Research Article | Open Access | Peer Reviewed

Guyon Canal Anatomy and Ulnar Nerve Arborization Variations: A Cadaveric Anatomic Study

Filomena Ferreira1, Rómulo Silva1, Pedro Pereira2, André Pinho3, Dulce Madeira2

1Orthopaedic department of Unidade Local de Saúde Alto Minho, Viana Do Castelo, Portugal

2 CINTESIS/ Anatomy Unit, Medicine department of Faculdade Medicina Universidade Porto, Porto, Portugal

3 Orthopaedic department of Centro Hospitalar São João EPE/ CINTESIS/ Anatomy Unit, Medicine department of Faculdade Medicina Universidade Porto, Porto, Portugal

  • Abstract
  • Full Text
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ABSTRACT

Introduction: Guyon’s canal precise anatomic boundaries are yet subject of discussion. However, there is agreement that the proximal and medial limit is the pisiformis bone and that the hook of hamate defines its lateral and distal limit.

Symptoms of ulnar neuropathy depend on the location of the compression. It is important to understand its anatomy and potential variability during surgery to explore and decompress this space.

Materials and Methods: We did an anatomic study with 16 wrists from 8 cadaveric specimens. Guyon’s canal diameter and the division pattern of the ulnar nerve inside the canal were evaluated.

Results: The mean diameter of Guyon canal was 8,8 mm, and the mean distance from the pisiformis to the division of the cubital nerve was 1,0 mm. The canal’s content was evenly distributed-50% divided into two branches (motor and common sensitive) and the other half divided into three branches (1 motor and 2 sensitive).

Conclusions: There are very few reports doing this kind of measurements. We must emphasize the great variability in the distance between the pisiformis and the division of the cubital nerve that requires attention at the time of surgical exploration and decompression. More studies are needed to understand the correlation between signs/symptoms and the division pattern within the canal.

KEYWORDS

anatomy, Guyon’s canal, ulnar nerve, variations

INTRODUCTION

The eponym “Guyon Canal” was introduced when Jean Guyon, a French surgeon, first described the ulnar tunnel at the wrist.1 There is still discussion about the exact anatomic boundaries of the ulnar tunnel.1-4 There is consensus that the medial and proximal border is the pisiformis bone and that laterally and distally it ends at hook of hamate; the roof is the volar carpal ligament with the transverse carpal ligament being the floor of the tunnel.1 Inside the tunnel runs the cubital artery and nerve with great anatomical variability.5

Nerve compression in this rigid and limited fibro-osseous tunnel is common, which may occur due to hamate fractures, ganglion cysts, repetitive minor trauma, artery aneurisms, tumour, or as an idiopathic situation .5,6

The ulnar nerve has sensitive and motor functions. The motor branch runs more radially to turn around the medial side of the hook of hamate and reach the deep palmar space to innervate all the fifth finger intrinsic muscles, third and fourth lumbricals, all the dorsal and volar interosseous muscles and the adductor pollicis muscle. The sensitive branch goes distally over the hypothenar muscles and is responsible for the volar sensation of the fifth and cubital half of the fourth finger.2,7

Compression symptoms depend on which part of the nerve is being compressed, underlining the importance of the anatomy and its variability.2,3,8-12

Traditionally, ulnar tunnel has been divided into three zones, according to which part of the nerve is compressed, and the accordingly symptoms: sensitive and motor, just sensitive or just motor.1,2

Zone 1: Proximal to ulnar nerve bifurcation-compression in this area results in sensitive alterations, strength loss and muscle atrophy.

Zone 2: From the bifurcation to the hypothenar muscles arcade, at the radial zone of the tunnel. Includes ulnar motor branch and ulnar artery, thus compression on this zone causes mainly motor symptoms.

Zone 3: After the bifurcation, in the cubital area. Contains ulnar sensitive branch, with symptoms manifesting as hypoesthesia and paraesthesia.

The previously defined zones are established by the anatomic limits of the nerve itself, being quite susceptible to where bifurcation occurs-inside or outside the canal. This influences the causes of nerve and artery compression and, as a result, the signs and symptoms manifested by patients. Therefore, it is crucial to understand and dominate the anatomic variability of this area. This paper pretends to be a morphological study of the Guyon Canal.

MATERIALS AND METHODS

The authors performed an anatomic dissection study using 8 cadavers from a university anatomy lab, and studied a total of 16 wrists. The Guyon canal’s diameter was evaluated, measuring from the pisiformis lateral border until the medial side of hamate’s hook. The major aim of this study is to evaluate the ulnar nerve division pattern inside the canal, whether the motor and sensitive branches arise proximal, distal or inside the canal. For this, the distance between the pisiformis and the nerve bifurcation site was measured (Figure 1). Values were considered negative or positive based on whether the division was proximal or distal to pisiformis. We also registered if the sensitive branch divided inside the canal or not.

