If this is a fixed defect, C2 is rotated in conjunction with C1. The odontoid process fracture (also known as the peg or dens fracture) occurs where there is a fracture through the odontoid process of C2. The head may be pointed anteriorly, C1 is turned. The crowned dens syndrome is an acute presentation due to crystal deposition in the periodontoid soft tissues, and should not be used for chronic retro-odontoid pseudotumor (also caused by CPPD).As such the term should not be used unless inflammatory symptoms and pain are present 4. On CT, C1 is not oriented in line with the head. In a vertical subluxation, the dens is often above the McGregor line by over 8 mm in men and 9.7 mm in women. 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. The craniovertebral joint between the atlas and the axis is called, the atlanto-axial joint. (The skull sits on top of the atlas. (The axis is the 2nd highest spinal bone.) The atlas is the first bone of your neck it sits on top of the axis. The C1 vertebra, carrying the cranium, rotates on this. The odontoid process, also known as the dens, is an upward projectile of bone that arises from the front part of the center of the axis vertebra. In a non-traumatic setting, flexion and extension views may be performed. The odontoid process lies anterior to the spinal cord and is used as the pivot for the rotation of the head. Type IV: rotation and posterior displacement of the atlas Type III: comprises rotation of the atlas on both lateral articular processes with anterior displacement greater than 5 mm 10 11 12 Type II fractures are the most common odontoid fracture and the only type normally associated with atlantoaxial dislocation. Type II: the atlas is rotated on one lateral articular process with 3 to 5 mm of anterior displacement Type II odontoid fractures occur at the base between the transverse ligament and body of C2 body. 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: 28.6 and 28.7), located between the odontoid process and the body, begins to close around age 3 to 6 years of age and usually fuses around 11 to 12 years of. Retropharyngeal abscess / Grisel syndrome Atlanto-axial subluxations are often associated with high energy traumas, with higher occurrence among children and young adults 6.
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