Effects of sacral slope changes on the intervertebral disc and hip joint: A finite element analysis.

OBJECTIVE: Spinopelvic parameters are vital components that must be considered when treating patients with spinal pathologies. Several finite element studies have explored spinopelvic parameters such as sacral slope (SS) and the impact on the lumbar spine, though no study has examined the effect on the hip and sacroiliac joint (SIJ) on varying SS angles. Therefore, it is necessary to have a biomechanical understanding of the impact on the spinopelvic complex.

METHODS: A finite element (FE) lumbar, pelvis, and femoral model was created from CT scans of a 55-year-old female patient with no abnormalities. Three models were created: a normal model (SS=26°), a model with increased SS (SS=30°), and a model with decreased SS (SS=20°). These models underwent loading for flexion, extension, lateral bending, and axial rotation. Range of motion (ROM), intradiscal pressures, hip joint, and SIJ stresses were analyzed.

RESULTS: The largest SS model (SS=30°) indicated the highest ROM in the L5-S1 (slip angle) level and the highest intradiscal pressures (IDPs). The highest maximum hip and SIJ stresses were present in this model, though the decreased SS model (SS=20°) in extension had the largest stresses for the hip and SIJ.

CONCLUSIONS: The results provide evidence that patients with higher SS may be more prone to increased ROM at the slip angle (L5-S1). Additionally, patients with higher SS showed to have higher stresses on the hip joint and sacroiliac joint, potentially leading to SIJ dysfunction. Clinically, correcting lumbar lordosis (LL) including SS is important, however increasing SS may have a negative impact on the intervertebral disc (IVD), SIJ, and hip joint.