title: Inadvertent C2-C3 union after C1-C2 posterior fusion in adults.
abstract: BACKGROUND
  Some authors pointed out that there were more than a few patients with inadvertent C2-C3 union after C1-C2 posterior fusion, although few detailed studies of C2-C3 union have been reported. The purpose of this study was to clarify whether C2-C3 union accelerated adjacent C3-C4 disc degeneration after C1-C2 posterior fusion and to investigate the related factors for C2-C3 union.
  
  
  METHODS
  Sixteen patients with rheumatoid arthritis (RA group) (4 males, 12 females, mean age 60 years, mean follow-up period 4 years and 3 months) and fifteen patients without RA (non-RA group) (11 males, 4 females, mean 52 years, mean follow-up period 3 years and 10 months) who underwent C1-C2 posterior fusion were radiologically assessed. The C2-C3 union was defined as trabecular bone formation at C2-C3 interlamina in lateral radiograph. C3-C4 disc height was measured to evaluate the disc degeneration.
  
  
  RESULTS
  C2-C3 union rate was 56% and 60% in RA group and non-RA group, respectively. In RA group, postoperative C3-C4 disc height was lower (Student's t-test, P = 0.029) and the decrease rate of C3-C4 disc height was higher (Student's t-test, P = 0.015) in patients with C2-C3 union than in patients without C2-C3 union. In non-RA group, the age at operation was older (Student's t-test, P = 0.0007), and the C1-C2 fusion angle (Student's t-test, P = 0.012) was smaller in patients with C2-C3 union than in patients without C2-C3 union.
  
  
  CONCLUSIONS
  C2-C3 union after C1-C2 posterior fusion occurred in more than half of both groups. Inadvertent C2-C3 union should be considered a radiological complication and a potential risk factor due to acceleration of C3-C4 disc degeneration in RA.
authors.affiliation: Department of Orthopaedic Surgery, Hirosaki University School of Medicine, Hirosaki, Aomori 036-8562, Japan. naritake03@ybb.ne.jp
authors.forename: Kazunari
authors.initials: K
authors.lastname: Takeuchi
authors.forename: Toru
authors.initials: T
authors.lastname: Yokoyama
authors.forename: Shuichi
authors.initials: S
authors.lastname: Aburakawa
authors.forename: Kazumasa
authors.initials: K
authors.lastname: Ueyama
authors.forename: Junji
authors.initials: J
authors.lastname: Ito
authors.forename: Akio
authors.initials: A
authors.lastname: Sannohe
authors.forename: Akihiro
authors.initials: A
authors.lastname: Okada
authors.forename: Satoshi
authors.initials: S
authors.lastname: Toh
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001172:Arthritis, Rheumatoid / Q000601:surgery; D001268:Atlanto-Axial Joint / Q000473:pathology / Q000601:surgery*; D002574:Cervical Vertebrae / Q000473:pathology* / Q000601:surgery*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D013123:Spinal Fusion / Q000009:adverse effects*