Characteristics of Sagittal Alignment in Patients with Severe and Rigid Scoliosis

OBJECTIVE: There has been increasing concern about the importance of sagittal alignment in the evaluation and treatment of spinal scoliosis. However, recent studies have only focused on patients with mild to moderate scoliosis. To date, little is known about the sagittal alignment in patients with severe and rigid scoliosis (SRS). This study was performed to evaluate the sagittal alignment in patients with SRS, and to analyze how it was altered after corrective surgery. METHODS: In this retrospective cohort study, we included 58 patients with SRS who underwent surgery from January 2015 to April 2020. Preoperative and postoperative radiographs were reviewed, and the sagittal parameters mainly included thoracic kyphosis (TK), lumbar lordosis (LL), pelvic incidence (PI), pelvic tilt (PT), sacrum slope (SS), and sagittal vertical axis (SVA). The sagittal balance state was evaluated according to whether the PI minus the LL (PI‐LL) was less than 9°, and the patients were divided into thoracic hyperkyphosis and normal groups based on whether the TK exceeded 40°. The Student's t test, Pearson's test, and Receiver operating characteristic (ROC) curve analysis were used to compare related parameters between the different groups. RESULTS: The mean follow‐up duration was 2.8 years. Preoperatively, the mean PI was 43.6 ± 9.4°, and the mean LL was 65.2 ± 13.9°. Sixty‐nine percent of patients showed sagittal imbalance, and they showed larger TK and LL values and smaller PI and SVA values than those with sagittal balance. Additionally, most patients (44/58) presented with thoracic hyperkyphosis; this group had smaller PI and SVA values than the normal patients. Patients with syringomyelia‐associated scoliosis were more likely to present with thoracic hyperkyphosis. The TK and LL values were significantly decreased, and 45% of patients with preoperative sagittal imbalance recovered after surgery. These patients had a larger PI (46.4 ± 9.0° vs 38.3 ± 8.8°, P = 0.003) and a smaller TK (25.5 ± 5.2° vs 36.3 ± 8.0°, P = 0.000) at the final follow‐up. CONCLUSION: Preoperative sagittal imbalance appears in the majority of SRS patients, accounting for approximately 69% of our cohort. Patients with small PI values or syringomyelia‐associated scoliosis were more likely to present with thoracic hyperkyphosis. Sagittal imbalance can generally be corrected by surgery, except in patients with a PI less than 39°. To achieve good postoperative sagittal alignment, we recommend controlling the TK to within 31°.