Bifid Anterior and Posterior Arches of Atlas

Abstract

Understanding of the pathogenesis and mechanical alterations in cases with a bifid arch of atlas can assist in evaluating the clinical implications and in conduct of surgery.

Tuberculosis of craniovertebral junction: Role of facets in pathogenesis and treatment

“…[2] Like in cases with bifid atlas, the shift of balance on the contralateral side and the obliquity of the inclination of the facet of atlas in the atlantoaxial joint can result in its lateral dislocation over the facet of axis. [5] Distraction of the facets of the atlas and axis, reduction of lateral dislocation, and unilateral fixation of lateral masses can result in effective stabilization of the region.…”

Craniovertebral Junction Instability: A Review of Facts about Facets

“…Musculoskeletal changes associated with basilar invagination like short neck, torticollis, platybasia, Klippel-Feil abnormalities, and spondylotic spinal changes are manifestations of chronic and subtle atlantoaxial instability [ 19 20 ]. The instability is more often of types 2 and 3 facetal dislocation.…”

“…The instability is more often of types 2 and 3 facetal dislocation. Following atlantoaxial fixation, all these secondary musculoskeletal alterations have a potential for reversal in the immediate postoperative phase [ 19 20 ]. This fact suggests that the musculoskeletal alterations are not congenital defects or a result of embryonic dysgenesis, but are a manifestation of chronic instability, and essentially have a protective function.…”

External syrinx introduction of a new term

“…The very fact that Chiari 1 malformation extends up to and seldom beyond the atlas suggests that tonsillar herniation is designed to protect the cervicomedullary cord from compression by the odontoid process against the bony posterior arch of atlas. The frequent presence of bifid posterior arch of atlas is a protective and natural “decompressive laminectomy.”[13] We speculated that bifid arch of atlas provides an open close door kind of phenomenon wherein the posterior arch opens upon flexion of the head to provide space to the odontoid process intrusion and closes on neck extension when the odontoid process is anteriorly positioned. The bone abnormality of the arch of atlas, lateral disposition of the facets of atlas in relationship with the facets of axis and occipital condyle, reduction of the height of the occipital bone and atlas and axis complex all seem to be protective natural designs instituted to protect the neural structures against potential damage by the abnormal movements of the odontoid process.…”

“…The bone abnormality of the arch of atlas, lateral disposition of the facets of atlas in relationship with the facets of axis and occipital condyle, reduction of the height of the occipital bone and atlas and axis complex all seem to be protective natural designs instituted to protect the neural structures against potential damage by the abnormal movements of the odontoid process. [13] “Short neck,” “short head” in the form of short clivus and posterior fossa bone compartment, torticollis, bone fusions, platybasia, and several other musculoskeletal malformations seem to be an effect of nature's attempt to reduce the length of the neural canal to permit a stretch free traverse of the brainstem and spinal cord. [14]…”