title: Unilateral C1 Lateral Mass and C2 Pedicle Screw Fixation for Atlantoaxial Instability in Rheumatoid Arthritis Patients: Comparison with the Bilateral Method.
abstract: OBJECTIVE
  Bilateral C1 lateral mass and C2 pedicle screw fixation (C1LM-C2P) is an ideal technique for correcting atlantoaxial instability (AAI). However, the inevitable situation of vertebral artery injury or unfavorable bone structure may necessitate the use of unilateral C1LM-C2P. This study compares the fusion rates of the C1 lateral mass and C2 pedicle screw in the unilateral and bilateral methods.
  
  
  METHODS
  Over five years, C1LM-C2P was performed in 25 patients with AAI in our institute. Preoperative studies including cervical X-ray, three-dimensional computed tomography (CT), CT angiogram, and magnetic resonance imaging were performed. To evaluate bony fusion, measurements of the atlanto-dental interval (ADI) and CT scans were performed in the preoperative period, immediate postoperative period, and postoperatively at 1, 3, 6, and 12 months.
  
  
  RESULTS
  Unilateral C1LM-C2P was performed in 11 patients (44%). The need to perform unilateral C1LM-C2P was due to anomalous course of the vertebral artery in eight patients (73%) and severe degenerative arthritis in three patients (27%). The mean ADI in the bilateral group was 2.09 mm in the immediate postoperative period and 1.75 mm in 12-months postoperatively. The mean ADI in the unilateral group was 1.82 mm in the immediate postoperative period and 1.91 mm in 12-months postoperatively. Comparison of ADI measurements showed no significant differences in either group (p=0.893), and the fusion rate was 100% in both groups.
  
  
  CONCLUSIONS
  Although bilateral C1LM-C2P is effective for AAI from a biomechanical perspective, unilateral screw fixation is a useful alternative in patients with anatomical variations.
authors.affiliation: Department of Neurosurgery, Hanyang University Medical Center, Seoul, Korea.
authors.forename: Seung-Chull
authors.initials: SC
authors.lastname: Paik
authors.affiliation: Department of Neurosurgery, Hanyang University Medical Center, Seoul, Korea.
authors.forename: Hyoung-Joon
authors.initials: HJ
authors.lastname: Chun
authors.affiliation: Department of Neurosurgery, Hanyang University Medical Center, Seoul, Korea.
authors.forename: Koang Hum
authors.initials: KH
authors.lastname: Bak
authors.affiliation: Department of Neurosurgery, Guri Hanyang Hospital, Guri, Korea.
authors.forename: Jeil
authors.initials: J
authors.lastname: Ryu
authors.affiliation: Department of Neurosurgery, Guri Hanyang Hospital, Guri, Korea.
authors.forename: Kyu-Sun
authors.initials: KS
authors.lastname: Choi
keywords: Atlantoaxial; Bilateral; C1-2; Harm's Technique; Instability; Unilateral