FIGURE 1 Guyon canal diameter measure: from the pisiformis lateral border until the medial side of hamate’s hook.

RESULTS

Using anatomic references previously referred, we found a Guyon’s canal mean diameter of 8,8 mm (standard deviation 2,1). Mean distance from pisiformis to ulnar nerve division was 1,0 mm (standard deviation 6,0), ranging from 15 mm proximal to 9 mm distal (Figure 2 and 3).

FIGURE 2 Nerve branching proximal to Guyon’s canal (green needle marks nerve division and the orange ones are at the osseous margins of the canal).

FIGURE 3 Nerve branching inside Guyon’s canal (green needle marks nerve branching and the orange ones are at the osseous margins of the canal).

FIGURE 4 A tripartite nerve inside Guyon canal (needles are marking the different nerve branches).

In 6 hands (37,5%) cubital nerve branched proximally to the canal. We also looked for the bifurcation location of the sensitive nerve branch if that occurred inside tunnel, the ulnar nerve was bipartite (just motor and common sensitive branches), if outside it was tripartite (motor and sensitive branch already divided into common digital nerve to 4th and 5th finger and the cubital digital nerve to 5th finger). An equal distribution was verified, with 50% bipartite and 50% tripartite nerves (Figure 4).

DISCUSSION

Proper understanding of anatomic variability helps surgeons to better understand patient symptoms related to ulnar nerve compression and ensure that an adequate planning and decompression is effective in solving patient complains. There are very few previous reports about this subject. The authors decided to use as anatomic references to measure the ulnar tunnel diameter-the pisiformis lateral border and the hook of hamate’s medial border-because we considered that this distance represents better the real space available for structures inside it. The diameter found (8,8 mm) brings to light the narrowness of the available space inside the canal, explaining the occurrence of nerve compression even with small anomalous structures inside it. There are no other reports to our knowledge using these informations, although Ombaba et al.2 described a proximal tunnel diameter of 11 mm, which is similar to our values. Pierre-Jarome et al.5, performed MRI studies in 250 wrists, measuring Guyon’s canal cross sectional area and described a mean area of 33 and 45 mm2 at proximal and distal parts of the canal, respectively. Other articles measured the length of the ulnar tunnel (proximal to distal) and described values from 40 to 45 mm.2,10

We must emphasize the great variability found in the distance between the pisiformis and the ulnar nerve division (mean 1,0 mm, SD 6 mm: from 15 mm proximal to 6 mm distal to pisiformis). Few studies mention this measure, but report similar variability.2,10

The content of the ulnar tunnel has been previously studied: Fadel et al.3 mentions that 66-86% cases presented bipartite nerve inside canal compared to 13-22% tripartite ones. Nitsu et al.4 in an MRI study shows a 30% prevalence of trifurcated nerve leaving Guyon canal and also characterizes the branching pattern. In our study, we found higher prevalence of tripartite nerve inside the tunnel, which focuses the importance of careful exploration of the entire nerve branching during surgery. Ombaba et al.2 and Depukat et al.10, both suggest that when a patient is considered to surgery, all zones should be explored, regardless of the motor and/or sensitive symptoms.

To understand if the pattern and site of nerve embranchment influences the signs and symptoms presented by patients, more and different studies are needed.

CONCLUSION

More studies are necessary in this matter to confirm these results. The Guyon canal is a very narrow tunnel for the artery and ulnar nerve to pass, thus it is easy to understand that even small tumours, fractures, cysts, inflammatory process or anatomic variances can compress the structures inside. Surgical treatment to free the ulnar artery and nerve may be the unique effective treatment in severe cases, therefore, the extensive anatomic knowledge about this area and its variance is crucial for a successful surgery.

CONFLICT OF INTEREST

There is no conflict of interest to declare.

