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

Spinal fusion surgery is often performed with pelvic fixation to prevent distal junctional kyphosis. The inclusion of spinopelvic fixation has been reported to induce progression of hip joint arthropathy in a radiographic follow-up study. However, its biomechanical mechanism has not yet been elucidated. This study aimed to compare the changes in hip joint moment before and after spinal fusion surgery.This study was an observational study and included nine patients (eight women and one man) who were scheduled to undergo spinopelvic fusion surgery. We calculated the three-dimensional external joint moments of the hip during gait, standing, and climbing stairs before and 1 year after surgery.During gait, the maximum extension moment was 0.51 ± 0.29 and 0.63 ± 0.40 before and after spinopelvic fusion surgery (p = 0.011), and maximum abduction moment was 0.60 ± 0.33 and 0.83 ± 0.34 before and after surgery (p = 0.004), respectively. During standing, maximum extension moment was 0.76 ± 0.32 and 1.04 ± 0.21 before and after spinopelvic fusion surgery (p = 0.0026), and maximum abduction moment was 0.12 ± 0.20 and 0.36 ± 0.22 before and after surgery (p = 0.0005), respectively. During climbing stairs, maximum extension moment was - 0.31 ± 0.30 and - 0.48 ± 0.15 before and after spinopelvic fusion surgery (p = 0.040), and maximum abduction moment was 0.023 ± 0.18 and - 0.02 ± 0.13 before and after surgery (p = 0.038), respectively.This study revealed that hip joint flexion-extension and abduction-adduction moments increased after spinopelvic fixation surgery in the postures of standing, walking, and climbing stairs. The mechanism was considered to be adjacent joint disease after spinopelvic fusion surgery including sacroiliac joint fixation.