This cross-sectional study aimed to characterize cervical rotational kinematics under physiological upright, weight-bearing positions using upright multidetector CT (MDCT) and to clarify the associations between rotational range of motion (ROM), age, sex, and cervical sagittal alignment. Forty-nine healthy volunteers—24 younger (21–40 years) and 25 elderly (61–79 years)—underwent upright MDCT in natural standing and maximal right cervical rotation. Rotational angles from the occiput to C7 were measured relative to T1. Key parameters included segmental rotational ROM (rsd: the change in intervertebral rotation from neutral to maximal position), rotated segmental position (rd: the intervertebral rotation between adjacent vertebrae at maximal rotation), and percentage contribution of each segment (%rsd). 

The results revealed that the largest segmental ROM occurred at C1–2 (rsdC1: 34.3°), providing a dominant %rsdC1 of 66.1%, while %rsd for C2–C7 segments remained low, ranging from 2.4% to 8.6%. Compared with younger participants, the elderly group showed significantly reduced total rotation and lower rsdC1 (30.3° vs. 37.0°, p=0.008). Correlation analysis showed that rsdC1 correlated negatively with age (r = –0.31), whereas rsd at C7–T1 correlated positively (r = 0.29). Multivariable regression for rsdC1 identified elderly age as the only significant negative predictor (β = -5.99, p=0.004), whereas sex, BMI, and sagittal parameters were not significant. In contrast, rdC1 was independently associated with multiple factors: elderly age (β = -6.05, p < 0.001), male sex (β = -5.30, p=0.003), and a smaller C2–7 angle (β= -0.14, p=0.020).

In conclusion, under physiological weight-bearing conditions, cervical rotation is predominantly generated at C1–2. Aging reduces segmental rotational ROM at the upper cervical levels, which may lead to compensatory motion at the cervicothoracic junction. Regression analysis highlights that while rotational ROM is primarily affected by aging, the intervertebral position at maximal rotation is independently influenced by age, sex, and sagittal alignment. These findings provide essential normative data and underscore the importance of evaluating cervical kinematics under physiological upright, load-bearing conditions.