What Are the Medium-term Reciprocal Changes in Cervical Sagittal Alignment After Posterior Correction for Lenke 5C Adolescent Idiopathic Scoliosis?

Abstract

Background: Abnormal cervical sagittal alignment (CSA), typically cervical kyphosis, is more common in patients with adolescent idiopathic scoliosis (AIS) than in teenagers without AIS. Changes in CSA after posterior spinal fusion for AIS have been observed and may be associated with patient-reported clinical outcomes and age-related cervical disc degeneration. Previous studies have shown inconsistent postoperative reciprocal changes in CSA in patients with single structural thoracolumbar/lumbar (TL/L) AIS (Lenke 5C classification). However, little is known about the medium-term reciprocal changes in CSA after selective posterior TL/L fusion surgery.

Questions/purposes: We sought to determine the following: (1) What proportion of patients with Lenke 5C AIS have abnormal CSA before surgery? (2) What were the changes in CSA after selective posterior TL/L fusion surgery in the overall Lenke 5C AIS cohort and in subgroups classified by thoracic kyphosis? (3) What global sagittal parameters were associated with CSA preoperatively and at the latest follow-up? (4) What is the correlation between CSA and Scoliosis Research Society Outcomes Questionnaire (SRS-22) scores?

Methods: We queried our institutional database and identified 186 patients diagnosed with Lenke 5C AIS who underwent selective posterior TL/L fusion surgery from April 2010 to February 2018. Of these, 13% (25) of patients were lost to follow-up before 5 years, and 8% (15) of patients were excluded based on exclusion criteria, leaving 79% (146) of patients for analysis in this retrospective study. During this period, we typically offered selective posterior TL/L fusion surgery to patients with Lenke 5C AIS when the main TL/L Cobb angle exceeded 35°. All patients who were offered surgery for this diagnosis opted to have the procedure. Briefly, the surgical procedure consisted of pedicle screw insertion, multiple-level Ponte osteotomy, and segmental direct vertebral body derotation to correct the deformity. Ninety percent (132 of 146) of the patients were female, with a mean ± SD age of 15 ± 2 years. The mean follow-up time was 7 ± 1 years. All patients had a single structural TL/L curve, with a mean preoperative main TL/L Cobb angle of 43° ± 9°. Radiologic measurements included coronal deformity parameters, cervical sagittal parameters, and global sagittal parameters. SRS-22 scores were used to evaluate clinical outcomes. The preoperative cervical sagittal parameters were analyzed to assess the abnormal CSA proportion. Cervical sagittal parameters were compared preoperatively, postoperatively, and at the latest final follow-up. Based on the degree of thoracic kyphosis, patients were classified into a hypokyphotic group (thoracic kyphosis < 20°) and a normokyphotic group (thoracic kyphosis ≥ 20°), with further comparison of CSA within subgroups. Multiple linear regression analysis was performed to assess the correlation between CSA and global sagittal parameters. Finally, the SRS-22 scores at the latest follow-up were compared between cervical lordosis (defined as CSA > 0°) and cervical kyphosis (defined as CSA < 0°).

Results: Fifty-eight percent (84 of 146) of patients with Lenke 5C AIS had cervical kyphosis before surgery. After selective posterior TL/L fusion surgery, we observed an increase in cervical lordosis (from 5° ± 13° before surgery to 2° ± 12°, mean difference 4° [95% confidence interval (CI) 2° to 5°]; p < 0.001), thoracic kyphosis (from 19° ± 9° before surgery to 28° ± 10°, mean difference -9° [95% CI -11° to -8°]; p < 0.001), and lumbar lordosis (from -48° ± 11° before surgery to -51° ± 14°, mean difference 3° [95% CI 1° to 6°]; p = 0.005) at 5 years of follow-up. Subgroup analysis revealed an increase in CSA in the hypokyphotic group, while no increase was observed in the normokyphotic group. At the preoperative stage, after controlling for potentially confounding variables such as the C2-7 sagittal vertical axis and lumbar lordosis, a correlation was observed between thoracic kyphosis (β = -1.27 [95% CI -1.50 to -1.03]; p < 0.001) and the preoperative CSA. At the latest follow-up, after controlling for potentially confounding variables such as thoracic kyphosis, a correlation was observed between global thoracic kyphosis (β = -0.46 [95% CI -0.85 to -0.08]; p = 0.02) and the follow-up CSA. When we compared patients with cervical kyphosis at the most recent follow-up to those with cervical lordosis, we found no between-group differences in SRS-22 scores between those groups.

Conclusion: In light of our findings, surgeons should pay particular attention to preoperative CSA in these patients. For patients with cervical kyphosis and cervical discomfort, if there is concurrent reduction in thoracic kyphosis, it can be communicated that both CSA and thoracic kyphosis are likely to improve postoperatively. Future studies should use more specific outcome measures to assess the correlation between CSA changes and patient-reported clinical outcomes.

Level of evidence: Level III, therapeutic study.