The Ligamentum condylicum posterius as a precursor structure of the Processus condylicus posterior, another Proatlas‐Manifestation of the human occipital bone

Abstract

This article presents the results of a dissection series investigating a previously neglected ligamentous structure attached to the human occipital bone, the Ligamentum condylicum posterius or posterior condylar ligament, and relates these results to the manifestation of a likewise poorly recognized occipital bony variation, the Processus condylicus posterior. The dissection of 50 human cranio‐cervical junctions revealed the existence of the posterior condylar ligament in 98% of all cases, sometimes containing free elongated ossicles and osseous spurs at the insertion points at the occipital bone. In two cases the osseous formation of a Processus condylicus posterior became apparent (4%), which further provided the opportunity to study the behaviour of the ligament in these cases. In this article, we show and discuss that the posterior condylar ligament and osseous structures possibly derive from tissue that originates from the material of the dorsal arch of the Proatlas, a rudimentary vertebra between occipital bone and atlas. For this purpose, the Ponticulus atlantis posterior as another Proatlas‐manifestation, whose origin from the dorsal Proatlas‐arch is widely accepted in literature, is considered. This bony variant was found in 11 specimens (22%) in the present study and further served to classify and interpret the findings of the much rarer Processus condylicus posterior. As a result of this dissection series and a review of literature on this understudied topic, a typology of manifestations of the posterior condylar ligament, Processus condylicus posterior and related structures like free ossicles has been introduced.

Proposing novel dorsal Proatlas‐manifestations: Description and classification of three rare phenomena in humans

“…The third phenomenon observed is of interest in so far as we have predicted the existence of such or similar case in the past (Wolf‐Vollenbröker & Prescher, 2021). In that study, we dealt with the different stages of manifestation of the dorsal Proatlas, ranging from a fibrous strand that bridges the condylar fossa (posterior condylar ligament) to free ossicles lying in the course of this ligament and to osseous processes that can be explained by (partial) ossification and failure of regression of the material of the dorsal Proatlas (=parts of posterior Proatlas‐arch).…”

“…Due to its similar topographic conditions (cf. Figures 2,12), possible clinical symptoms in cases of manifestation of this unknown spur may be comparable to the possibilities in the cases of a posterior condylar process or posterior ponticle, which can be briefly summarized by common neurological (e.g., headache, migraine cervicale, pain in neck and shoulder) or vascular (e.g., vertebral artery dissection) syndromes or symptoms (Pekala et al, 2018, Wolf-Vollenbröker & Prescher, 2021. A possible underlying pathomechanism is the irritation of the vertebral artery and accompanying (sympathetic) nerval structures in its V3-segment, which runs caudally in relation to the osseous process.…”

“…In that study, we dealt with the different stages of manifestation of the dorsal Proatlas, ranging from a fibrous strand that bridges the condylar fossa (posterior condylar ligament) to free ossicles lying in the course of this ligament and to osseous processes that can be explained by (partial) ossification and failure of regression of the material of the dorsal Proatlas (=parts of posterior Proatlas‐arch). We presented a classification of these dorsal Proatlas‐manifestations related to that ligament: Types I–V (Wolf‐Vollenbröker & Prescher, 2021). For a comprehension of these results, see Table 1.…”

“…Also, Proatlas‐rudiments exist that are found as free ossicles at the CCJ like the ossiculum terminale persistens [Bergmann], the paracondylar mass (e.g. Torklus & Gehle, 1975), and as recently assumed by us as free postero‐ or retrocondylar ossicles (Wolf‐Vollenbröker & Prescher, 2021).…”

“…The human craniocervical junction (CCJ) is an anatomically variable region (Christ, 1990; Prescher, 1997), which offers a wide range of morphological peculiarities. Occasionally, new macroanatomical findings and their clinical relevance are brought to light (Sacher et al, 2019; Spittank et al, 2016; Tsuang et al, 2011; Wolf‐Vollenbröker & Prescher, 2021; Zumbihl et al, 2022). However, the interpretation of new findings requires precise knowledge of the previous results, which are manifold and difficult to overview due to the long history of studying the anatomical details of the CCJ by morphological disciplines.…”