Anatomical Variation and Morphometric Study on Foramen Transversarium of the Upper Cervical Vertebrae in the Thai Population

Abstract

Study design: Foramen transversarium (FT) and foramen arcuale (FA) of upper cervical vertebrae (C1 and C2) in the Thai population were investigated for variation and morphometry.

Purpose: This study aimed to reveal the morphometry of FT and FA in the Thai population.

Overview of literature: The FT and FA are structures found in the upper spine that support the vertebral neurovascular system. Clinically, the surgical approaches to achieve upper cervical stability can be affected by spine variations. FT and FA morphometries have been documented to vary by nationality. However, such reports have been limited in the Thai population.

Methods: The FT and FA of dried C1 and C2 vertebrae (identified bones; n=107, males=53 and females=54) were observed and measured using a Digital Vernier Caliper (Mitutoyo, Kawasaki, Japan). Anteroposterior (AP) and transverse diameters of the left and right FTs (n=214) were measured and compared between sexes. Variations and types of FT and FA found on the upper vertebrae were recorded and classified.

Results: The FT shape of the Thai C1 was AP elliptical, while of that of C2 was transverse elliptical. Compared to females, both diameters of the upper spine were significantly greater in males except for the AP diameter of C2 on the right side. All diameters were significantly different in both sexes and sides except for the AP diameter of C1 and C2. A common type of FT classified in C1 was type 2 (male [69.81%], female [79.63%]) whereas for C2 it was type 1 (male [63.21%], female [59.26%]). Moreover, an incomplete osseous bridge was a major FA subtype observed in the Thai spine.

Conclusions: FT morphometry has an elliptical shape and diameters are greater in males. The FT and FA variations identified in this study will be useful for surgeons treating vertebral neurovascular injuries of the posterior upper cervical spine in the Thai population.

Keywords: Cervical upper spine; Classification; Foramen arcuale; Foramen transversarium; Variation.

Fig. 1

Showing inferior view of upper cervical spines (A, C) and measurement of foramen transversarium diameters (B, D). C1, atlas; C2, axis AP; AP, anteroposterior dimeter; T, transverse dimeter.

Fig. 2

Showing variations of foramen transversarium from C1 at superior (A–C) and lateral (D–F) views. (A, D) Showing bilateral complete FA on both sides of the posterior arch indicated by arrows. (B, E) Showing unilateral complete FA on either side of the posterior arch. (C, F) Showing IOB at the posterior arches indicated by short arrow. Scale bar=2 cm. FA, foramen arcuale; COB, complete osseous bridge; IOB, incomplete osseous bridge.

Fig. 3

Inferior view showing representative variations of FT in C1. (A) Trilateral accessory FT. (B) Bilateral accessory FT. (C) Unilateral accessory FT. (D) Hypoplasic FT. Arrows indicated accessory foramens. Scale bar=2 cm. FT, foramen transversarium.

Fig. 4

(A–E) Classification of the foramen transversarium investigated in this study. T1, type 1 (round); T2, type 2 (elliptical with anteroposterior); T3, type 3 (elliptical with transverse); T4, type 4 (elliptical with oblique from right); T5, type 5 (elliptical with oblique from left). Scale bar=0.5 cm.