Guoyan Zhou; Jiayu Zhou; Danli Wang & Shengbo Yang

The purpose of this study was to reveal the overall distribution pattern of the intramuscular nerves of each extraocular muscle and provide morphological guidance for the selection of the neuromuscular compartment during extraocular muscle transplantation and target localization of the botulinum toxin A injection to correct strabismus. We studied 12 Chinese head specimens that were fixed with formalin. The extraocular muscles from both sides of each head were removed, and a modified Sihler’s staining technique was used to reveal the overall distribution pattern of the intramuscular nerves. We observed an intramuscular nerve-dense region formed by the intramuscular arborized branches in the semitransparent superior rectus, inferior rectus, medial rectus, lateral rectus, superior oblique, inferior oblique, and levator palpebrae superioris muscles with Sihler's staining technique. The seven extraocular muscles can each be divided into two neuromuscular compartments. The intramuscular nerve-dense regions of the superior, inferior, medial, and lateral rectus and the superior oblique, inferior oblique, and levator palpebrae superioris muscles were positioned at 33.50 % –72.72 %, 40.21 % – 66.79%, 37.92 % – 64.51 %, 31.69 % – 56.01 %, 26.35 % – 64.98 %, 40.46 % – 73.20 %, and 27.72 % – 66.07 % of the lengths of the muscle bellies, respectively, and the centers of intramuscular nerve dense regions were located at 59.50 %, 54.18 %, 51.68 %, 50.08 %, 48.38 %, 56.49 %, and 50.77 % of the length of each muscle belly, respectively. The aforementioned values are the means of the actual values. These results suggest that when the strabismus is corrected with muscle transplantation, the extraocular muscle should be transplanted based on the neuromuscular compartment, which would benefit the function of both donor and recipient muscles. The localization of these nerve dense regions is recommended as an optimal target for the injection of botulinum toxin A to treat strabismus.

KEY WORDS: Extraocular muscles; Intramuscular nerve; Distribution pattern; Neuromuscular compartment; Strabismus.

ZHOU, G.; ZHOU, J.; WANG, D. & YANG, S. Overall distribution pattern of the intramuscular nerves of the extraocular muscles and its clinical implications. Int. J. Morphol., 39(5):1412-1419, 2021.