Thoracic Inlet Angle Is Associated With Cervical Sagittal Alignment and Recovery After Multilevel Posterior Cervical Fusion

STUDY DESIGN: Retrospective study. OBJECTIVE: This study explores the associations between thoracic inlet angle (TIA) and key cervical alignment measures, including T1 slope (T1S), cervical lordosis (CL), and cervical sagittal vertical alignment (cSVA), to provide insight into alignment relationships and postoperative recovery following multilevel posterior cervical fusion. Patients were stratified using an exploratory preoperative TIA-CL difference (PreopΔ) to examine descriptive recovery patterns in the context of demographic factors such as body mass index (BMI), age, and smoking status. SUMMARY OF BACKGROUND DATA: TIA is a morphologic, anatomically fixed parameter that has been shown to correlate with cervical sagittal alignment. However, its association with postoperative recovery patterns remains incompletely defined, and its role is distinct from validated mismatch parameters such as T1S-CL. METHODS: A total of 157 patients undergoing multilevel posterior cervical fusion were analyzed for associations between TIA and T1S, CL, and cSVA at preoperative, 1-month, 1-year, and 2-year time points. Patients were stratified into 3 exploratory subgroups based on PreopΔ (TIA-CL) values. RESULTS: Significant associations were observed between TIA and T1S ( r =0.76, P <0.001) and between TIA and CL ( r =0.63, P <0.001). Subgroup analyses demonstrated descriptive differences in radiographic and functional outcomes; however, demographic factors such as BMI, age, and smoking status differed between groups and were strongly associated with outcome variability. Among patients in the lowest PreopΔ subgroup, smokers demonstrated higher 2-year ODI scores ( P <0.001). CONCLUSIONS: TIA is anatomically associated with cervical sagittal alignment and provides a morphologic reference for understanding postoperative alignment patterns. Observed subgroup differences represent descriptive, hypothesis-generating associations rather than predictive or causal relationships.