REFERENCES

  1. Maroukis BL, Ogawa T, Rehim SA, Chung KC. Guyon canal: the evolution of clinical anatomy. J Hand Surg Am. 2016;40(3):560-565.
  2. Ombaba J, Kuo M, Rayan G. Anatomy of the ulnar tunnel and the influence of wrist motion on its morphology. J Hand Surg. 2010;35(5):760-768.
  3. Fadel ZT, Samargandi OA, Tang DT. Variations in the anatomical structures of the Guyon canal. Plast Surg. 2017;25(2):84-92.
  4. Niitsu M, Kokubo N NS. Variations of the ulnar nerve in Guyon’s canal: in vivo demonstration using ultrasound and 3 T MRI. Acta Radiol. 2010;51(8):939-946.
  5. Pierre-Jerome C, Moncayo V TM. The Guyon’s canal in perspective: 3-T MRI assessment of the normal anatomy, the anatomical variations and the Guyon’s canal syndrome. Surg Radiol Anat. 2011;33(10):897-903.
  6. Murata K, Shih JT TT. Causes of ulnar tunnel syndrome: a retrospective study of 31 subjects. J Hand Surg Am. 2003;28(4):647-651.
  7. Bachoura A JS. Ulnar tunnel syndrome. Orthop Clin North Am. 2012;43(4):467-474.
  8. Konig P, Hage J, Bloem J PL. Variations of the ulnar nerve and ulnar artery in Guyon’s Canal: a cadaveric study. J Hand Surg. 1994;19(A):617-622.
  9. Dodds A, Hale D JT. Incidence of anatomic variants in Guyon’s canal. J Hand Surg. 1990;15(A):352-355.
  10. Depukat P, Michael B, Patrick H, et al. Anatomical variability and histological structure of the ulnar nerve in the Guyon’ s canal. Arch Orthop Trauma Surg. 2017;137(2):277-283.
  11. Murata K, Tamai M GA. Anatomic study of variations of hypothenar muscles and arborization patterns of the ulnar nerve in the hand. J Hand Surg Am. 2004;29(3):500-509.
  12. Murata K, Tamai M GA. Anatomic study of arborization patterns of the ulnar artery in Guyon’s canal. J Hand Surg Am. 2006;31(2):258-263.

TABLES & FIGURES

FIGURE 1 Nerve branching proximal to Guyon’s canal (green needle marks nerve division and the orange ones are at the osseous margins of the canal).

FIGURE 2 Nerve branching proximal to Guyon’s canal (green needle marks nerve division and the orange ones are at the osseous margins of the canal).

FIGURE 3 Nerve branching inside Guyon’s canal (green needle marks nerve branching and the orange ones are at the osseous margins of the canal).

FIGURE 4 A tripartite nerve inside Guyon canal (needles are marking the different nerve branches).

 

REFERENCES

  1. Maroukis BL, Ogawa T, Rehim SA, Chung KC. Guyon canal: the evolution of clinical anatomy. J Hand Surg Am. 2016;40(3):560-565.
  2. Ombaba J, Kuo M, Rayan G. Anatomy of the ulnar tunnel and the influence of wrist motion on its morphology. J Hand Surg. 2010;35(5):760-768.
  3. Fadel ZT, Samargandi OA, Tang DT. Variations in the anatomical structures of the Guyon canal. Plast Surg. 2017;25(2):84-92.
  4. Niitsu M, Kokubo N NS. Variations of the ulnar nerve in Guyon’s canal: in vivo demonstration using ultrasound and 3 T MRI. Acta Radiol. 2010;51(8):939-946.
  5. Pierre-Jerome C, Moncayo V TM. The Guyon’s canal in perspective: 3-T MRI assessment of the normal anatomy, the anatomical variations and the Guyon’s canal syndrome. Surg Radiol Anat. 2011;33(10):897-903.
  6. Murata K, Shih JT TT. Causes of ulnar tunnel syndrome: a retrospective study of 31 subjects. J Hand Surg Am. 2003;28(4):647-651.
  7. Bachoura A JS. Ulnar tunnel syndrome. Orthop Clin North Am. 2012;43(4):467-474.
  8. Konig P, Hage J, Bloem J PL. Variations of the ulnar nerve and ulnar artery in Guyon’s Canal: a cadaveric study. J Hand Surg. 1994;19(A):617-622.
  9. Dodds A, Hale D JT. Incidence of anatomic variants in Guyon’s canal. J Hand Surg. 1990;15(A):352-355.
  10. Depukat P, Michael B, Patrick H, et al. Anatomical variability and histological structure of the ulnar nerve in the Guyon’ s canal. Arch Orthop Trauma Surg. 2017;137(2):277-283.
  11. Murata K, Tamai M GA. Anatomic study of variations of hypothenar muscles and arborization patterns of the ulnar nerve in the hand. J Hand Surg Am. 2004;29(3):500-509.
  12. Murata K, Tamai M GA. Anatomic study of arborization patterns of the ulnar artery in Guyon’s canal. J Hand Surg Am. 2006;31(2):258-263.

Conflict of Interest
There is no conflict of interest to declare.

License: This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.

Copyright: © 2021. The Author(s). Article is published by Carpel Press.

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