Can SI joint surgery or repair alter force transfer and contribute to walking pain?

Sacroiliac (SI) fusion or fixation is designed to stabilize a load-bearing interface between the spine and lower limbs. The evidence supports meaningful mechanical change after surgery; whether that change itself causes walking pain is less directly established.

Biomechanical and mechanistic evidence

• Cadaveric studies show SI fusion/fixation significantly reduces SI motion in flexion–extension, lateral bending, axial rotation, and compression. Normal motion is small (approximately 0.16° axial rotation and 0.32 mm translation under body-weight loading), so these changes represent substantial stabilization.
• Finite-element modeling estimates postoperative SI range-of-motion reductions of 27.8%–59.5% across loading planes. Bilateral fusion increased hip reaction force by 6.7% and hip contact stress by 3.25%, consistent with redistribution of load across the pelvis, hip, and lower lumbar region.
• During walking, particularly single-leg stance, SI-region ligaments, joint geometry, and coordinated muscles provide “force closure” against shear and asymmetric pelvic loading. Altered rigidity or motion can therefore plausibly change pelvic displacement and stress patterns.

Clinical implications

• Fusion generally improves rather than worsens SI-related symptoms: a prospective multicenter cohort found a mean 49-point SI-pain reduction at 6 months, and 90% of 94 previously ambulatory patients regained full ambulation by 6 months.
• Nonetheless, altered mechanics may contribute to walking-provoked pain in some individuals. Small prospective data show improved loading symmetry and pelvic motion after unilateral fusion but persistent pelvic obliquity/rotation versus controls; long-term cohorts report residual slower gait and shorter steps despite low pain.
• Persistent postoperative walking pain should not automatically be attributed to force-transfer changes. Nonunion, implant-related problems, and hip or lumbar pain generators can also be relevant.

Bottom line

• SI surgery reliably alters regional force transfer by reducing SI motion and redistributing load. This provides a credible mechanism for walking pain in some patients, but direct evidence that measured postoperative force-transfer changes specifically cause walking pain remains moderate rather than definitive.