P24. Acute failure of S2-alar-iliac pelvic fixation following adult deformity correction

Abstract

BACKGROUND CONTEXT Pelvic fixation with S2-alar-iliac (S2AI) screws is a widely accepted technique in adult deformity surgery, with few descriptions of complications. PURPOSE To report novel acute failure mechanisms in S2AI instrumentation. STUDY DESIGN/SETTING Retrospective chart review. PATIENT SAMPLE N/A OUTCOME MEASURES N/A METHODS We performed a retrospective review of all fusion surgeries extending from L2 or higher with instrumentation to the pelvis in which S2AI screws were placed with at least 6 months follow-up between 3/2017 and 6/2019. We excluded patients under 18 years of age and non-ambulatory patients. Acute instrumentation failure was defined as any case requiring revision of the pelvic fixation within 6 months from the index surgery. We reviewed the demographic and surgical characteristics of each patient, and reviewed preoperative and 6-week postoperative radiographs to document the change in their deformity parameters as well as for the presence of a transitional lumbo-sacral segment. RESULTS A total of 134 cases were identified, of which seven had acute S2AI instrumentation failure requiring revision (5%). Failure cases averaged age 56.6 years, BMI 32.5, 57% female, 12 levels of fusion, and average deformity correction was LL increase 32°, T1PA decrease 19°, and CSVL decrease 3.5cm. Failure mechanism was either set plug dislodgement from S2AI screw heads, sacral fracture/kyphosis with rod slippage out of S2AI set plugs, or both, and involved two different implant manufacturers. Three of seven (43%) failure patients had a nonmobile transitional segment at the lumbosacral junction and fractured through the transitional segment with kyphotic angulation. Salvage strategy involved removal and revision of the original S2AI screws with placement of additional stacked pelvic fixation and a multi-rod construct. CONCLUSIONS We have identified a novel mechanism of pelvic fixation failure involving set screw dislodgement and rod slippage, which affected 5% of the deformity patients in our series across two implant manufacturers. Patients with large angular deformity correction and/or transitional lumbosacral anatomy may be particularly at risk, and may benefit from supplemental pelvic fixation. FDA DEVICE/DRUG STATUS S2AI Screws (Approved for this indication), thoracolumbosacral pedicle screw system (Approved for this indication).