Screw Loosening in Posterior Spine Fusion: Prevalence and Risk Factors.

Abstract

Study Design:Retrospective cohort study.Objective:Screw loosening in spinal fusion is poorly defined. Accordingly, its prevalence rates range from 1% to 60%, and its risk factors remain undefined. The goal of this study was to assess the prevalence of screw loosening, according to precise definitions, and to identify factors associated with it.Methods:We retrospectively reviewed records for 166 patients who underwent a posterior spinal fusion in our institution between 2011 and 2016. We recorded demographic data, osteoporosis, pelvic balance, surgery-related information, and postoperative radiographic data at a minimum follow-up of 6 months. Univariable and multivariable logistic regression models were used. Significance was defined by P < .05.Results:When loosening was defined by partial pull-out, its prevalence was 9.6% (95% CI 5.6-15); thoracic localization, the use of CrCo (chromium-cobalt) rods, osteoporosis, PI/LL (pelvic incidence/lumbar lordosis) mismatch (preoperative), and frontal imbalance (preoperative) were significant risk factors. When loosening was defined by osteolysis (radiolucent rim) >1 mm around at least 1 screw, its prevalence was 40.4% (95% CI 33-48) and age, scoliosis as indication for fusion, ASA (American Society of Anesthesiologists) 2 or 3, the use of CrCo rods, more than 5 levels fused, no circumferential arthrodesis, postoperative bracing, and sacrum or ilium as the inferior level of instrumentation were also significant risk factors.Conclusions:A clear definition of screw loosening seems essential for a useful analysis of the literature. Osteoporosis, sagittal imbalance, and rigid material appear to be risk factors, regardless of the definition.