Intramuscular Distribution of the Abducens Nerve in the Lateral Rectus Muscle for the Management of Strabismus

ABSTRACT

Aims: To elucidate the intramuscular distribution and branching patterns of the abducens nerve in the lateral rectus (LR) muscle so as to provide anatomical confirmation of the presence of compartmentalization, including for use in clinical applications such as botulinum toxin injections.

Methods: Thirty whole-mount human cadaver specimens were dissected and then Sihler’s stain was applied. The basic dimensions of the LR and its intramuscular nerve distribution were investigated. The distances from the muscle insertion to the point at which the abducens nerve enters the LR and to the terminal nerve plexus were also measured.

Results: The LR was 46.0 mm long. The abducens nerve enters the muscle on the posterior one-third of the LR and then typically divides into a few branches (average of 1.8). This supports a segregated abducens nerve selectively innervating compartments of the LR. The intramuscular nerve distribution showed a Y-shaped ramification with root-like arborization. The intramuscular nerve course finished around the middle of the LR (24.8 mm posterior to the insertion point) to form the terminal nerve plexus. This region should be considered the optimal target site for botulinum toxin injections. We have also identified the presence of an overlapping zone and communicating nerve branches between the neighboring LR compartments.

Conclusion: Sihler’s staining is a useful technique for visualizing the entire nerve network of the LR. Improving the knowledge of the nerve distribution patterns is important not only for researchers but also clinicians to understand the functions of the LR and the diverse pathophysiology of strabismus.

KEYWORDS:

• Abducens nerve
• branching pattern
• compartmentalization
• intramuscular nerve distribution
• lateral rectus
• Sihler’s stain

Acknowledgments

We are grateful to Kwan-Hyun Youn, PhD, a medical illustrator ([email protected]) for the illustrations. We also thank the donors who donated their bodies for research at the Department of Anatomy and Institute for Applied Anatomy at the Konkuk University.

Declaration of interest

None of the authors has any proprietary/financial interest. No conflicting relationship exists for any author.

Additional information

Funding

This work was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF)funded by the Ministry of Science [grant number 2017R1D1A1B03035444].

Notes on contributors

Hyun Jin Shin

Hyun Jin Shin designed this study and wrote the manuscript.

Shin-Hyo Lee

Shin-Hyo Lee collected the data and drew the illustration.

Kang-Jae Shin

Kang-Jae Shin collected the data.

Ki-Seok Koh

Ki-Seok Koh revised this manuscript.

Wu-Chul Song

Wu-Chul Song designed this study and revised this manuscript.