Our results provide a quantitative and objective evaluation of the effect of pillow height on the biomechanics of the head-neck complex, and have application in pillow design and selection. The cranio-cervical pressures and cervical spine alignment were height-specific, and they were believed to reflect quality of sleep. Pillow height elevation significantly increased the average and peak pressures of the cranial and cervical regions, and increased the extension and lordosis of the cervical spine. With respect to cervical spine alignment, raising pillow height from H0 to H3 caused an increase of 66.4% and 25.1% in cervical angle and lordosis distance, respectively, and a reduction of 43.4% in kyphosis distance. The peak cervical pressures at pillow heights H2 and H3 were significantly different from that at H0 ( p < 0.05). The average cervical pressure at pillow height H0 was 65% lower than that at H3, and significantly different from those at H1 and H2 ( p < 0.05). The average cranial pressure at pillow height H3 was approximately 30% higher than that at H0, and significantly different from those at H1 and H2 ( p < 0.05). Three spine alignment parameters (cervical angle, lordosis distance and kyphosis distance) were identified.

The coordinate of the center of each cervical vertebra were predicted for each pillow height. Cervical spine alignment was studied using a finite element model constructed based on data from the Visible Human Project. The cranio-cervical pressure distribution over the pillow was recorded the peak and average pressures for each pillow height were compared by one-way ANOVA with repeated measures. The subjects lay on pillows of four different heights (H0, 110 mm H1, 130 mm H2, 150 mm and H3, 170 mm). The average height, weight, and neck length were 167 ± 9.3 cm, 59.6 ± 11.9 kg, and 12.9 ± 1.2 cm respectively. Ten healthy subjects (five males) aged 26 ± 3.6 years were recruited. We aimed to evaluate the effect of pillow height on cranio-cervical pressure and cervical spine alignment. While appropriate pillow height is crucial to maintaining the quality of sleep and overall health, there are no universal, evidence-based guidelines for pillow design or selection.

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