed with even more rudimentary cadaveric dissection techniques, were those of Harris (1904)13 and Linell (1921)14, which showed the presence in, respectively, 86% and 57% of the brachial plexus of an exchange of fibers between the medial and lateral plexus strands, specifically the C7 fibers contributing to the formation of the ulnar nerve. Author, Date Sample (n) Methodol ogy Qualitative Analysis Quantitative Analysis Hur et al., 2013 100 BPs H&E + Imbroglio Modomet er 100 (100%, C7) 1,452 ± 429 (9,9%) axônios Koo, Lee, 2007 32 BPs Cadaveric dissection 24 (75%, C7) 1,18 ±0.59 mm Fuss, 1989 158 BPs Cadaveric dissection 56% (lateral cord) N/A Pyun et al., 2010 38 BPs Cadaveric dissection 13,1% (lateral cord) N/A Kumar, Ranganat h, 2014 50 BPs Cadaveric dissection 1 (2%,lateral cord) N/A Guru et al., 2015 50 BPs Cadaveric dissection 2 (4%, lateral cord) N/A Emamhad i et al., 2016 64 BPs Cadaveric dissection 3 (9,38%,latera l cord) N/A Ramchan dran et al., 2006 1 BP Case Report 1 (lateral root of the median) N/A Linnel, 1921 42 BPs Cadaveric dissection 57%, C7 N/A Harris, 1904 60 BPs Cadaveric dissection 86%, C7 N/A Figure 1. Summary of the findings of the review on C7 contribution It is noticeable that the studies that performed quantitative analysis, especially Hur et al. (2013) and Koo and Lee (2007), showed a higher prevalence of C7 contribution than the studies with cadaveric dissection, except for those of Harris (1904) and Linnel (1921) 6,12,13,14. This can be justified by an eventual iatrogenic loss of the lateral contribution during dissection or by the sophistication of quantitative methods. In this context, it is frequent a sub-quantification of the contribution of C7 to the nerve during dissection, justifying the absence of root representation in most of the classic anatomic literature 1,2,3,4,5. In practice, however, the repercussions of C7 radiculopathies on electromyographic variables in part of the UN territory can be seen, as Pyun et al. (2010) have shown8. This knowledge becomes essential in neurosurgical practice, since unadvised dissection can cause iatrogenicity. The authors themselves came across the contribution of the lateral cord to the formation of the UN during surgical dissection in the treatment of a brachial plexopathy (Figure 2), which motivated this review. Figure 2. CONCLUSION The C7 root can be considered a frequent component of the ulnar nerve, although its contribution may be underestimated in less sophisticated dissection studies. There is even a high incidence of C7 radiculopathy causing repercussions in the nerve territory. Knowledge of this participation is indispensable for peripheral nerve surgery, avoiding iatrogenic lesions and possible negative outcomes for the patient. REFERENCES 1. Baehr M, Frotscher M. Duus Topical Diagnosis in 218 L.P. de Macêdo, A.U. Netto, K. Franke et al. Neurology. 5th ed. Rio de Janeiro, RJ: Guanabara Koogan; 2014. 2. Ellis H. Clinical Anatomy: A Revision and Applied Anatomy for Clinical Students. 8th ed. London: Blackwell Scientific Publications; 1992: 209. 3. Moore KL, Dalley AF. Clinically Oriented Anatomy. 5th ed. Baltimore: Lippincott Williams & Wilkins; 2006: 777. 4. Romanes GJ. Cunningham’s Textbook of Anatomy. 12th ed. New York, NY: Oxford University Press; 1981: 328- 329. 5. Standring S. Gray’s Anatomy. 39th ed. Edinburgh: Elsevier Churchill Livingston; 2005: 847-877. 6. Hur MS, Woo JS, Kim HJ, Lee KS. Frequency and Quantity of the C7 Contribution to the Ulnar Nerve. Korean J Phys Anthropol. 2013;26(3):101-104. 7. Fuss FK. Die Radix lateralis des Nervus ulnaris [The lateral root of the ulnar nerve]. Acta Anat (Basel). 1989;134(3):199-205. 8. Pyun SB, Kang S, Kwon HK. Anatomical and electrophy- siological myotome corresponding to the flexor carpi ulnar is muscle. J Korean Med Sci. 2010; 25:454-57. 9. Kumar SV, Ranganath P. Morphology of the ulnar nerve in axilla and arm and its variations. Int J Anat Res. 2014;2(4):677-680. 10. Guru A, Kumar N, Ravindra Shanthakumar S, et al. Anatomical Study of the Ulnar Nerve Variations at High Humeral Level and Their Possible Clinical and Diagnostic Implications [published online July 12, 2015]. Anat Res Int. doi:10.1155/2015/378063 11. Emamhadi M, Chabok SY, Samini F, et al. Anatomical Variations of Brachial Plexus in Adult Cadavers; A Descriptive Study. Arch Bone Jt Surg. 2016;4(3):253-258. 12. Koo JH, Lee KS. Anatomic Variations of the Spinal Origins of the Main Terminal Branches of the Brachial Plexus. Korean J Phys Anthropol. 2007;20(1):11-19. 13. Harris W. The True Form of the Brachial Plexus, and its Motor Distribution. J Anat Physiol. 1904;38(Pt 4):399-422. 14. Linell EA. The Distribution of Nerves in the Upper Limb, with reference to Variabilities and their Clinical Significance. J Anat. 1921;55(Pt 2-3):79-112. 15. Ramachandran K, Kanakasabapathy I, Holla SJ. Multiple variations involving all the terminal branches of the brachial plexus and the axillary artery – a case report. Eur J Anat. 2006;10(3):61-66.