- Lateral View:
- key element is whether there is anterolithesis, since this will dramatically
narrow the
SAC w/ any degree of rotation;
-
ADI:
- it may be difficult to measure the ADI due to lateral mass rotation;
- in children upto 3.5 mm may be normal;
- ADI: 3.5 to 5 mm,
transverse ligament is insufficient; (this is a type II injury);
- ADI: > 5 mm:
- indicates failure of the alar ligaments;
- consistent w/ type III rotatory subluxation;
- Open Mouth View:
- dens is laterally displaced towards one side w/ asymmetry of lateral masses;
- ie, the dens is closer to one lateral mass than the other;
- one lateral mass is rotated anteriorly, appearing wider and rotated toward midline;
- the opposite lateral mass, appears father from midline;
- joint space of lateral mass rotated posteriorly appears to be overlapping
the one below;
- position of C2 spinous process:
- in rotaroy fixation, the patient's chin and spinous process will be on the same side
of the midline and the C2 spinous process tilts toward the side of facet displacement;
- Radiographic Differential Dx:
- asymmetry of the lateral masses can be a normal finding if the patient's
head is turned while the radiograph is being taken;
- w/ rotatory fixation, however, attempts to gently rotate the head to
the opposite side will not change the asymmetric relationship
of the dens to the lateral masses;
-
torticollis
- note that a right sided torticollic tilt, will cause a left sided shift of the lateral
mass and spinous process;
- in contrast, rotatory fixation involves ipsilateral rotation and contralateral tilt;
- anatomically, if the patient's head is turned to the right, then the
right lateral mass is rotated posteriorly;
- finally, unlike rotatory fixation, true torticollis will show reversal
of the rotation of C1 on C2, as the head is turn to the opposite side;
- Flouroscopy
- cineroentogenograms are most useful to demonstrate the fixed relationship
of the atlas to lateral masses as the head is turned to the opposite side;
- CT scan:
- obtain thin section CT thru upper C spine inorder to evaluate eccentric
position of dens & rotation of the
atlas w/ respect to the
axis;
- failure of C1 to reposition on a left and right rotation CT scan indicates a fixed deformity;
- turn neck in contralateral direction as far as voluntarily possible;
those with transient
torticollis will show a reduction or reversal of the
rotation of C1 on C2, while those with atlantoaxial fixation will not;
- lateral masses of C1 are displaced
- one anteriorly and the other posteriorly w/ respect to C2;
-
ref:
-
Dynamic computerized tomography of the occiput-atlas-axis complex
in trauma patients with odontoid lateral mass asymmetry.
-
Atlanto-axial instability and spinal cord compression in children--diagnosis by
computerized tomography.
- Kowalski HM, Cohen WA, Cooper P, et al: Pitfalls in the CT diagnosis of
atlanto-axial rotatory subluxation.
AJR 1987;149:595-600.
Klein DM, Kuhn JP: Problems in the radiographic diagnosis of
atlanto-axial rotation deformity.
Conc Pediatr Neurosurg 1985;5:26-33.
