Evaluation of 3D vertebral and pelvic position by surface topography in asymptomatic females: presentation of normative reference data

Background Deviations from a conventional physiologic posture are often a cause of complaint. According to current literature, the upright physiological spine posture exhibits inclinations in the sagittal plane but not in the coronal and transverse planes, but individual vertebral body positions of asymptomatic adults have rarely been described using surface topography. Therefore, this work aims to form a normative reference dataset for the thoracic and lumbar vertebral bodies and for the pelvis in all three planes in asymptomatic women. Methods In a prospective, cross-sectional, monocentric study, 100 pain-free asymptomatic women, aged 20–64 years were enrolled. Habitual standing positions of the trunk were measured using surface topography. Data were analyzed in all three planes. Age sub-analysis was: 1) ages ≤ 40 years and 2) ages ≥ 41 years. Two-sample t-tests were used for age comparisons of the vertebral bodies, vertebra prominence (VP)–L4, and global parameters. One-sample t-tests were used to test deviations from symmetrical zero positions of VP–L4. Results Coronal plane: on average, the vertebral bodies were tilted to the right between the VP and T4 (maximum: T2 − 1.8° ± 3.2), while between T6 and T11 they were tilted to the left (maximum: T7 1.1° ± 1.9). T5 and L2 were in a neutral position, overall depicting a mean right-sided lateral flexion from T2 to T7 (apex at T5). Sagittal plane: the kyphotic apex resided at T8 with − 0.5° ± 3.6 and the lumbar lordotic apex at L3 with − 2.1° ± 7.4. Transverse plane: participants had a mean vertebral body rotation to the right ranging from T6 to L4 (maximum: T11 − 2.2° ± 3.5). Age-specific differences were seen in the sagittal plane and had little effect on overall posture. Conclusions Asymptomatic female volunteers standing in a habitual posture displayed an average vertebral rotation and lateral flexion to the right in vertebral segments T2–T7. The physiological asymmetrical posture of women could be considered in spinal therapies. With regard to spinal surgery, it should be clarified whether an approximation to an absolutely symmetrical posture is desirable from a biomechanical point of view? This data set can also be used as a reference in clinical practice. Trial registration: This study was registered with WHO (INT: DRKS00010834) and approved by the responsible ethics committee at the Rhineland–Palatinate Medical Association (837.194.16). Supplementary Information The online version contains supplementary material available at 10.1186/s13018-021-02843-2.

vertical plane (sagittal section) (in mm) or rather is defined by the angle between the plumb line dropped from VP and the line between VP and DM (in degrees).
A positive value means VP is more ventral than DM.

Thoracic Kyphosis Angle [°]
The thoracic kyphosis is calculated by the angle formed between the two surface tangent lines of the ICT (inflection point between cervical and thoracic spine) and ITL (inflection point between thoracic and lumbar spine), based on the spinous process line.

Lumbar Lordosis Angle [°]
The lumbar lordosis is calculated by the angle formed between the two surface tangent lines of the ITL A positive value means that the patient is leaning to the right.

Maximum Apical Deviation [mm]
The maximum apical deviation is measured from the apex of the largest curve -either left or right -in the coronal plane to the line drawn between VP and the DM.
A positive value means a deviation to the right. A line between those two points is drawn and compared with the horizontal line representing the horizon (perpendicular to the gravity line). The angle (in degrees) between them is measured.
A positive value means that the right shoulder is elevated.

Pelvic Obliquity [mm], [°]
The pelvic obliquity is the difference (in mm) between two horizontal lines drawn through both dimples (DL and DR).
A line is drawn from DL to DR and is compared to a horizontal line representing the horizon. The angle (in degrees) between them is measured.
A positive value means that the right pelvis is elevated.

Vertebral Lateral Flexion [°]
The parameter describes the lateral inclination of the vertebra in space (relative to a plumb / gravity line) as

Maximum Surface Rotation [°]
The maximum surface rotation in the transversal plane is defined by the rotation in the axial plane of a spinous process when compared to the neutral pelvis (left dimple -right dimple line in parallel to the coronal plane) is recorded in degrees.
A positive value means a maximum rotation to the right.

3D posture of healthy women Pelvic Rotation [°]
The pelvic rotation is the rotation in the transversal plane of the right dimple relative to a reference coronal plane that is defined from the system setup, perpendicular to the camera-projection axis.
A positive value means the pelvis is rotated to the left when seen from behind (the value is corrected * (-1)).
All 3D The vertebral rotation describes the rotation of a vertebra in the transversal plane (relative to the neutral pelvis).
A positive value means a vertebra is rotated to the left (counterclockwise) when seen from behind.
The rotation of vertebral bodies happens in situ, therefore the direction of rotation between surface and vertebral rotation changes. Hence, a surface rotation to the right, mathematically represented with a +, becomes a vertebral body rotation to the left. This is due to the calculation process in which a vector is used that points from Processus spinosus towards the middle of the vertebral body meaning that the surface rotation changes its direction within the vertebral body.
Definitions and images were assigned by DIERS (© Florian Franke / DIERS) and adapted by Claudia Wolf.