Mechanical complications and radiographic outcomes following sacral-only versus spinopelvic fixation in long-segment fusion terminating at the sacrum: a retrospective cohort study

PURPOSE: Long-segment fusion terminating at the sacrum is associated with a substantial risk of distal mechanical complications, including screw loosening and pseudarthrosis. Whether spinopelvic fixation is associated with improved construct durability and maintenance of sagittal alignment compared with sacral-only fixation remains clinically relevant. METHODS: This retrospective single-center cohort study included 100 adult patients undergoing posterior long-segment fusion involving four or more motion segments terminating at the sacrum between 2000 and 2024. Patients were stratified into sacral-only fixation and spinopelvic fixation groups. Radiographic outcomes included screw loosening, pseudarthrosis, sagittal vertical axis (SVA), and pelvic incidence-lumbar lordosis (PI-LL) mismatch. Clinical outcomes were assessed using the Oswestry Disability Index (ODI) over a standardized two-year follow-up. RESULTS: Baseline characteristics were comparable between groups, although anterior lumbar interbody fusion (ALIF) at L5-S1 was performed more frequently in the spinopelvic fixation group (46% vs. 14%, p < 0.001). Sacral-only fixation was associated with higher rates of pseudarthrosis (48% vs. 12%, p < 0.001) and clinically relevant screw loosening (34% vs. 6%, p = 0.004). Spinopelvic fixation was associated with better maintenance of PI-LL mismatch during follow-up, whereas final SVA values were comparable between groups. Both groups demonstrated clinically meaningful functional improvement, although recovery occurred earlier in the spinopelvic fixation cohort. CONCLUSION: Spinopelvic fixation was associated with lower rates of distal mechanical complications and improved maintenance of postoperative spinopelvic alignment following long-segment fusion terminating at the sacrum. Given the retrospective study design and the unequal distribution of ALIF, these findings should be interpreted as hypothesis-generating rather than causal but may support consideration of spinopelvic fixation in patients at increased risk of distal construct failure.