Canis ISSN: 2398-2942

Atlantoaxial joint: subluxation

Synonym(s): Atlantoaxial joint instability, atlantoaxial malformation

Contributor(s): Rodney Bagley, Harry Scott


  • Atlantoaxial instability occurs in numerous, usually small but occasionally large, dog breeds.
  • Acute or insidious onset neck pain and tetraparesis in young animals particularly of toy breeds.
  • Signs: classically upper motor neuron (UMN) signs in thoracic and pelvic limbs.
  • Diagnosis: signs, radiography.
  • Treatment: surgical stabilization.
  • Prognosis: guarded.



  • Absence of dens.
  • Fracture of odontoid process.
  • Malformed odontoid process.
  • Ruptured ligaments - traumatic rupture or malformation of the transverse atlantal ligament.

Predisposing factors

  • Congenital abnormality predisposes to subluxation as a result of minor trauma.


  • Malformation, malarticulation of the atlantoaxial joint.
  • May be caused by abnormal ligamentous formation in this area, or abnormal formation of the dens.
  • In some cases, the dens is misdirected dorsally into the spinal cord.
  • Dorsal displacement of axis → compression of cervical spinal cord → neurological signs.
  • In normal animal atlantoaxial joint is stabilized by transverse, apical and alar ligaments.
  • Rupture or damage to these structures or the dens predisposes to subluxation.
  • Most cases present as a result of a traumatic incident superimposed on congenital anomaly.


  • Usually slow progressive onset as animal matures.
  • May be acute tetraparesis.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Schulz K S, Waldron D R & Fahie M (1997) Application of ventral pins and polymethylmethacrylate for the management of atlantoaxial instability - results in nine dogs. Vet Surg 26 (4), 317-325 PubMed.
  • Jeffery N D (1996) Dorsal cross pinning of the atlantoaxial joint - new surgical technique for atlantoaxial subluxation. JSAP 37 (1), 26-29 PubMed.
  • Tomlinson J (1996) Surgical conditions of the cervical spine. Semin Vet Med Surg (Small Anim) 11 (4), 225-234 PubMed.
  • McCarthy R J, Lewis D D & Hosgood G (1995) Atlantoaxial subluxation in dogs. Comp Cont Ed Pract Vet 17 (2), 215-226 VetMedResource.
  • Thomas W B et al (1991) Surgical management of atlantoaxial subluxation in 23 dogs. Vet Surg 20 (6), 409-412 PubMed.
  • Fingeroth, J M, Smeak, D D (1989) Laminotomy of the axis for surgical access to the cervical spinal cord - A case report. Vet Surg 18 (2), 123-129 PubMed.
  • Denny H R et al (1988) Atlantoaxial sublucation in the dog - a review of 30 cases and an evaluation of treatment by lag screw fixation. JSAP 29 (1), 37-47 Wiley Online Library.

Other sources of information

  • Shores A (1992)Spinal trauma - pathophysiology and management of traumatic spinal injuries.Vet Clin North Am Small Anim Pract22(4), 859-888. (Review.)
  • Sorjonen D C et al (1980)Atlatoaxial instability - a ventral surgical technique for decompression, fixation and fusion.15th ACVS meeting, Knoxville, Tennessee.