The Variability of the Cervicothoracic Inflection Point: A Cohort Analysis of the Multi-Ethnic Asymptomatic Normative Study (MEANS).

Study design: Cross-sectional Cohort Study.

Objective: To determine the cervicothoracic inflection point in an asymptomatic, adult population.

Introduction: The cervicothoracic inflection point (CTIP) is an important sagittal marker to understand for patients with cervical deformities. We aimed to identify the CTIP and understand the relationship to other sagittal alignment markers.

Methods: 468 adult asymptomatic volunteers (18-80 years) from 5 countries (United States, France, Japan, Singapore, Tunisia). All volunteers underwent standing full body, low dose stereo radiographs. The CTIP was identified by measuring the cervical sagittal angle (CSA) and thoracic kyphosis maximum angle (TK_Max), using the end vertebra concept. The CTIP was defined as the vertebra or disc between the lower end vertebra of the CSA and upper end vertebra of TK_Max. A correlation matrix was utilized to identify the relationship between the CTIP and spinopelvic sagittal parameters of interest.

Results: The most common CTIP value was the T1 vertebra. CTIPs ranged from C5 to T4, respectively. CTIP showed a weak positive correlation to age (r = 0.10, P = 0.03) and negative correlation to BMI (r = -0.11, P = 0.04). Additionally, CTIP had a minor positive correlation with OC2-CL, C7 slope, T1 slope, T1PA, T1-T12 TK, and T4-T12 TK, all statistically significant. Linear regression demonstrated increased cervical lordosis and increased TK was associated with more caudal CTIP segments.

Conclusion: CTIP segments ranged from C5 to T4, with the most common segment being T1. Understanding the relationship of the CTIP to other sagittal variables is critical to patients with CD.