Comparison of sacroiliac joint stress distribution between femoroacetabular impingement and developmental dysplasia of the hip: A finite element analysis study.

Abstract

Femoroacetabular impingement (FAI) and developmental dysplasia of the hip (DDH) are hip disorders that may be accompanied by sacroiliac joint (SIJ) pain. Although both conditions are considered to alter load transmission across the pelvic ring, differences in SIJ stress patterns between FAI and DDH remain unclear. The purpose of this study was to compare SIJ stress distribution and stress characteristics between FAI and DDH using finite element analysis (FEA). This retrospective image-based FEA study included preoperative computed tomography data from 30 hips with FAI and 20 hips with DDH. Three-dimensional models of the pelvis, sacrum, and femur, including SIJ cartilage and surrounding ligaments, were reconstructed. A 90° hip flexion model with a 600 N compressive load applied at L5 was analyzed. The SIJ was divided into superior, middle, and inferior regions, and regional tensile, compressive, and shear stresses were quantified. The direction of stress vectors was assessed qualitatively by visual inspection of vector diagrams to characterize dominant load transmission patterns. In the middle and superior regions of the SIJ, tensile, compressive, and shear stresses were significantly higher in DDH than in FAI (all p < 0.001). In the inferior region, tensile and shear stresses were significantly higher in DDH, whereas compressive stress was significantly higher in FAI (all p < 0.001). Stress vectors were oriented predominantly perpendicular to the SIJ surface in FAI and approximately parallel to the SIJ surface in DDH. Finite element analysis revealed distinct SIJ stress patterns between FAI and DDH. FAI was characterized by increased compressive stress in the inferior region of the SIJ, whereas DDH showed higher tensile and shear stresses across multiple regions. These findings suggest disease-specific load transmission mechanisms across the pelvic ring and may provide biomechanical insights into SIJ loading associated with different hip pathologies.