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.