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The distances between the dens and surrounding structures are also key features that can suggest the diagnosis, with the normal distance between the dens and basion (i.e., dens–basion interval; BDI) measuring less than 9 mm on CT, and the distance between the atlas and dens (i.e., atlas–dens interval; ADI) measuring less than 3 mm on CT, although this can be increased in cases of ...
Craniocervical instability is more common in people with a connective tissue disease, including Ehlers-Danlos syndromes, [1] osteogenesis imperfecta, and rheumatoid arthritis. [2] It is frequently co-morbid with atlanto-axial joint instability, Chiari malformation , [ 3 ] or tethered spinal cord syndrome .
Atlantoaxial instability is a common asymptomatic finding in rheumatoid arthritis patients. [3] However, it can lead to cervical myelopathy . [ 4 ] Patients with atlantoaxial instability can experience neck pain and headaches in the back of the head (occipital headaches).
Surgery may be used to fix the joint and any associated bone fractures. [1] Neck movement may be reduced long after this injury. [1] Such injuries may also lead to hypermobility, which may be diagnosed with radiographs. [2] This is especially true if traction is used during treatment. [2]
The median atlanto-axial joint is sometimes considered a triple joint: [3] one between the posterior surface of the anterior arch of atlas and the front of the odontoid process; one between the anterior surface of the ligament and the back of the odontoid process; The lateral atlantoaxial joint involves the lateral mass of atlas and axis. [4]
The cruciate ligament of the atlas (cruciform ligament) is a cross-shaped (thus the name) ligament in the neck forming part of the atlanto-axial joint. It consists of the transverse ligament of atlas, a superior longitudinal band, and an inferior longitudinal band. The cruciate ligament of the atlas prevents abnormal movement of the atlanto ...
Excessive laxity of the posterior transverse ligament can lead to atlantoaxial instability, a common complication in patients with Down Syndrome and Ehlers–Danlos syndrome. Laxity has also been hypothesized as the cause of degenerative hypertrophy and mechanical atlantoaxial stress. [ 3 ]
At either lateral extremity, [3]: 426, 430 the membrane is pierced by the vertebral artery [3]: 426, 430, 452 and cervical spinal nerve C1. [ 3 ] : 426 The free border of the membrane arches over the artery and nerve, [ 5 ] and is sometimes ossified (converting the passage for the vertebral artery into a foramen).