The upper cervical angle and intervals are important to the health and function of the brainstem and cord. The brain scan below is from a case study by Drs. Milhorat, Bolognese and Nishikawa published in the Journal of Neurology in December 2007, using a Fonar Upright MRI in evaluating excess motion in the upper cervical spine.
This particular case was affected by an inherited disorder of connective tissue called Ehler’s-Danlos. Among other things, Ehler’s-Danlos is associated with loose ligaments predisposing joints to strains, subluxations and dislocations. The excess motion in the upper cervical spine can cause neurological signs and symptoms.
The upper cervical angle, technically known as the clivoaxial angle, is determined by drawing a line along the base of the skull (clivus) and a second line down the backside of the body of the second cervical vertebra (axis) and measuring the degrees of separation between them. The angle is noted as CXA on the brain scan below and should be approximately 140 degrees.
The intervals are critical spaces that separate the base of the skull from the upper cervical spine, as well as spaces between the atlas (C1) and axis (C2) vertebrae of the upper cervical spine. The two spaces in the brain scan are denoted as BDI and BAI and will be explained further below.
The atlas vertebra (C1) of the upper cervical spine connects to the condyles of the posterior fossa of the base of the skull. The front border of the posterior fossa is called the clivus portion of the base of the skull. It is represented by line C in the brain scan above. The brainstem lies parallel to the clivus. (The following link is to a page on this site that discusses the design and angles of the posterior fossa).
The pitch of the clivus varies in different races and in different individuals. In certain cases its pitch is too flat, platybasia, which predisposes the brain to a Chiari malformation when the head is tilted forward. A Chiari malformation occurs when the bottom of the brain comes in contact with the base of the cranial vault.
In addition to the angle of the base of the skull and the pitch of the clivus, the angle of the clivus relative to the upper cervical spine, clivoaxial angle (CXA) mentioned above and shown in the brain scan above, is also important. The pitch of the upper cervical spine is represented by line D drawndown the backside of the odontoid process of the axis or second cervical vertebra (C2). The odontoid, also known as the dens, is the upward pointing tooth-like projection as seen in the sketch below of the axis (C2).
In contrast to the clivoaxial angle, the upper cervical intervals are several specific spaces between certain points of the base of the skull and upper cervical spine, and between the upper cervical vertebrae atlas (C1) and axis (C2).