T1 slope minus cervical lordosis in multilevel anterior cervical discectomy and fusion with or without plate: a mean 6-year follow up

Purpose: Cervical alignment between self-locked cage (SLC) and anterior cage-with-plate (ACP) system was debatable, especially in multilevel anterior cervical discectomy and fusion (ACDF). T1 slope minus C2-C7 cervical lordosis (T1S-CL) was critical for cervical-balance while without identified threshold. Thus the study was to compare sagittal alignment between SLC and ACP on 3-level ACDF and to identify the threshold of T1S-CL in 3-level ACDF. Methods 45 patients of 3-level SLC and 28 cases of 3-level ACP with well-matched demographics were retrospectively enrolled with 6.1-year follow-up. Cervical alignment paramters were CL, C2-C7 sagittal vertical axis (C2-C7 SVA), T1S and T1S-CL, as well as adjacent segment degeneration (ASD), obtained on X-ray. Neck disability index (NDI) and Japanese Orthopedic Association (JOA) score were recorded for evaluating quality of life (QOL). NDI of 20 was difined as the cutoff of QOL. Threshold of T1S-CL was determined by both linear and logistic regression model. Result CL, C2-C7 SVA and T1S were insignificant at baseline and all parameters were indifferent at last (P ˃0.05). CL and T1S improved at last in both groups (P < 0.05). The incidence of ASD was comparable between groups (P ˃0.05). Both groups acquired inprovement on NDI and JOA (P < 0.001). There were close correlation among alignment paramters and between parameters and NDI at final follow-up. C2-C7 SVA was independent risk factor for NDI and two regression models predicted C2-C7 SVA with a cutoff of 29.2 mm, corresponded to the threshold on T1S-CL of 20.7°. Conclusions It is comparable on alignment reconstruction between SLC and ACP system. The cutoff on C2-C7 SVA with 29.2 mm corresponds to a thershold of T1S-CL with 20.7° in multilevel ACDF.