Determination of the amount of leg length inequality that alters spinal posture in healthy subjects using rasterstereography

Abstract

Purpose: Leg length inequalities (LLIs) can result in an increased energy consumption, abnormal gait or osteoarthritis of the hip. In a previous study we simulated different LLIs of up to 15 mm and evaluated their effects on the pelvic position and spinal posture. We found a correlation between LLIs and resulting changes of the pelvic position. Despite suggestions in the literature we were not able to detect significant changes of the spinal posture. Therefore, the purpose of this study was to determine the amount of LLI that would in fact alter the spinal posture.

Methods: The subjects were placed on a simulation platform, whose height could be precisely controlled by the measuring device, to simulate different LLIs of up to 20 mm. For LLIs >20 mm, additional precision-cut wooden blocks were used under one foot. After an adaptation period the resulting changes of the pelvis and spine were measured with a rasterstereographic device.

Results: We found a significant correlation between platform height changes and changes of the pelvic position. The frontal spinal parameters surface rotation and lateral deviation changed significantly when simulating differences greater than 20 mm. No changes of the sagittal spinal curvature were measured, however, a trend to decreasing kyphotic angles was noted.

Conclusions: Our study has shown for the first time that LLIs >20 mm will lead to significant changes in the spinal posture of healthy test subjects. However, these changes were only found in frontal (surface rotation and lateral flexion) spinal parameters, but not in sagittal parameters. Here for the kyphotic angle only a tendency to decreasing angles was noted. We have also found a significant correlation between different leg lengths and changes of the pelvic position. Further, females and males seem to react in the same way to LLIs.

Figures

Fig. 1

The figure shows a test subject standing on the stand platform, which is raised 20 mm on the right side, during a rasterstereographic measurement. The specific dimensions of the constructed platform are included into the figure. When simulating LLIs greater than 20 mm additional precision-cut wooden blocks were placed under the foot

Fig. 2

Pelvic torsion as shown in a is defined as the torsion of the surface normals on the two lumbar dimples [left lumbar dimple (DL) and right lumbar dimple (DR)]. b Illustrates the pelvic obliquity, which is considered as the different height of the two lumbar dimples to each other in degrees. In c the kyphotic angle is illustrated as the angle between the surface tangents on spinous process of the seventh cervical vertebra (VP) and the calculated spinous process of the 12th thoracic vertebrae (T12). The lordotic angle was measured as the angle between the surface tangents on points T12 and the midpoint between the two lumbar dimples (DM)

Fig. 3

a, b Illustrate the surface rotation as the value of the horizontal components of the surface normals on the line of symmetry measured in degrees. The lateral deviation is defined as the deviation of the spinal midline from the line between the VP to DM (midpoint between DL and DR) as shown in c and d

Fig. 4

a Shows the mean pelvic obliquity in millimetres (with the 95 % confidence level) for the simulated different platform heights (0–60 mm) for the right side (positive values) and left side (negative values). An increase in platform height leads to an increase in pelvic obliquity on the corresponding side. b Demonstrates the changes of the pelvic torsion in degrees with the simulated platform heights of up to 60 mm. The changes in pelvic torsion are significant between the neutral position (0 mm) and platform heights ≥20 mm on the right side and ≥30 mm on the left side. No significant differences were found between females and males

Fig. 5

The increase in LLI led to an increase in pelvic obliquity. A significant increase was found on both sides with LLIs of 50 mm and above (p < 0.05). We measured a significant difference (p < 0.05) in the neutral standing position and in all simulated leg lengths between women and men

Fig. 6

a Shows the changes of the frontal parameter surface rotation (with the 95 % confidence level) when raising the platform. Changes between the neutral position (0 mm platform height) and ≥20 mm on the left side and ≥30 mm on the right side are significant. b Shows the increase of the lateral deviation of the spine, when increasing the platform height. No differences between females and males were found

Fig. 7

The figure shows a female test subject during measurements standing on the simulation platform, which was elevated on the right leg side. The elevation of the platform led to a pelvic obliquity, with an elevation of the iliac crest on the long leg side. This pelvic obliquity resulted in a lateral deviation and convexity of the spine towards the short leg side