This study was to indentify the change of sagittal cervical alignment and balance after 3-level anterior cervical discectomy and fusion (ACDF) and to determine the threshold of T1 slope minus C2-C7 cervical lordosis (T1S-CL) in 3-level ACDF.

A single-center, retrospective, case-series study was conducted. A total of 73 cases with cervical spondylotic myelopathy (CSM) were collected from deportment of spinal surgery, Peking University People's Hospital including with a mean follow-up of 73.8±8.6 (m), where 45 patients was performed 3-level ACDF with stand-alone self-locked cage system and 28 cases with anterior cage-with-plate system. The cervical sagittal alignment paramters included CL, C2-C7 sagittal vertical axis (C2-C7 SVA), T1S and T1S-CL (the measurement for evaluating cervical balance), which were measured on cervical X-ray at baseline and final follow-up. The quality-of-life scale was evaluated by Neck disability index (NDI) and Japanese Orthopedic Association (JOA) score, where NDI with 20 was defined as the threshold of quality-of-life scale. The threshold of T1S-CL was determined according to radiological and clinical outcomes by both linear and logistic regression model.

The CL and T1S improved (P＜0.05) and T1S-CL decreased by 4.5±9.7 (P=0.008) at last while C2-C7 SVA was of no significance compared to baseline (P=0.253). For clinical outcomes, all cases acquired inprovement on NDI and JOA (P＜0.001). At last, C2-C7 SVA was correlated to T1S-CL and T1S-CL was correlated to T1S. There were close correlation between cervical radiological parameters and NDI. C2-C7 SVA was independent risk factor for NDI (χ²=34.02, P=0.001, odd ratio=1.51, ROC-AUC=0.955) and T1S-CL was independent influencing factor for C2-C7 SVA (χ²=12.26, P=0.001, odd ratio=1.24, ROC-AUC=0.878). The two regression models predicted C2-C7 SVA with a cutoff of 29.2 mm when NDI was 20, corresponded to the threshold on T1S-CL of 20.7°.

Consective 3-level ACDF was able to rebuilting cervical alignment and balance status. The cutoff on C2-C7 SVA with 29.2 mm corresponds to a thershold of T1S-CL with 20.7° in multilevel ACDF.