Short Segment Rigid Fixation for a Patient of Basilar Invagination and Assimilated C1 with Quadriperesis

Atlanto-occipital non-segmentation failure of segmentation between the fourth occipital sclerotome and the first cervical sclerotome results in atlanto-occipital non-segmentation/ assimilation, also known as occipitalization of the atlas.1The incidence of occipitalisation has been reported to be between 0.08% to 3% of the general population, affecting males and females equally.2 A cartilaginous cleft and an open synchondrosis between the osseous posterior arches of the atlas is a normal finding in children up to four years of age; therefore, a true defect in the posterior arch was diagnosed only in patients who were more than four years old.3 Atlanto-occipital fusion reduces the foramen magnum dimension leading to neurological complications due to compression of spinal cord.4 The slow development of the fibrosis was the source of gradual spinal-cord compression with increasing symptoms.5 Fusion of atlanto-occipital joints can also result in restricted neck movement.6 Basilar invagination is an abnormality at the craniocervical junction (CVJ) either congenital or degenerative, where the odontoid tip is inside the foramen magnum with or without neurological symptoms.7