Intramuscular Nerves of the Inferior Rectus Muscle: Distribution and Characteristics

ABSTRACT

Purpose

Knowledge of the distribution of intramuscular nerves of the extraocular muscles is crucial for understanding their function. The purpose of this study was to elucidate the intramuscular distribution of the oculomotor nerve within the inferior rectus muscle (IRM) using Sihler’s staining.

Method

Ninety-three IRM from 50 formalin-embalmed cadavers were investigated. The IRM including its branches of the oculomotor nerve was finely dissected from its origin to the point where it inserted into the sclera. The intramuscular nerve course was investigated after performing Sihler’s whole-mount nerve staining technique that stains the nerves while rendering other soft tissues either translucent or transparent.

Results

The oculomotor nerve enters the IRM around the distal one-fourth of the muscle and then divides into multiple smaller branches. The intramuscular nerve course finishes around the distal three-fifth of the IRM in gross observations. The types of branching patterns of the IRM could be divided into two subcategories based on whether or not topographic segregation was present: (1) no significant compartmental segregation (55.9% of cases) and (2) a several-zone pattern with possible segregation (44.1% of cases). Possible compartmentalization was less clear for the IRM, which contained overlapping mixed branches between different trunks.

Conclusion

Sihler’s staining is a useful technique for visualizing the gross nerve distribution of the IRM. The new information about the nerve distribution and morphological features provided by this study will improve the understanding of the biomechanics of the IRM, and could be useful for strabismus surgery.

KEYWORDS:

• Inferior rectus muscle
• intramuscular nerve distribution
• sihler’s stain
• oculomotor nerve
• botulinum toxin injections

Acknowledgments

The authors express their gratitude to the donor cadavers and their families who participated in the medical school cadaveric donation program.

None of the authors has any proprietary/financial interest

No conflicting relationship exists for any author.

Contributors

Hyun Jin Shin designed this study and wrote the manuscript

Shin-Hyo Lee collected the data

Tae-jun Ha collected the data

Wu-Chul Song designed this study and revised this manuscript

Andrew G. Lee revised this manuscript

Ki-Seok Koh designed this study and revised this manuscript

Additional information

Funding

This work was supported by the This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MSIT) [No. 2019R1F1A1059435].