A Preliminary Standardization Study of Cervical Spine Angles in Korean Normal Adult Men and Women According To Pillow Height in The Supine Position

Abstract

Purpose: The purpose of this study was to measure the cervical angle in healthy adults in the supine position and to establish a standardized reference value for cervical alignment.

Methods: Fifty-four healthy adults who voluntarily agreed to participate in the study were recruited. Participants maintained a static supine position on a pillow for 1 min. A three-dimensional motion analysis system was used to measure changes in the Z-coordinate positions of markers placed at C1, C4, and C7. A towel was placed on a firm floor, and the pillow was positioned parallel to the X-axis of the motion analysis system, with one corner aligned with the coordinate origin. The participant's head was positioned at the center of the pillow, and movement and conversation were restricted during the measurement period. Cervical angles were calculated based on temporal changes in marker positions and analyzed as an indicator of cervical alignment.

Results: After 1 min, the mean cervical angle was 175.54 ± 2.16° in men, 175.79 ± 2.34° in women, and 175.66 ± 2.22° in the total sample. No significant differences in cervical angle or changes in the Z-coordinate positions of C1, C4, and C7 were observed between or within sex groups (p > 0.05). However, height-based analysis revealed significant differences in C1_Z between the 160-cm and >180-cm groups and in C7_Z in the 170-cm group (p < 0.05). Weight-based analysis showed significant differences in C1_Z in the 50–59 kg group and in C4_Z in the 60–69 kg group (p < 0.05), whereas no significant differences were observed among the other height or weight groups (p > 0.05). Post hoc analysis according to cervical alignment type revealed that the straight-neck group showed significant differences in C7_Z compared with the mild straight-neck, normal, mild kyphotic-neck, and kyphotic-neck groups (p < 0.05). These findings suggest that specific anthropometric factors may be partially associated with variations in cervical alignment.

Conclusions: The cervical angle of 175.66° measured in the supine position in this study may serve as a clinical reference value for cervical alignment during a sleep-related posture. This standardized value may provide a useful basis for evaluating sleeping posture and informing the ergonomic design and optimization of pillows.