How Does Spino-Pelvic Fixation Affect Post-Operative Compensatory Mechanisms in Adult Spinal Deformity?

Area of Science:

• Spine surgery
• Orthopedics
• Biomechanical engineering

Background:

• Adult spine deformity (ASD) often requires complex surgical correction with spino-pelvic fixation.
• Maintaining sagittal balance post-operatively is crucial for functional outcomes.
• Pelvic fixation methods, such as S2-alar-iliac (S2AI) screws and iliac screws (IS), aim to stabilize the spine and pelvis.

Purpose of the Study:

• To compare the post-operative compensatory mechanisms of sagittal balance between S2AI and IS pelvic fixation in patients with ASD.
• To evaluate how different pelvic fixation types influence pelvic tilt, sacral slope, and knee flexion post-surgery.

Main Methods:

• Retrospective cohort study at a single center involving multiple surgeons.
• Included ASD patients with a post-operative PI-LL mismatch >10° after spino-pelvic fixation.
• Analyzed pre-operative and 1-year follow-up EOS imaging data for various spinal and pelvic parameters, comparing changes between S2AI and IS groups.

Main Results:

• Both S2AI (n=53) and IS (n=26) groups were comparable at baseline.
• S2AI group showed significantly greater changes in sacral slope (ΔSS: 9.87° vs 13.2°, P=.001) and knee flexion angle (ΔKFA: 6.01° vs 3.06°, P=.02) compared to the IS group.
• Changes in pelvic tilt (ΔPT) were similar between groups (P=.42).

Conclusions:

• Pelvic fixation type significantly affects post-operative sagittal balance compensation in ASD patients.
• S2AI screws promote greater compensatory knee flexion and less pelvic compensation compared to IS.
• This difference may be attributed to increased SI joint laxity and mechanical stress on iliac connectors with IS fixation.