Effect of reclining angle on lumbar lordosis at driving posture: A radiological evaluation

Abstract

BACKGROUND:

Optimal seatback angles for automobile drivers’ seats have been investigated based on comfort and back muscle activities; however, radiology supported evidences are scarce.

OBJECTIVE:

The aim of this study was to evaluate optimal range of the seatback reclining regarding torso angles for an automobile driver’s seat to preserve lumbar lordosis.

METHODS:

Thirty-one healthy volunteers were recruited among five body type categories. Lateral lumbar spine X-rays were obtained for the neutral sitting posture without seatback (reference), and with reclining angles of 23 ${}^{\circ }$ to 33 ${}^{\circ }$ by 2 ${}^{\circ }$ intervals. The Cobb angles for the L1-L4, L4-S1, and L1-S1 segments were measured.

RESULTS:

The Cobb angle for L4-S1 was nearest to the reference (18.74 $\pm$ 1.57 ${}^{\circ }$ , mean $\pm$ standard error mean) at reclining angles of 29 ${}^{\circ }$ and 31 ${}^{\circ }$ (14.51 $\pm$ 1.41 ${}^{\circ }$ and 14.47 $\pm$ 1.43 ${}^{\circ }$ , respectively). The Cobb angle at L4-S1 between reclining angles of 27 ${}^{\circ }$ (12.02 $\pm$ 1.31 ${}^{\circ }$ ) and 29 ${}^{\circ }$ (14.51 $\pm$ 1.41 ${}^{\circ }$ ) were significantly different ( $p<$ 0.001). Tall men showed relatively preserved lordosis angles at all reclining angles. Fat men and short women demonstrated prominent loss of lordosis with excessively kyphotic L1-L4 segment.

CONCLUSIONS:

Reclining angles of 29 ${}^{\circ }$ to 31 ${}^{\circ }$ revealed to be optimal for preserving lordosis at the L4-S1 segment. Individualized healthcare-related guideline for driver’s seat adjustment setting is necessary.