If this is a fixed defect, C2 is rotated in conjunction with C1. The head may be pointed anteriorly, C1 is turned. On CT, C1 is not oriented in line with the head. type II: the atlas is rotated on one lateral articular process with 3 to 5 mm of anterior displacement. In a vertical subluxation, the dens is often above the McGregor line by over 8 mm in men and 9.7 mm in women. rotatory subluxation, known as atlantoaxial rotatory fixation (AARF) is characterized into four different types according to the Fielding and Hawkins classification 3 : type I: the atlas is rotated on the odontoid with no anterior displacement. Neck stiffness, Atlanto-axial instability, Cranio. The expected distance between the anterior arch of C1 and the dens in the fully flexed position should be <3 mm in an adult (~5 mm in a child) 5.Īlso, the anterior translocation of the atlas causes the posterior arch of C1 to become anterior to the spinolaminar line 7. KEY WORDS: Elongated odontoid process, Crowned dens syndrome, Calcification, Apical ligament, Alar ligament. In a non-traumatic setting, flexion and extension views may be performed. Type IV: rotation and posterior displacement of the atlas 1 In the elderly population, this fracture type represents the most common cervical spine fracture and in the population older than 80 years, the most common spine fracture of all. Type III: comprises rotation of the atlas on both lateral articular processes with anterior displacement greater than 5 mm Odontoid fractures are widely common and reported to account for up to 15 of all cervical spine injuries. The condition where the dens is separated from the body of the axis is called os odontoideumand may cause nerve and circulation compression syndrome. The dens exhibits a slight constriction where it joins the main body of the vertebra. Type II: the atlas is rotated on one lateral articular process with 3 to 5 mm of anterior displacement The dens, also called the odontoid process or the peg, is the most pronounced projecting feature of the axis. Type I: the atlas is rotated on the odontoid with no anterior displacement Rotatory subluxation, known as atlantoaxial rotatory fixation (AARF) is characterized into four different types according to the Fielding and Hawkins classification 3: There are several ways in which a subluxation can occur: Retropharyngeal abscess / Grisel syndrome It exhibits a slight constriction or neck, where it joins the main body of the vertebra. Atlanto-axial subluxations are often associated with high energy traumas, with higher occurrence among children and young adults 6. The odontoid process (also dens or odontoid peg) is a protuberance (process or projection) of the Axis (second cervical vertebra).
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