Lumbar Fusion including Sacroiliac Joint Fixation Increases the Stress and Angular Motion at the Hip Joint: A Finite Element Study

Abstract

Introduction: Adult spinal fusion surgery improves lumbar alignment and patient satisfaction. Adult spinal deformity surgery improves saggital balance not only lumbar lesion, but also at hip joint coverage. It was expected that hip joint coverage rate was improved and joint stress decreased. However, it was reported that adjacent joint disease at hip joint was induced by adult spinal fusion surgery including sacroiliac joint fixation on an X-ray study. The mechanism is still unclear. We aimed to investigate the association between lumbosacral fusion including sacroiliac joint fixation and contact stress of the hip joint.Methods: A 40-year-old woman with intact lumbar vertebrae underwent computed tomography. A three-dimensional nonlinear finite element model was constructed from the L4 vertebra to the femoral bone with triangular shell elements (thickness, 2 mm; size, 3 mm) for the cortical bone's outer surface and 2-mm (lumbar spine) or 3-mm (femoral bone) tetrahedral solid elements for the remaining bone. We constructed the following four models: a non-fusion model (NF), a L4-5 fusion model (L5F), a L4-S1 fusion model (S1F), and a L4-S2 alar iliac screw fixation model (S2F). A compressive load of 400 N was applied vertically to the L4 vertebra and a 10-Nm bending moment was additionally applied to the L4 vertebra to stimulate flexion, extension, left lateral bending, and axial rotation. Each model's hip joint's von Mises stress and angular motion were analyzed.Results: The hip joint's angular motion in NF, L5F, S1F, and S2F gradually increased; the S2F model presented the greatest angular motion.Conclusions: The average and maximum contact stress of the hip joint was the highest in the S2F model. Thus, lumbosacral fusion surgery with sacroiliac joint fixation placed added stress on the hip joint. We propose that this was a consequence of adjacent joint spinopelvic fixation. Lumbar-to-pelvic fixation increases the angular motion and stress at the hip joint.

Effect of Lumbar Fusion and Pelvic Fixation Rigidity on Hip Joint Stress

“…This study revealed that the DSIF model increased stress and angular motion at the hip joint more than the other models. Previous radiographic 8,10 and biomechanical 9,16 studies have reported that adult spinal deformity surgery influences the hip joint. The results of our study support these previous findings and suggest that more rigid fixation of the pelvis induces additional stress on the hip joint, which may precipitate or accelerate adjacent joint disease.…”

“…To calculate bone density from CT values (in Hounsfield units, HU), the following set of equations was used: ρ (g/cm 3 )=(CT number + 1.4246) × 0.001 / 1.058 (if CT number > −1 HU); ρ (g/cm 3 )=0 (if CT number ≤ −1 HU). The material properties for soft tissues, ligaments, and muscles are listed in Table 1 12–16 . Hip joint cartilage layers were modeled on the acetabular roof and femoral bone, and contact analysis was performed between the cartilage layers of the hip joint.…”

Spinopelvic fusion surgery from lower thoracic spine to pelvis increased hip joint moment–motion analysis

“…The pathology was thoght to be the AJD. A previous finite element study also revealed that the contact pressure of the hip joint was highest in the spinopelvic fixation model, compared with lumbar fusion model without pelvic fixation [ 16 ]. However, there were no reports about the hip-spine relation in three-dimensional motion analysis.…”

Acetabular Rim Fracture after Adult Spinal Deformity Surgery-Induced Secondary Hip Osteoarthritis: Two Case Reports

“…There were no reports on how the stress on the acetabular rim changed after spinal fusion surgery. Hence, we performed finite element analysis to investigate the relationship between spinal fusion and acetabular rim stress using a healthy model from L4 to the femoral model, which was validated by a previous study 4 . In this study, we could not use these cases as patient models because of the influence of implants on computed tomography.…”

“…There are several reports on sacral 5 , iliac crest and rami [6][7][8] , and hip 6,9 fractures. Past studies reported that theymight be due to the stress translation and hypermobility from the fused spine to the next mobile segments 4,10 . We thought that these mechanism was based on adjacent segment disease: the stress shielding within the long spinal fusion construct and induced stress concentration at the distal aspect of the fusion mass.…”