Location of the myoneural junction of the inferior oblique muscle: An anatomic study

Abstract

Purpose: To examine both the horizontal and vertical locations of the myoneural junction of the inferior oblique muscle (IOM) in reference to the ala nasi, IOM origin, and inferior orbital rim.

Materials and methods: Fifty-six orbits from 56 Japanese cadavers (15 male and 41 female cadavers; average age at time of death, 86.5±9.4 years) were used in this experimental anatomical study. The inter-alae-nasi distance and the horizontal distances from the ipsilateral ala nasi to the IOM origin (ala-nasi-origin distance) and to the myoneural junction (ala-nasi-junction distance) were measured. The horizontal distance from the IOM origin to the myoneural junction (origin-junction distance) was calculated by subtraction of the ala-nasi-origin distance from the ala-nasi-junction distance. The vertical distance from the inferior orbital rim to the myoneural junction (rim-junction distance) was also measured.

Results: The ala-nasi-junction, origin-junction, and rim-junction distances were 12.2±3.2mm, 10.6±3.2mm, and 3.4±1.0mm, respectively. Males had a longer inter-alae-nasi distance than females (P<0.001), although the other distances did not show statistically significant sex-related difference (P>0.050). The ala-nasi-junction distance tended to be negatively correlated with the inter-alae-nasi distance (r=-0.222, P=0.050).

Conclusions: The ala-nasi-junction distance can be affected by the inter-alae-nasi distance, which was found to be longer in males. Therefore, the IOM origin and the inferior orbital rim can be considered as more practical and reliable reference points to predict the location of the myoneural junction during the posterior inferior orbitotomy, irrespective of sex.

Keywords: Ala nasi; Inferior oblique muscle; Inferior oblique muscle origin; Inferior orbital rim; Myoneural junction.