J Korean Neurosurg Soc.  2017 Sep;60(5):567-576. 10.3340/jkns.2017.0404.001.

A Lower T1 Slope as a Predictor of Subsidence in Anterior Cervical Discectomy and Fusion with Stand-Alone Cages

  • 1Department of Neurosurgery, Pusan National University Yangsan Hospital, Yangsan, Korea. md6576@naver.com
  • 2Research Institute for Convergence of Biomedical Science and Technology, Pusan National University Yangsan Hospital, Yangsan, Korea.
  • 3Department of Neurosurgery, Pusan National University School of Medicine, Yangsan, Korea.


Preoperative parameters including the T1 slope (T1S) and C2-C7 sagittal vertical axis (SVA) have been recognized as predictors of kyphosis after laminoplasty, which is accompanied by posterior neck muscle damage. The importance of preoperative parameters has been under-estimated in anterior cervical discectomy and fusion (ACDF) because there is no posterior neck muscle damage. We aimed to determine whether postoperative subsidence and pseudarthrosis could be predicted according to specific parameters on preoperative plain radiographs.
We retrospectively analyzed 41 consecutive patients (male: female, 22: 19; mean age, 51.15±9.25 years) who underwent ACDF with a stand-alone polyether-ether-ketone (PEEK) cage (>1 year follow-up). Parameters including SVA, T1S, segmental angle and range of motion (ROM), C2-C7 cervical angle and ROM, and segmental inter-spinous distance were measured on preoperative plain radiographs. Risk factors of subsidence and pseudarthrosis were determined using multivariate logistic regression.
Fifty-five segments (27 single-segment and 14 two-segment fusions) were included. The subsidence and pseudarthrosis rates based on the number of segments were 36.4% and 29.1%, respectively. Demographic data and fusion level were unrelated to subsidence. A greater T1S was associated with a lower risk of subsidence (p=0.017, odds ratio=0.206). A cutoff value of T1S<28° significantly predicted subsidence (sensitivity: 70%, specificity: 68.6%). There were no preoperative predictors of pseudarthrosis except old age.
A lower T1S (T1S<28°) could be a risk factor of subsidence following ACDF. Surgeons need to be aware of this risk factor and should consider various supportive procedures to reduce the subsidence rates for such cases.


Cervical vertebrae; Postural balance; Spinal fusion; Prosthesis failure; Risk assessment

MeSH Terms

Cervical Vertebrae
Logistic Models
Neck Muscles
Postural Balance
Prosthesis Failure
Range of Motion, Articular
Retrospective Studies
Risk Assessment
Risk Factors
Sensitivity and Specificity
Spinal Fusion


  • Fig. 1 Flow diagram depicting the patient inclusion process. ACDF: anterior cervical discectomy and fusion, ACDFP: ACDF with anterior plating, TDR: total disc replacement, PEEK: polyether-ether-ketone.

  • Fig. 2 Measurements of the radiological parameters. A: Neutral lateral image. B: Flexion lateral image, flex: flexion; inter-spinous: inter-spinous distance. C: Extension lateral image. T1SCA: T1S minus CA, SA: segmental angle, CA: C2–C7 cervical angle, TIH: total intervertebral height, SVA: sagittal vertical axis.

  • Fig. 3 Correlations among preoperative parameters. The width of the arrow represents the correlation coefficient R. SVA: sagittal vertical axis, T1S: T1 slope, CA: C2–7 cervical angle, ROM: range of motion, SA: segmental angle, T1SCA: T1 slope minus C2–7 cervical angle.

  • Fig. 4 Effect of T1 slope on cervical alignment. *Significant group difference at each time point (p<0.05), †Significant group difference in the longitudinal trend (p<0.05). TIH: total intervertebral height, T1S: T1 slope, CA: C2-7 cervical angle, SA: segmental angle.

  • Fig. 5 Scheme illustrating the statistical analysis. F: force, θ: T1 slope, α: the angle between spinous process and F sin θ, Fdisc: loading on disc.

Cited by  1 articles

Risk Factors of Allogenous Bone Graft Collapse in Two-Level Anterior Cervical Discectomy and Fusion
Joon-Bum Woo, Dong-Wuk Son, Su-Hun Lee, Jun-Seok Lee, Sang Weon Lee, Geun Sung Song
J Korean Neurosurg Soc. 2019;62(4):450-457.    doi: 10.3340/jkns.2019.0008.



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