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Pseudosubluxation of the C spine


- Discussion:
    - pediatric pseudosubluxation refers to normal mobility of C-2 on C-3 in flexion which may be so pronounced as to be mistaken
           for pathologic motion; (is normal in children < 8 years old);
    - prevalence:
           - pseudosubluxation may be seen in 40% of children at C2-C3 level and in 14% of children at the C3-C4 level
    - etiology:
           - pediatric C-spine (up to 8 yrs of age) has greatly increased physiologic mobility as compared to the adult;
           - occurs because of increased ligamentous laxity, more horizontal nature of facet joint (30 deg vs. 60-70 deg in adult);
           - in children, fulcurm of motion that is relatively greatest at C2-C3 level (compared w/ C5-C6 in the adult);
           - 70% of C-spine frx in infants and children occur from C1 to C3;
           - hence increase frequency of atlantoaxial rotatory subluxation as compared to the adult;
           - in normal circumstances, this anterior displacement only occurs in flexion, and should not occur in extension;

- Radiographs:
    - look for anterior displacement of C2 on C3 of up to 4 mm or 40% displacement;
    - often the pediatric cross table lateral will be taken with the child's neck slightly flexed, (because the child's relatively larger head size lies 
          flexed on the trauma board), which accentuates the deformity;
    - absence of significant soft tissue swelling;

- Distinguish between Normal and Abnormal Radiographs:
    - lack of anterior swelling cont alignment of posterior interspinous distances & posterior cervical line (Schwisk) on radiographs
          - note that a crying child may have increase soft tissue density;
    - extension:
          - in normal circumstances, this anterior displacement only occurs in flexion, and should not occur in extension;
          - reduction of subluxation with neck extension help to differentiate this from more serious disorders;
    - Swischuk' Line:
          - line is drawn from the anterior aspect of C1-C3 spinous processes;
          - this line should be within 2 mm of the anterior C2 spinous process;
    - spinal-laminar line:
          - normally should remain intact;
          - straight-line relationship of spinal-laminar line of C-1, C-2, & C-3 in flexion is helpful in differentiating physiologic from pathologic 
                 anterior displacement of C-2 and C-3.
    - flexion:
          - in flexion, posterior arch of C-2 will lie on or behind straight line connecting posterior arches of C-1 & C-3 in nl immature spine;

- Exam:
    - rapid resolution of pain, relatively minor trauma

Pseudosubluxation and other normal variations in the cervical spine in children. A study in one hundred and sixty children.

Anterior displacement of C2 in children: physiologic or pathologic.