An anatomical study of the orbital floor in relation to the infraorbital groove: implications of predisposition to orbital floor fracture site.

PURPOSE: To examine the anatomy of the orbital floor in relation to the infraorbital groove.

METHODS: Twenty-two Japanese cadavers aged 86.9 ± 6.0 years at death were used. We examined whether the bony overhang on the infraorbital nerve extending laterally was connected to the segment medial to the infraorbital groove. The bone thicknesses at 1, 2, and 3 mm anterior to the junction between the infraorbital groove and the inferior orbital fissure were measured along the groove. We examined the angle between the infraorbital groove and the orbital floor, both at the medial and lateral margins, at the thinnest point in the above three measurement points. We used the measurement values examined in the left orbits to prevent doubling the number of the orbits.

RESULTS: The bony overhang was not connected to the medial segment in 19 (86.4 %) orbits. The thickness at the thinnest point was thinner in the medial portion (1.02 ± 1.20 mm) than in the lateral portion (2.60 ± 1.82 mm; p = 0.001). The angle between the medial margin and the orbital floor was obtuse (156.5° ± 12.3°), compared with that of the lateral margin (104.0° ± 17.0°; p < 0.001).

CONCLUSIONS: The results of this study imply that the medial portion has an anatomical weakness and few supportive structures. Although these findings were obtained only from Japanese cadavers, there may be associated with frequent occurrences of an orbital floor fracture just medial to the infraorbital groove.