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 degrees to 33 degrees by 2 degrees 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 +/- 1.57 degrees, mean +/- standard error mean) at reclining angles of 29 degrees and 31 degrees (14.51 +/- 1.41 degrees and 14.47 +/- 1.43 degrees, respectively). The Cobb angle at L4-S1 between reclining angles of 27 degrees (12.02 +/- 1.31 degrees) and 29 degrees (14.51 +/- 1.41 degrees) 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 degrees to 31 degrees revealed to be optimal for preserving lordosis at the L4-S1 segment. Individualized healthcare-related guideline for driver's seat adjustment setting is necessary.