title: Posterior atlanto-axial fixation with polyaxial C1 lateral mass screws and C2 pars screws.
abstract: OBJECTIVE
  C1-C2 instability or painful osteoarthritis are recognised indications for posterior atlanto-axial fixation. In the traditional trans-articular C1-C2 screw fixation, up to 20% of patients cannot have safe placement of bilateral screws in the event of a medially located vertebral artery and a straight screw trajectory in the sagittal plane. The more recently developed C1-C2 fixation technique with individual C1 lateral mass screws and converging C2 pars screws can be employed in case of a medially located vertebral artery and has comparable biomechanical strength. This is a prospective observational study to investigate the advantages, the safety, and the drawbacks of posterior atlanto-axial fixation with polyaxial C1 lateral mass screws and C2 pars screws.
  
  
  METHODS
  Twelve consecutive patients with C1-2 instability (n = 11) and painful osteoarthritis (n = 1) underwent a posterior atlanto-axial fixation with polyaxial C1 lateral mass screws and C2 pars screws. The average follow-up was 16 months and all patients reached the 12-month follow-up.
  
  
  RESULTS
  No hardware failure occurred in any of the patients. Correct screw placement and construct stability was found in all 12 patients (100%) at 6 and 12 months after surgery. Mean neck pain on a visual analogue scale (VAS) was 2.1 at 6 months and 2.0 at 12 months. Only transient complications were observed: one patient presented with progressive intestinal herniation through the iliac crest scar; one suffered from severe pain at the posterior iliac crest for 3 months and three patients complained of annoying pain/dysaesthesia in the C2 dermatome for 3-6 months after surgery.
  
  
  CONCLUSIONS
  This study confirms that posterior atlanto-axial fixation with polyaxial C1 lateral mass screws and C2 pars screws is a safe and effective surgical option in the treatment of atlanto-axial instability or painful osteoarthritis.
authors.affiliation: Neurosurgical Spine Unit, Hirslanden Klinik, Witellikerstrasse 40, 8008, Zürich, Switzerland. mpayer@hotmail.com
authors.forename: M
authors.initials: M
authors.lastname: Payer
authors.forename: M
authors.initials: M
authors.lastname: Luzi
authors.forename: E
authors.initials: E
authors.lastname: Tessitore
mesh_terms: D000328:Adult; D000368:Aged; D001268:Atlanto-Axial Joint / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D001368:Axis, Cervical Vertebra / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D001863:Bone Screws; D001270:Cervical Atlas / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D005260:Female; D050723:Fractures, Bone / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery; D006801:Humans; D004204:Joint Dislocations / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery; D008297:Male; D008875:Middle Aged; D019547:Neck Pain / Q000209:etiology / Q000517:prevention & control / Q000601:surgery; D009809:Odontoid Process / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery; D010003:Osteoarthritis / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery; D011183:Postoperative Complications / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control; D011859:Radiography; D013122:Spinal Diseases / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods; D016896:Treatment Outcome; D055815:Young Adult