Cervical sagittal alignment and the impact of posterior spinal instrumented fusion in patients with Lenke type 1 adolescent idiopathic scoliosis

Background: Clinical decision making, preoperative planning, and surgical correction for adolescent idiopathic scoliosis (AIS) has traditionally focused on obtaining the maximum coronal plane correction to improve cosmesis and function. More recently, restoring sagittal alignment has also received increasing attention in AIS patients, correlating with positive health-related quality of life (HRQOL) outcomes in multiple studies. In this realm, cervical sagittal alignment (CSA) has also emerged as one of the variables that may correlate with clinical and functional outcomes in AIS patients undergoing surgical correction. Several studies have focused on studying the cervical sagittal plane parameters in patients with spinal deformity, while few have investigated the impact of surgical correction on CSA. In this study, we aimed to capture the baseline cervical sagittal characteristics and evaluate the changes in CSA in a cohort of AIS patients with Lenke type I curves following posterior spinal instrumented fusion (PSIF). Methods: We evaluated our longitudinal database of patients who had surgical correction for AIS between January 1, 2015 and September 1, 2017. The initial search yielded 270 patients. Next, the following inclusion criteria were applied to identify the study cohort: (I) patients who had Lenke type 1 curves, (II) patients with adequate pre-operative and post-operative radiographs (posterior-anterior and lateral), (III) patients who had a minimum radiographic follow-up of 6 months, and (IV) patients who were treated with the same standard rod instrumentation system. In addition, the following exclusion criteria were applied: (I) patients with neuromuscular disorders, (II) patients with prior spine surgery, and (III) those who received greater than Schwab-2 osteotomies. A total of 30 patients were included in our final analysis. The C2–C7 angle, C0–C2 angle, C2–C7 sagittal vertical axis (SVA), McGregor slope (McGS), and the T1 slope angle were measured preoperatively and at 6 months. A kyphotic measurement was assigned a negative value while positive values were used to describe lordotic measurements. Descriptive statistics and paired sample t-test were used to compare pre-and post-operative data with a cutoff P value of 0.05 to determine statistical significance. Results: Overall, CSA improved in most patients post-operatively, with 19/30 (63%) resulting in improved lordosis. Pre-operatively, mean C2–C7 cervical lordosis was −4.3°, which improved to −0.5° postoperatively (P=0.075), with a mean difference of 3.7°. Simultaneously, mean C0–C2, C2–C7 SVA, McGS, and T1 slope changed from 17° (range, −18° to 41°), 26.5 mm (range, 10 to 45 mm), 4° (range, −7.5° to 25°), and 17.4° (range, 1° to 42°) to 16° (range, 0° to 34.4°, mean difference =1.01°, and P=0.548), 28.2 mm (range, 9 to 57 mm, mean difference =2 mm, and P=0.244), 4.03°, (range, −7.8° to 25°, mean difference =0.16, and P=0.916), and 18° (range, 5.4° to 42°, mean difference =0.37, and P=0.761) (mean change of C2–C7 angle of 3.76°). Conclusions: This study demonstrated baseline cervical kyphosis and a trend towards cervical lordosis restoration in patients with AIS and a Lenke type 1 curve who underwent PSIF. This study adds to emerging evidence and, together with further studies, will help estimate the impact of PSIF on the cervical sagittal profile, the effect of CSA on patient reported outcomes, and ways to address cervical sagittal malalignment when undertaking the surgical correction for specific curve types in AIS.