title: Subsidence as of 12 months after single-level anterior cervical inter-body fusion. Is it related to clinical outcomes?
abstract: BACKGROUND
  Subsidence is a frequent phenomenon in the interbody fusion process in patients with anterior cervical discectomy and fusion (ACDF). There is little evidence of whether subsidence in the cervical spine has any impact on clinical outcomes.
  
  
  OBJECTIVE
  The purpose of this study is to investigate the correlation of subsidence and clinical outcomes after ACDF and to consider reasons subsidence might not cause unfavorable clinical outcomes.
  
  
  METHODS
  A total of 158 consecutive patients who underwent single-level ACDF were included. The patients were divided into a subsidence group (S-group) and a no subsidence group (N-group), with subsidence defined as a decrease by ≥3 mm in total intervertebral height (TIH). We analyzed outcomes resulting from subsidence, particularly focusing on clinical outcomes and subsequent global and segmental kyphosis using a repeated measure analysis of variance (RM-ANOVA).
  
  
  RESULTS
  Subsidence occurred in 74 patients (46.8%) as of a 12-month follow-up. The S-group included 58.6% with a stand-alone cage for interbody fusion (p = 0.002). Clinical outcomes improved significantly over time (neck pain, RM-ANOVA: F(1.3, 205) = 125.1, p < 0.001; arm pain, RM-ANOVA: F(1.3, 203) = 290.8, p < 0.001). There was no significant difference in interaction with subsidence and clinical outcomes between the S- and N-group (neck pain, RM-ANOVA: F(2,153) = 1.04, p = 0.356, partial η(2) = 0.229; arm pain, RM-ANOVA: F(2,153) = 0.56, p = 0.571, partial η(2) = 0.142). Segmental angle increased in both groups over time and showed a statistically significant difference between the S- and N-groups (RM-ANOVA: F(3,143) = 6.148, p = 0.001, partial η(2) = 0.959). Although, global cervical angle decreased generally and displayed no statically significant difference between the S- and N-group (RM-ANOVA: F(3,119) = 2.361, p = 0.075, partial η(2) = 0.056).
  
  
  CONCLUSIONS
  Radiographic subsidence after ACDF occurred in 46.8% patients as of 12 months after the single-level ACDF. The lack of correlation between bad clinical outcome and radiographic subsidence may be due to segmental kyphosis, preserved posterior height, and maintaining the global cervical angle.
authors.affiliation: Department of Neurosurgery, Konyang University Hospital, Konyang University College of Medicine, Daejeon, South Korea.
authors.forename: Chang-Hyun
authors.initials: CH
authors.lastname: Lee
authors.forename: Ki-Jeong
authors.initials: KJ
authors.lastname: Kim
authors.forename: Seung-Jae
authors.initials: SJ
authors.lastname: Hyun
authors.forename: Jin S
authors.initials: JS
authors.lastname: Yeom
authors.forename: Tae-Ahn
authors.initials: TA
authors.lastname: Jahng
authors.forename: Hyun-Jib
authors.initials: HJ
authors.lastname: Kim
mesh_terms: D000328:Adult; D001860:Bone Plates; D002574:Cervical Vertebrae / Q000601:surgery*; D017586:Diskectomy / Q000379:methods*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007738:Kyphosis / Q000150:complications / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D019547:Neck Pain / Q000209:etiology / Q000601:surgery; D012189:Retrospective Studies; D013123:Spinal Fusion / Q000379:methods*; D016896:Treatment Outcome