The change of Roussouly classification after posterior lumbar fusion surgery

Background: Roussouly classification is an important morphologic classification which can help to determine high local stress zones of the spine. Different lumbar morphologies of Roussouly type suggest different biomechanics leading to degenerative evolution. This study aimed both to describe the change of the Roussouly classification of the human spine after posterior lumbar fusion surgery and to explore the influencing factors of postoperative Roussouly type. Methods: The study is a retrospective case-control study on preoperative and postoperative Roussouly types. A total of 167 patients with lumbar degenerative disease who had undergone short-level transforaminal lumbar interbody fusion surgery between January 2014 and December 2017 in the Department of Orthopedic Surgery, First Affiliated Hospital, Air Force Medical University, were recruited. Preoperative and postoperative general data including gender, age, follow-up time, Oswestry disability index (ODI) score, visual analogue scale (VAS) score, diagnosis, and surgical segment were recorded. Clinical parameters including pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), lumbar lordosis (LL), thoracic kyphosis (TK), and sagittal vertical axis (SVA) were measured using Surgimap software, and the Roussouly classification was assessed. Results: This study included 86 male patients and 81 female patients with a mean age of 52.0 +/- 12.4 (14-88) years. The mean follow-up time for these patients was 11.5 +/- 6.9 months. The value of sagittal alignment parameters changed after the posterior lumbar fusion surgery, except for the PI value (P=0.591). Roussouly classification changed after surgery. The preoperative Roussouly values of preoperative PI, SS, and LL were significantly different in patients of 4 postoperative Roussouly types. Conclusions: The Roussouly classification changes after posterior lumbar fusion surgery. This change is independent of gender, age, follow-up time, and the number of surgical segments. The preoperative Roussouly type and PI value are essential in predicting one's postoperative Roussouly type.