Three-Dimensional Computed Tomography Analysis of Spinal Canal Length Increase After Surgery for Adolescent Idiopathic Scoliosis: A Multicenter Study

Abstract

Background: The most severe complication after surgery for adolescent idiopathic scoliosis is spinal cord injury. There is a relationship between corrective surgery and subsequent elongation of the spinal canal. We sought to investigate which factors are involved in this phenomenon.

Methods: Seventy-seven patients with adolescent idiopathic scoliosis (49 with Lenke type 1 and 28 with type 2) who underwent spinal correction surgery were included. The mean patient age at surgery was 14.2 years (range, 11 to 20 years). The spines of all patients were fused within the range of T2 to L2, and computed tomography (CT) data were retrospectively collected. We measured the preoperative and postoperative lengths of the spinal canal from T2 to L2 using 3-dimensional (3D) CT-based imaging software. We also examined the association between the change in T2-L2 spinal canal length and the radiographic parameters.

Results: The length of the spinal canal from T2 to L2 was increased by a mean of 8.5 mm in the patients with Lenke type 1, 12.7 mm in those with type 2, and 10.1 mm overall. Elongation was positively associated with the preoperative main thoracic Cobb angle in both the type-1 group (R = 0.43, p < 0.005) and the type-2 group (R = 0.77, p < 0.000001). The greatest elongation was observed in the periapical vertebral levels of the main thoracic curves.

Conclusions: Corrective surgery for adolescent idiopathic scoliosis elongated the spinal canal. The preoperative proximal, main thoracic, and thoracolumbar/lumbar Cobb angles are moderate predictors of postoperative spinal canal length after scoliosis surgery.

Clinical relevance: It is important to understand how much the spinal canal is elongated after surgery to lessen the risk of intraoperative and postoperative neurological complications.

Fig. 1

Figs. 1-A, 1-B, and 1-C Methodology for the assessment of spinal canal length. Fig. 1-A The center of the spinal canal is represented by the black dot on the axial CT image. Fig. 1-B The dots indicate the midpoint between the pedicles at each vertebra. The spinal canal length was calculated by adding the distances between all dots. Fig. 1-C Delta T2-L2 spinal canal length was calculated by subtracting the preoperative spinal canal length from the postoperative spinal canal length.

Fig. 2

Figs. 2-A, 2-B, and 2-C The changes in spinal canal length in each of the 4 subsegments, T2-T5, T5-T8, T8-T11, and T11-L2. *P < 0.05, Tukey-Kramer post-hoc test. The bars and error bars denote the means and SDs. Fig. 2-A Overall data (n = 77). Fig. 2-B Single-thoracic-curve group (n = 49). Fig. 2-C Double-thoracic-curve group (n = 28).

Fig. 3

Figs. 3-A, 3-B, and 3-C Associations between the preoperative major thoracic Cobb angle and delta T2-L2 spinal canal length. The Pearson correlation test was used. Fig. 3-A Single-thoracic-curve group (n = 49). Fig. 3-B Double-thoracic-curve group (n = 28). Fig. 3-C Overall data (n = 77).