Spine deformity · 2026
Biomechanical analysis in hip joints according to sagittal pelvic tilt in non-ambulatory flaccid neuromuscular scoliosis: a finite element study.
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Shin Jae Won, Kim Dong Ki, Kim Sang Ho, Suk Kyung Soo, Moon Seong Hwan, Park Si Young, Lee Byung Ho, Kwon Ji Won, Lee Sung Jae, Kim Hak Sun
Аннотация
PURPOSE: To quantify the biomechanical effect of postoperative sagittal pelvic tilt (SA-PT) on hip joint stress and to relate the simulation findings to clinically observed hip migration and pain in non-ambulatory patients with flaccid neuromuscular (NM) scoliosis.
METHODS: Three representative postoperative CT scans (SA-PT + 30°, 0°, -15°) were segmented and mirrored to create symmetric pelvis-femur models. Cartilage was modeled as a 1.0 mm isotropic elastic layer. Five SA-PT angles (-30° to + 30°) were simulated by rotating the pelvis around the bicoxofemoral axis. A 400 N compressive load was applied vertically to S1; the distal posterior femur was fixed to simulate seating. Frictionless cartilage-cartilage contact was used. Mesh convergence was confirmed (< 5% PVMS change), and peak von Mises stress (PVMS) and contact force vectors were extracted. Correlations between ΔPVMS and clinical changes in Reimers migration percentage (RMP) and pain VAS were analyzed using Spearman tests; multivariable regression assessed predictors of PVMS.
RESULTS: Mean right hip PVMS decreased with increasing SA PT: -30° 22.4 MPa, -15° 21.6 MPa, 0° 18.1 MPa, + 15° 16.8 MPa, + 30° 9.4 MPa. PVMS at -15° was 38% higher than at + 15°. Stress shifted from central (SA-PT + 30°) to superomedial (-30°). ΔPVMS correlated with ΔRMP (ρ = 0.46, p < 0.001) and ΔVAS (ρ = 0.41, p = 0.002). SA-PT was an independent PVMS predictor (β = -0.37 MPa/5°, p < 0.001).
CONCLUSIONS: Postoperative reduction in SA-PT increases acetabular cartilage stress and produces an unfavorable superomedial load shift that mirrors the clinically observed rise in hip migration and pain.
METHODS: Three representative postoperative CT scans (SA-PT + 30°, 0°, -15°) were segmented and mirrored to create symmetric pelvis-femur models. Cartilage was modeled as a 1.0 mm isotropic elastic layer. Five SA-PT angles (-30° to + 30°) were simulated by rotating the pelvis around the bicoxofemoral axis. A 400 N compressive load was applied vertically to S1; the distal posterior femur was fixed to simulate seating. Frictionless cartilage-cartilage contact was used. Mesh convergence was confirmed (< 5% PVMS change), and peak von Mises stress (PVMS) and contact force vectors were extracted. Correlations between ΔPVMS and clinical changes in Reimers migration percentage (RMP) and pain VAS were analyzed using Spearman tests; multivariable regression assessed predictors of PVMS.
RESULTS: Mean right hip PVMS decreased with increasing SA PT: -30° 22.4 MPa, -15° 21.6 MPa, 0° 18.1 MPa, + 15° 16.8 MPa, + 30° 9.4 MPa. PVMS at -15° was 38% higher than at + 15°. Stress shifted from central (SA-PT + 30°) to superomedial (-30°). ΔPVMS correlated with ΔRMP (ρ = 0.46, p < 0.001) and ΔVAS (ρ = 0.41, p = 0.002). SA-PT was an independent PVMS predictor (β = -0.37 MPa/5°, p < 0.001).
CONCLUSIONS: Postoperative reduction in SA-PT increases acetabular cartilage stress and produces an unfavorable superomedial load shift that mirrors the clinically observed rise in hip migration and pain.