Neurosurgery Resident University of Pennsylvania Philadelphia, PA, US
Disclosure(s):
John D. Arena, MD: No financial relationships to disclose
Introduction: Surgical correction of adult spinal deformity (ASD) with long segment fusion can afford considerable improvement in quality of life. ASD correction, however, is associated with a high rate of post-operative complications including implant failure. Loosening of pelvic screw fixation may be identified on routine follow-up standing radiographs, the natural history and clinical significance of which warrant further consideration.
Methods: A single-institution retrospective cohort of 155 patients (68.5% female, mean age 64.1) who underwent thoracolumbosacral fusion with pelvic fixation for ASD was reviewed. Patients with a minimum two-year follow-up (median 3.6 years) were included. Standing upright radiographs were assessed for evidence of pelvic screw loosening. Surgical revision of spinal instrumentation served as the primary outcome. Logistic regression and Kaplan-Meier survival analyses were performed.
Results: All cases demonstrated distal construct pelvic fixation with 1 (13 cases, 8.4%), 2 (107 cases, 69.0%), 3 (10 cases, 6.5%) or 4 (25 cases, 16.1%) pelvic screws. Iliac screws were utilized in 129 (83.2%) cases, S2 Alar-Iliac (S2AI) screws in 7 (4.5%) cases, and combination of iliac and S2AI in 19 (12.3%) cases. 27 cases (17.4%) developed evidence of pelvic screw loosening. Kaplan-Meier analyses demonstrated cumulative incidence of pelvic loosening of 0.08 at one year, 0.11 at two years and 0.16 at three years following surgery. A greater proportion of cases with loosening were diagnosed with osteoporosis prior to surgery (29.6% vs 17.2%). Pelvic screw loosening was associated with significantly increased odds of eventual instrumentation revision surgery (Odds Ratio 2.87, 95% CI 1.18-6.99, p=0.02).
Conclusion : Pelvic screw loosening occurs frequently following ASD correction and can develop years following surgery. While pelvic screw loosening may reflect an incidental finding, it is associated with significantly increased odds of eventual instrumentation revision surgery. Identification of pelvic fixation loosening warrants increased attention and close surveillance in follow-up.