Background: Sacropelvic fixation (SPF) is an integral part of ASD surgery. Literature suggests that combination of S1 and iliac screws may be associated with lowest rate of complications.
Aim: To analyze the rate and potential factors of mechanical failure associated with SPF in adult spinal deformity surgery.
Materials and methods: Of 504 patients enrolled in a prospective multicentric database, 239 were treated conservatively and 265 were treated surgically. Forty-five of those who had sacroiliac fixations and with >6 months (or to failure) f/up constitute the population. Type of iliac fixation was S2 alar/iliac (S2AI) screws in 20 (44.4%) and iliac screws with lateral connectors (IwL) in 25 (55.6%). Diagnoses were degenerative in 20, failed back in 11 and other in 14. Average instrumentation length was 11.6 ± 4.0 levels. Cases with failure were compared to those without using Fisher's Exact and Mann-Whitney U tests.
Results: A total of 16 implant related complications were identified (35.6%). Failures were identified on an average of 224.1 days (8-709) following index surgery. Failure rate of S2AI screws was 35 vs. 12% for IwL screws (p > 0.05). All broken screws were associated with S2AI technique with polyaxial screws. Comparison of failed cases to others revealed that failed cases had inadequate restoration of Lumbar Lordosis but this was not statistically insignificant. Only age was a significantly different, patient with failure being older.
Discussion: Pelvic fixation is still associated with a very high rate of mechanical failure. Major risk factors appear to be age and type of fixation. Although could not be shown to be statistically significant, failure to restore the optimal sagittal balance may be a contributing factor as well. So in conclusion, in cases with suboptimal sagittal plane correction, S2AI with polyaxial screws seem to have higher risk of short-term acute failure compared to IwL.