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Atlantoaxial Rotatory Fixation (Subluxation)

- See: Atlanto-axial Subluxation:

- Discussion:
     - a condition in which there is fixed rotation of C1 on C2;
     - fixation may occur with in the range of normal rotation, may occur w/subluxation, or may occur w/ dislocation;
     - clinically patients will have ipsilateral rotation and contralateral tilt of the head in relation to the lateral mass of C1;
           - the contra-lateral sternocleidomastoid may be spastic;
     - rotatory fixation may arise from neglected cases of torticollis;
     - often, the diagnosis is delayed by several months upto 1 year;
     - key feature is that when head is rotated maximally to opposite side, the malaligned relationship of C1 to C2 appears unchanged;
     - pertinent anatomy:
           - anatomically, if the patient's head is turned to the right, then the right lateral mass of C1 is rotated posteriorly;
           - if transverse ligament is intact, only a severe amount of rotation can result in facet dislocation and subsequent narrowing of the SAC;
           - if transverse ligament has ruptured, 5 mm of anterolithesis and 45 deg of rotation will narrow the SAC to less than 12 mm;
                   - vertebral arteries are also at risk in this situation;

- Diff Dx:
     - Atlantoaxial Subluxation
     - Grissel's Syndrome
     - Torticollis
          - will demonstrate spasm or fibrosis of the ipsilateral side, in contrast to rotatory fixation which has spasm on contralateral side;

- Radiographs for Rotatory Fixation:

CT scan:
    - dynamic CT scan is test of choice;
    - CT is first taken with the head in its rotated position (injured position), and subsequently, the CT scan is taken with the head is rotated 
           maximally to the opposite side;
           - in rotatory fixation, the relationship between C1 and C2 is unchanged;

- Classification:
      - Type I: (most common)
           - rotary fixation is w/in the normal ROM and has no anterior displacement (ie, ADI is normal);
           - transverse ligament is intact and odontoid process acts as pivot;
           - treated w/ soft collar and analgesics +/- halter traction;
      - Type II:
           - rotatory fixation w/ anterior displacement of 3 to 5 mm, w/ disruption of the transverse ligament;
           - one lateral mass is displaced where as the remaining mass is intact and acts as a pivot;
      - Type III:
           - rotatory fixation w/ anterior displacement of more than 5 mm, which implies disruption of both the transverse and alar ligaments;
          - both lateral masses are displaced;
      - Type IV:
           - rotatory fixation with posterior displacement;

- Treatment:
      - pt requires special attention when any degree of anterior displacement is present;
      - typically patients are placed in cervical halter traction in acute cases;
      - w/ chronic fixation, it is first necessary to determine whether concomitant atlanto-occipital subluxation is present;
            - if not present, then procede w/ antanto-axial fusion;
            - if atlanto-occipital subluxation is present, then consider fusion from occiput to C2

The management of rotatory atlanto-axial subluxation in children.

Atlanto-axial rotatory fixation. (Fixed rotatory subluxation of the atlanto-axial joint).