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Minimum 2-Year Analysis of Sacropelvic Fixation and L5–S1 Fusion Using S1 and Iliac Screws

Study Design. An analysis of lumbosacral fusions for high-grade spondylolisthesis fusions with reduction and long fusions to the sacrum in ambulatory adults. Objective. To assess the clinical and radiographic results of lumbosacral fusions using bilateral S1 and iliac screws. Summary of Background Data. S1 screws often fail with lumbosacral fusions, whereas L5–S1 pseudarthrosis is common in patients with deformity. Materials and Methods. A total of 81 patients (38 revision, 43 primary) with minimum 2-year follow-up (average, 4.2 years; range, 2.0–7.1 years) underwent L5–S1 fusion using S1 and iliac screws (158 screws). Forty-nine of 81 constructs (61%) included an anterior load-sharing/fixation device. Group 1 included isthmic spondylolisthesis (n = 42), whereas Group 2 included long fusions (≥3 levels) to the sacrum (n = 39). In Group 2, 15 patients (Group 2A) were fused from L1, L2, or L3 to the sacrum (3–5 levels, average 3.3 levels) and 24 patients (Group 2B) were fused from the thoracic spine to the sacrum (6–17 levels, average 11.5 levels). Twelve patients had pseudarthrosis at L5–S1. A patient questionnaire was completed. Results. A total of 36 of the 38 revision patients had previous iliac crest harvesting, yet iliac screws were placed in 34 of 36 patients. Overall, 78 of 80 patients had iliac crest harvesting (one not attempted). None had loss of screw fixation or iliac crest fracture after harvesting. Four of the 81 patients (4.9%) had pseudarthrosis at L5–S1 after reconstruction. This included solid fusion in 10 of 12 patients presenting with L5–S1 pseudarthrosis. Fourteen percent of patients experienced some discomfort over the iliac screws; however, only one patient required screw removal. Conclusions. Bilateral iliac screws coupled with bilateral S1 screws provide excellent distal fixation for lumbosacral fusions with a high fusion rate (95.1%) in high-grade spondylolisthesis and long fusions to the sacrum. Previous iliac crest harvesting does not prevent ipsilateral screw placement (34 of 36 patients) or additional iliac harvesting (78 of 80 patients).