Morphological analysis and morphometry of the occipital condyle and its relationship to the foramen magnum, jugular foramen, and hypoglossal canal: implications for craniovertebral junction surgery

Abstract

Anatomical knowledge of the occipital condyle (OC) and its relationships to surrounding structures is important for avoiding injury during craniovertebral junction (CVJ) surgeries. This study was conducted to evaluate the morphology and morphometry of OC and its relationship to foramen magnum, jugular foramen (JF), and hypoglossal canal (HC). Morphometric parameters including length, width, height, and distances from the OC to surrounding structures were measured. The oval-like condyle was the most common OC shape, representing for 33.0% of all samples. The mean length, width and height of OC were 21.3±2.4, 10.5±1.4, and 7.4±1.1 mm, respectively. Moreover, OC was classified into three types based on its length. The most common OC length in both sexes was moderate length or type II (62.5%). The mean distance between anterior tips and posterior tips of OC to basion, and opisthion were 11.5±1.4, 39.1±3.3, 25.2±2.2, and 27.4±2.7 mm, respectively. The location of intracranial orifice of HC was commonly found related to middle 1/3 of OC in 45.0%. JF was related to the anterior 2/3 of OC in 81.0%, the anterior 1/3 of OC in 12.5%, and the entire OC length in 6.5%. These morphological analysis and morphometric data should be taken into consideration before performing surgical operation to avoid CVJ instability and neurovascular structure injury.

Keywords: Craniovertebral junction instability; Hypoglossal canal; Jugular foramen; Neurovascular injury; Occipital condyle.

Fig. 1

Inferior view of the skull base. (A) Right occipital condyle showing occipital condyle width (OC-W), occipital condyle length (OC-L), and occipital condyle height (OC-H). Left occipital condyle showing the distances from anterior and posterior tips of occipital condyle (OCAT and OCPT) to basion (Bas) and opisthion (Op). (B) Right occipital condyle showing the relationship of jugular foramen (JF) and occipital condyle, the location of extracranial orifice and intracranial orifice of hypoglossal canal (L-eHC, L-iHC) related to occipital condyle. Left occipital condyle showing the distances from posterior tip of occipital condyle (OCPT) to iHC, eHC and posterior most end of jugular foramen (pJF). FM, foramen magnum; HC, hypoglossal canal; a1/3, anterior one third; m1/3, middle one third; p1/3, posterior one third.

Fig. 2

Photographs showing eight shapes of occipital condyle. (A) Type I, oval-like condyle. (B) Type II, kidney-like condyle. (C) Type III, S-like condyle. (D) Type IV, eight-like condyle. (E) Type V, triangle condyle. (F) Type VI, ring-like condyle. (G) Type VII, two-portioned condyle, and (H) Type VIII, deformed condyle.