In vivo spinal posture during upright and reclined sitting in an office chair

Roland Zemp, William R Taylor, Silvio Lorenzetti, Roland Zemp, William R Taylor, Silvio Lorenzetti

Abstract

Increasing numbers of people spend the majority of their working lives seated in an office chair. Musculoskeletal disorders, in particular low back pain, resulting from prolonged static sitting are ubiquitous, but regularly changing sitting position throughout the day is thought to reduce back problems. Nearly all currently available office chairs offer the possibility to alter the backrest reclination angles, but the influence of changing seating positions on the spinal column remains unknown. In an attempt to better understand the potential to adjust or correct spine posture using adjustable seating, five healthy subjects were analysed in an upright and reclined sitting position conducted in an open, upright MRI scanner. The shape of the spine, as described using the vertebral bodies' coordinates, wedge angles, and curvature angles, showed high inter-subject variability between the two seating positions. The mean lumbar, thoracic, and cervical curvature angles were 29 ± 15°, -29 ± 4°, and 13 ± 8° for the upright and 33 ± 12°, -31 ± 7°, and 7 ± 7° for the reclined sitting positions. Thus, a wide range of seating adaptation is possible through modification of chair posture, and dynamic seating options may therefore provide a key feature in reducing or even preventing back pain caused by prolonged static sitting.

Figures

Figure 1
Figure 1
Wooden MRI-compatible prototype office chair in the upright (a) and the reclined positions (b), together with the corresponding MR images of subject 2, the only subject exhibiting vertebral degenerative changes (at the level L5-S1) (bottom), including the calculated parameters (c). Coordinate system (red arrows), lumbar (α1), thoracic (α2), and cervical (α3) curvature angles (green), exemplary wedge angle of TH9/TH10 (αw), and quadrangle constructed using the two endplates and the ventral and dorsal margins of the vertebral body to calculate the midpoint of each vertebra (blue quadrangle).
Figure 2
Figure 2
Coordinates of the midpoints of the vertebrae (L1-C2) of the upright (blue), reclined (red), together with the coordinates corrected for the 25° reclined seating positions (brown). All curves were related to the same origin, represented by the midpoint of L5.
Figure 3
Figure 3
Wedge angles of the intervertebral discs shown for each subject relative to the spine locations (image adapted from [14]) for both upright (blue) and reclined (red) seating positions. Peak changes in wedge angles of up to ~12° were observed, but the locations were inconsistent across subjects.
Figure 4
Figure 4
Lumbar (α1), thoracic (α2), and cervical (α3) curvature angles in the upright and reclined sitting positions for the five subjects. Note that these section curvature angles include not only the vertebral disk wedge angles, but also the geometrical curvature of the individual vertebral bodies.

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