Atlantoaxial Instability/Subluxation
A form of spinal anomaly that often results in an abnormal articulation between C1 and C2 vertebrae. This may be acquired as the result of exogenous trauma with either fracture of the occiput, axis, atlas, or disruption of the atlantooccipital ligaments. More commonly there is a congenital abnormality of this vertebral articulation. Various combinations of ligamentous and joint capsule abnormalities may be present. The ventral, cranial aspect of C2 including the dens (odontoid process) which forms the caudal articulation of this joint is also commonly malformed. Atlantoaxial instability may also be associated with abnormally shaped or absent dens. In some instances, there is a fracture of the dens. In still other cases, the dens is present but abnormally angulated in a dorsal direction to compress the spinal cord. Many of these ligamentous and bony abnormalities are assumed to affect the stability of C1 and C2 articulation or result in direct spinal cord compression.
Age of Onset: Variable, commonly less than 1 year old
Sex Predisposition: Any sex of animal can be affected
Clinical Course:
Variable - both acute and insidious onset of neurologic signs have been reported.
Variable - both acute and insidious onset of neurologic signs have been reported.
Clinical Signs:
Posture and Appearance
Cervical ventroflexion
Movement
Ataxia
Varying degress of paresis to paralysis
Intermittent collapse
Proprioception
Proprioceptove deficits in affected limbs
Special Functions (e.g. respiration; urination)
Respiratory paralysis if spinal cord compression is severe
Painful Reactions
Pain on palpation of the cervical vertebral column
Posture and Appearance
Cervical ventroflexion
Movement
Ataxia
Varying degress of paresis to paralysis
Intermittent collapse
Proprioception
Proprioceptove deficits in affected limbs
Special Functions (e.g. respiration; urination)
Respiratory paralysis if spinal cord compression is severe
Painful Reactions
Pain on palpation of the cervical vertebral column
Cervical vertebral column/spinal cord: C1-C2
Unknown
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