Age- and sex-related differences in physiological rotation patterns of the cervical spine: A detailed upright multidetector CT analysis.

BACKGROUND: Cervical segmental rotation has rarely been quantified in physiological upright, weight-bearing positions. This study aimed to characterize cervical rotational kinematics using upright multidetector CT (MDCT) and to evaluate the independent associations between rotational parameters, age, sex, and cervical sagittal alignment. METHODS: Forty-nine healthy volunteers-24 younger (21-40 years) and 25 elderly (61-79 years)-underwent upright MDCT in an upright standing position and maximal right cervical rotation. Rotational angles (O-C7) were measured relative to T1. Parameters included segmental rotational range of motion (ROM) (rsd: intervertebral rotation change from neutral to maximal rotation), rotated segmental position (rd: intervertebral rotation at maximal rotation), and percentage segmental contribution (%rsd). RESULTS: The largest segmental ROM occurred at C1-2 (median rsdC1: 34.3°), accounting for 66.1% of total rotation. Compared with younger participants, the elderly group showed significantly reduced total rotation and rsdC1 (30.3° vs. 37.0°, p = 0.008). Correlation analysis showed that age correlated negatively with rsdC1 (r = -0.31) and positively with rsdC7 (r = 0.29). Multivariable regression identified elderly age as a significant negative predictor of rsdC1 (β = -5.59, p = 0.004). In contrast, rdC1 was independently associated with age (β = -6.05, p < 0.001), male sex (β = -5.30, p = 0.003), and smaller C2-7 angle (β = -0.14, p = 0.020). CONCLUSIONS: Under physiological weight-bearing conditions, cervical rotation is predominantly generated at C1-2. Aging reduces upper cervical segmental ROM, potentially leading to compensatory motion at the cervicothoracic junction. While rotational ROM is primarily dictated by age, the intervertebral position at maximal rotation is independently influenced by age, sex, and sagittal alignment. These normative data may serve as a reference for future studies examining cervical disorders and postoperative rotational function.