X-ray characterization of lumbar spine, pelvic, and femur posture in professional motorsports drivers seated in customized seat inserts

Objective Mitigating thoracolumbar spine injury in motorsports drivers remains a challenge. The use of human body models (HBMs) presents an avenue for novel countermeasure development, but the precise posture of the lumbar spine in motorsports seats has not been characterized. The objective of this study was to quantify lumbar spine, pelvis, and femur posture of professional motorsports drivers.Methods Twelve professional motorsport drivers were recruited (WFU School of Medicine IRB: IRB00122615). For each participant, two lateral X-rays were acquired using a reduced-exposure protocol. The imaging captured the inferior thoracic spine, lumbar spine, pelvis, and proximal femurs of drivers seated in custom-molded seat inserts within a portable buck. The buck was equipped with an adjustable steering wheel and footrest to match race-day posture. Fiducial markers 25.4 mm apart enabled image merging, scaling, and alignment. A narrow gage wire in the seat’s midline was used to identify the seat surface at the midplane. Images were merged using custom scripts and annotated. Vertebral body outlines, sacrum, ASIS–PSIS line, femur line, and mid-vertebrae splines were digitized and exported as .igs files. Intervertebral distances, pelvic tilt, femur angles, lumbar lordosis (L5–L1 and L1–sacrum), and orthogonal distances from vertebral midpoints to the seatback were computed for each subject. Surface scans of each unoccupied seat insert and each driver while seated in the seat were collected and aligned with the X-ray data. Statistical analyses include descriptive metrics, boxplots, linear regressions and Spearman’s rank correlations between posture measures and anthropometry.Results Participant age and mass were 28.2 ± 4.9 years and 80.0 ± 10.5 kg. Lumbar curvature was mildly lordotic, with L5–L1 lordosis measuring 2.75 ± 9.3°. Substantial inter-individual variability was observed, with some subjects exhibiting kyphotic or near-neutral curvature despite similar seatback angles (60.2 ± 4.5°). Intervertebral distances followed expected anatomical patterns, peaking at L3–L4 or L4–L5. Femur angles averaged 35.3 ± 5.4° relative to horizontal, and pelvic tilt (ASIS-PSIS w.r.t. horizontal) averaged 30.3 ± 8.4°. Body weight was predictive of posture demonstrating a correlation with L5–L1 lumbar angle approaching significance (p = 0.056). Distances from vertebral midpoints to the seatback increased caudally, peaking at L4 (mean 84.8 ± 8.1 mm). Digitized mid vertebral splines yielded corridors and a characteristic average shape for use in HBM positioning.Conclusions This study provides the first X-ray–based quantification of lumbar spine, pelvic, and femur posture in professional motorsports drivers seated in real-world race environments. The data establishes representative spinal curvature, posture corridors, and geometry critical for accurate HBM posturing. Salient findings include: 1. Driver weight is correlated to lumbar posture and 2. Both kyphotic and lordotic lumbar spine curvature was observed within the sample. These data can be used to support accurate HBM posturing for improved assessment of spinal injury mechanisms and countermeasure development.