Sacrospinous and sacrotuberous ligaments influence in pelvis kinematics

Abstract

The alteration in mechanical properties of posterior pelvis ligaments may cause a biased pelvis deformation which, in turn, may contribute to hip and spine instability and malfunction. Here, the effect of different mechanical properties of ligaments on lumbopelvic deformation is analyzed via the finite element method. First, the improved finite element model was validated using experimental data from previous studies and then used to calculate the sensitivity of lumbopelvic deformation to changes in ligament mechanical properties, load magnitude, and unilateral ligament resection. The deformation of the lumbopelvic complex relative to a given load was predominant in the medial plane. The effect of unilateral resection on deformation appeared to be counterintuitive, suggesting that ligaments have the ability to redistribute load and that they play an important role in the mechanics of the lumbopelvic complex.

Keywords: elasticity; finite element method; hip-spine syndrome; lumbopelvic transition; pelvic ligaments; sacroiliac joint.

FIGURE 1

The finite element model of a male pelvis with boundary conditions applied and the sacrospinous and sacrotuberous ligaments is shown. (a) Cranial view of the posterior pelvis, showing the L5 endplate and facet joints (red areas) being loaded superior‐inferiorly (red arrows), (b) posterior–lateral view of the right aspect of the pelvis (red ellipses indicate the sacrospinous‐sacrotuberous complex on both sides).

FIGURE 2

Locations of anatomical points, their directions of translations T, and rotations R within the coordinate system from an anterior–posterior (right image) and medial–lateral view (left image); a, anterior; cd, caudal; cr, cranial; l, left; p, posterior; r, right. Sacroiliac joint, movement of the sacrum (S_L) relative to the ilium (I₁); Lumbosacral transition, movement of the fifth lumbar vertebra (L₅) relative to the sacrum (S_M). Innominate bone, movement of the pubis (P_L) relative to the ilium (I₂); Pubic symphysis, movement of the left relative to the right superior pubic ramus (P_R‐P_L), according to Hammer, Scholze, et al. (2019).

FIGURE 3

Comparison of experimental and computational results (“Soft state”) for relative displacements T (micrometers) and rotations R (millidegrees). The blue area represents mean values ± standard deviation. The orange cross represents results at 500‐N load in the stiff FE model (“Stiffer state”).

FIGURE 4

The sensitivity (slope) of absolute and relative displacements and rotations to loading forces computed with finite elements model “Soft state”.

FIGURE 5

Absolute variations of displacements in (mm) and rotations in (°) for monitored locations under three scenarios “Stiffer state”, “Soft state,” and “Transected state”, respectively. Owing to the small extent in T _x in spite of the vast 1393% change in relative movement, T _x is further magnified (insert) to enhance readability.

FIGURE 6

The relative variations of displacement in (mm) and rotation in (°) for pairs of monitored locations under three scenarios “Stiffer state”, “Soft state”, and “Transected state”, respectively.