The Effect of Standing and Different Sitting Positions on Lumbar Lordosis: Radiographic Study of 30 Healthy Volunteers

Abstract

Study design: Radiographic review of healthy volunteers.

Purpose: To determine the ideal sitting positions by measuring changes in lumbar lordosis (LL) and pelvic parameters (PPs) in various positions.

Overview of literature: Prolonged sitting is generally accepted as an important risk factor for low back pain (LBP). It is now recognized that spinopelvic alignment is important for maintaining an energy-efficient posture.

Methods: Lateral spine radiographs of thrirty healthy volunteers (male participants) were taken in standing and five sitting positions. Radiographic measurement of LL and PPs was performed in each position. Statistical analysis was performed to identify a correlation between changes in the LL and PPs in each positions.

Results: LL in standing was 48.5°±8.7°. Sitting significantly decreased LL and segmental angle when compared with standing (p<0.05). The lower lumbar segmental angles (L4-5 and L5-S1) significantly decreased in all sitting positions (p<0.05), but the decrease was relatively less on the chair with lumbar support and in the 90°-angled chair. The sacral slope (SS) decreased and the pelvic tilt increased with decreasing LL in the sitting positions.

Conclusions: Sitting causes a reduction in LL and SS when compared with standing. It might cause a spinopelvic imbalance and result in chronic LBP. Our study showed that sitting on a chair with back support induced minimal changes to LL. Consequently, it is proposed that sitting on a chair with back support would be a much more ideal position than sitting on other types of chairs.

Keywords: Chair; Low back pain; Lumbar lordosis; Sitting.

Fig. 1. Standing position, the subject stood in a comfortable position, with the knees fully extended and the hands placed behind the head.

Fig. 2. Five sitting positions with their corresponding radiograph. (A) The subject sat on chair with back support, (B) sitting on 90° angled chair, (C) sitting on chair with anterior support, (D) sitting on stool, (E) sitting cross-legged.

Fig. 3. Representative lumbar lordosis (α) and lumbar segmental lordosis (β) from one subject on standing position; lumbar lordosis (L1-S1) was measured using method proposed by Legaye et al. [17] and lumbar segmental lordosis (L4-5) was measured using Cobb method and measured in similar fashion from L1-2, L2-3, L3-4, and L5-S1.

Fig. 4. Pelvic incidence, sacral slope and pelvic tilt on standing position. Pelvic incidence is the angle between the line perpendicular to the middle of the cranial sacral end plate and the line joining the middle of the cranial sacral end plate with the center of the bicoxofemoral axis (the line between the geometric center of both femoral heads). Sacral slope is the angle between the horizontal line and the cranial sacral end-plate tangent. Pelvic tilt is the angle between the vertical line and the line joining the middle of the sacral plate with the center of the bicoxofemoral axis.

Fig. 5. Lumbar segmental angle on standing and five sitting positions. Positive segmental angles refer to a lordotic posture. Sacral slope (sacral horizontal angle) indicates sacral horizontal angle.

Fig. 6. Data scattergram of correlation (A) between lumbar lordosis and sacral slope, and (B) between lumbar lordosis and pelvic tilt.