The aim of the studywas to examine the effect of cervical segment mobility on spinal sagittal balance parameters after cervical total disc arthroplasty (CTDA) and anterior cervical discectomy and fusion (ACDF) using the first domestic intervertebral disc endoprosthesis.Materials and MethodsThe randomized prospective study included 98 patients (48 with CTDA, 50 with ACDF). Implants used: intervertebral disc endoprosthesis or intervertebral fusion cage (Endocarbon; NPP “MedInzh”, Russia).Total cervical mobility and range of motion in the target and adjacent vertebral motion segments were studied by functional radiography before surgery, at an early postoperative period (within 3 days), and 3, 6, and 12 months after the intervention.Values of cervical lordosis (CL, °), cervical sagittal vertical alignment (cSVA, mm), and first thoracic vertebra slope (T1 slope, °) were determined by using spinal radiography. Surgimap V2.2 software (Nemaris, USA) was used for measurements.ResultsWhen comparing changes of overall cervical mobility at different time intervals, statistically significant differences were obtained in ACDF group (p=0.001). When comparing this parameter between ACDF and CTDA, a statistically significant difference was found only at the early postoperative period (p=0.004).In CTDA group, the range of motion increased at the operated segment (p=0.001) and decreased at the caudal segment (p=0.002). In ACDF group, no motion was observed at the operated segment (p=0.001) and the range of motion increased at adjacent segments (p=0.001). A statistically significant difference between ACDF and CTDA was obtained only at the operated (p=0.001) and caudal segments (p≤0.002).Correlation analysis showed no dependence between range of motion influence and regional/global balance values (p>0.5).The intergroup comparison of cervical lordosis (CL) values revealed a statistically significant difference after 6 (p=0.001) and 12 (p=0.001) months. The best results were obtained at ACDF group towards lordosis increase (p=0.001). The relationship between cervical lordosis and arthroplasty of segments C5–C6, C6–C7 (p=0.003; ρ=0.41) was determined using correlation analysis. The correlation between CL and ACDF (p=0.001; ρ=0.72) was also established.cSVA comparison between groups showed no difference at preoperative period (p=0.215), 6 (p=0.20) and 12 (p=0.425) months after surgery. cSVAs at both groups were equally close to normal values.T1 slope changes before and 12 months after surgery were statistically significant at ACDF (p=0.008) and CTDA (p=0.001) groups. T1 slope values comparison between ACDF and CTDA shows statistically significant difference after 12 months (p=0.003). T1 slopes were equally close to normal values 1 year after surgical treatment.ConclusionOver a 12-month observation period, the segmental range of motion was found to have no effect on changes of regional and global balance of the cervical spine. No influence was confirmed of range of motion on adjacent level syndrome development — the syndrome was diagnosed in none of the cases.This study demonstrated the effectiveness of arthroplasty using an Endocarbon endoprosthesis in improving cSVA and T1 slope values, but no significant improvement of CL values after treatment compared to ACDF group.