The relationship between S1 screw loosening and postoperative outcome in patients with degenerative lumbar scoliosis

Background When choosing S1 as the lowest level of instrumentation, there are many complications may come out such as S1 screw loosening. Facing this problem, there has been various techniques for the protection of S1 screw including sacropelvic fixation, bicortical or tricortical insertion of S1 screw. Objective This study aimed to explore the risk factors for the S1 screw loosening, then to demonstrate the relationship between S1 screw loosening and postoperative outcome for patients with degenerative lumbar scoliosis (DLS). Methods Patients who underwent lumbosacral fixation for DLS were evaluated retrospectively. They were divided into two groups according to the S1 pedicle screw at the follow-up. Age, gender, bone mineral density, body mass index, history of smoking, the number of instrumented levels, comorbidities, complications and radiological parameters were collected. We established logistic regression analysis to determine independent risk factors for S1 screw loosening and multiple linear regression to identify whether S1 screw loosening would influence postoperative clinical outcome. Results S1 screw loosening rate was up to 41.0% (32/78). Patients were older in the S1 screw loosening group than those in the control group ( P < 0.05). Compared with the control group, the rate of osteoporosis was higher in screw loosening group than that in the control group ( P < 0.05). Older age and osteoporosis were independent risk factors for S1 screw loosening ( P < 0.05). In the screw loosening group, the rate of hypertension was higher than that in the control group ( P < 0.05). The relationship of S1 screw loosening and ODI was not significant in the multiple linear regression ( P > 0.05). The clinical outcome was similar in the S1 screw loosening group and control group ( P > 0.05). Conclusion Older age and osteoporosis are independent risk factors for the S1 screw loosening. Patients with complication of S1 screw loosening are not always along with worse clinical outcome. We should consider potential benefit, complications and medical cost when choosing the lowest instrumented vertebrae for patients with DLS.