Introduction: Preoperative parameters including the T1 slope (T1S) and C2-7 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.
Methods: 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), C2-7 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.
Results: 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.
Conclusions: A lower T1S (T1S <28°) is 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.
Patient Care: This study demonstrated the effect of T1 slope on ACDF, which has not yet been studied. Especially, the risk of subsidence is high in patients with low T1 slope.
Learning Objectives: By conclusion of this session, participants should be able to: 1)identify an efforts to reduce subsidence in patients with low T1S should be taken. To reduce subsidence, a plate that disperses the loading on the cage may be applied; a more careful endplate preparation or lower-elasticity graft such as an allograft application may also be considered, 2)identify the effect of indirect decompression by the cage insertion will be decreased due to high degrees of subsidence. Thus, we should consider sufficient direct decompression to prevent symptom recurrence according to subsidence in low TIS patients.