How common is acute pelvic fixation failure after adult spine surgery? A single-center study of 358 patients.

OBJECTIVE: There is a paucity of literature on pelvic fixation failure after adult spine surgery in the early postoperative period. The purpose of this study was to determine the incidence of acute pelvic fixation failure in a large single-center study and to describe the lessons learned. METHODS: The authors performed a retrospective review of adult (≥ 18 years old) patients who underwent spinal fusion with pelvic fixation (iliac, S2-alar-iliac [S2AI] screws) at a single academic medical center between 2015 and 2020. All patients had a minimum of 3 instrumented levels. The minimum follow-up was 6 months after the index spine surgery. Patients with prior pelvic fixation were excluded. Acute pelvic fixation failure was defined as revision of the pelvic screws within 6 months of the primary surgery. Patient demographics and operative, radiographic, and rod/screw parameters were collected. All rods were cobalt-chrome. All iliac and S2AI screws were closed-headed screws. RESULTS: In 358 patients, the mean age was 59.5 ± 13.6 years, and 64.0% (n = 229) were female. The mean number of instrumented levels was 11.5 ± 5.5, and 79.1% (n = 283) had ≥ 6 levels fused. Three-column osteotomies were performed in 14.2% (n = 51) of patients, and 74.6% (n = 267) had an L5-S1 interbody fusion. The mean diameter/length of pelvic screws was 8.5/86.6 mm. The mean number of pelvic screws was 2.2 ± 0.5, the mean rod diameter was 6.0 ± 0 mm, and 78.5% (n = 281) had > 2 rods crossing the lumbopelvic junction. Accessory rods extended to S1 (32.7%, n = 117) or S2/ilium (45.8%, n = 164). Acute pelvic fixation failure occurred in 1 patient (0.3%); this individual had a broken S2AI screw near the head-neck junction. This 76-year-old woman with degenerative lumbar scoliosis and chronic lumbosacral zone 1 fracture nonunion had undergone posterior instrumented fusion from T10 to pelvis with bilateral S2AI screws (8.5 × 90 mm); i.e., transforaminal lumbar interbody fusion L4-S1. The patient had persistent left buttock pain postoperatively, with radiographically confirmed breakage of the left S2AI screw 68 days after surgery. Revision included instrumentation removal at L2-pelvis and a total of 4 pelvic screws. CONCLUSIONS: The acute pelvic fixation failure rate was exceedingly low in adult spine surgery. This rate may be the result of multiple factors including the preference for multirod (> 2), closed-headed pelvic screw constructs in which large-diameter long screws are used. Increasing the number of rods and screws at the lumbopelvic junction may be important factors to consider, especially for patients with high risk for nonunion.