Objectives: The inferior external occipital bone (IEOB) has a unique morphology region which articulates with another uniquely shaped bone from the apex of the vertebral column awkwardly termed 1st cervical vertebrae (1stCV). 1stCV is recognized to share no features of a typical cervical vertebrae, and thus warranting further investigation. Structurely, 1stCV resembles the occipital bone, which is demonstrated in axial scans. Functionally, it operates with the skull, rather than with the cervical spine. In structure and function it could be termed the occipital vertebrae which is the inferior articulation with the IEOB region which is the superior articulation of the occipital joint (OJ). Craniovertebral joint (CVJ) is a rather broad term versus OJ with superior and inferior articulations of occipital named bones (IEOB and occiptal vertebrae). Study objective is to analyze morphology from osteology, radiology and dissections of IEOB and 1stCV challenging any awkward terms, current beliefs, teachings to confirm OJ.
Methods: Literature search of IEOB and 1stCV revealed they are structurally and functionally similar, not uniquely different as currently taught and perceived. Imaging and osteology observations/measurements was conducted on CT/MRI, GAX-specimens (n=6 skulls/C1vertebrae and formalin-fixed cadavers (FFD) n=31.
Results: Synovial joints represent direct connections between the skull and 1stCV allowing range of flexion-extension, but joint shape prevents axial rotation. As the head rotates via the transverse plane, 1stCV is obliged to move with it. Toltech bilaminar imaging revealed anatomy supporting an OJ or CVJ consisting of IEOB and occipital vertebrae. Understanding the anatomy of the OJ is important for all healthcare providers who interact with the head and neck to acquire airways, conduct surgery, manipulating upper vertebrae/spine, stablilizing the head and neck, and medical technology companies designing safer head and neck equipment.
Conclusions: This study revealed 1stCV is awkwardly and perhaps confusingly named as this bone clinically and morphologically integrates with the IEOB region deserving the term occipital vertebrae forming a new named joint-OJ, or at least be termed the occipital vertebrae as inferior articulation of the CVJ.
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