A three-dimensional retrospective analysis of the evolution of spinal instrumentation for the correction of adolescent idiopathic scoliosis

Abstract

This is a clinical radiographic study, spanning over three decades, analyzing the three-dimensional (3-D) changes in spine geometry after corrective surgery for adolescent idiopathic scoliosis (AIS) using four generations of instrumentation systems. The objective of this study was to retrospectively evaluate the evolution of spinal instrumentation over time by measuring the 3-D changes of spinal shape before and after surgical correction of subjects with AIS using Harrington/Harrington-Luque (H/HL) instrumentation, original and recent generations of Cotrel-Dubousset Instrumentation (CDI) with rod rotation maneuvers, as well as third generation systems using thoracic pedicle screws and direct vertebral derotation (DVD) manoeuver in order to determine if the claims for improved 3-D correction from generation to next generation could be substantiated. The 3-D shape of the thoracic and lumbar spine was recorded from a pair of standing radiographs using a novel 3-D reconstruction technique from uncalibrated radiographs in 128 adolescents with AIS undergoing surgery by a posterior approach. Changes in coronal Cobb angles, kyphosis, lordosis, as well as in a series of 3-D parameters computed from the spine reconstructions before and after surgery were used to compare the four groups. Results demonstrate statistically significant differences (P = 0.05) between generations with regards to the correction of the coronal Cobb angle, and different loss of physiological lordosis. More importantly, significant differences in the 3-D correction of the spine based on the orientation of the planes of maximal curvature were observed (20/-6% H/HL vs. 39/39% CDI vs. 42/18% DVD for the thoracic/lumbar regions, respectively), confirming that recent CDI and third generation instrumentations coupled with DVD can bring the deformity significantly closer to the sagittal plane. An increased correction in apical vertebra axial rotation was observed with the DVD manoeuver (74%), while fewer notable differences were found between DVD and recent CDI systems in terms of 3-D correction. This is the first quantitative study to clearly demonstrate that the rod derotation and DVD maneuvers can significantly improve 3-D correction of scoliotic deformities, thereby supporting the transition towards these more elaborate and costly instrumentation technologies in terms of 3-D assessment.

Fig. 1

Identified anatomical landmarks (pedicle tips and endplate centers) used by the self-calibration algorithm

Fig. 2

Example of a 3-D reconstruction of the spine with corresponding radiographs for an adolescent with scoliosis before surgery (Pre-op) and after surgery using Harrington/Harrington-Luque instrumentation (Post-op). The model can be viewed in the coronal plane, sagittal plane, apical view (along Z axis), or planes of maximum curvature

Fig. 3

Example of a 3-D parameteric representation of the spine with corresponding radiographs for an adolescent with scoliosis before surgery (Pre-op) and after surgery using original Cotrel-Dubousset instrumentation (Post-op)

Fig. 4

Example of a 3-D parameteric representation of the spine with corresponding radiographs for an adolescent with scoliosis before surgery (Pre-op) and after surgery using recent Cotrel-Dubousset instrumentation (Post-op)

Fig. 5

Graphical representation of 3-D clinical indices used for the evaluation of spinal deformities. a Computer Cobb angle in the coronal plane, b Kyphosis and lordosis in the sagittal plane, c axial rotation of the apical vertebra

Fig. 6

a Determining the contrained plane passing through the end vertebrae. b Projection of the maximal curvature plane in 3-D view. c Plane of maximal curvature in the top view

Fig. 7

Top view of the spine (view along spinal axis) illustrating orientation of planes of maximum deformity (θ) for a case exhibiting severe scoliosis (left) and a case exhibiting no scoliosis (right). In the normal case, the orientation of the planes of maximum curvature is close to 0° from the sagittal plane

Fig. 8

Statistical model of spine shape deformations of cases in Group D (Direct Vertebral Derotation) instrumented up to L2 (Top), and lower than L2 (Bottom). From left to right: mean shapes, 3-D rotation and 3-D translation covariance

Fig. 9

Evolution of spinal instrumentation. a Percentage (%) of correction for coronal Cobb angles; b Percentage (%) of decrease in kyphosis and lordosis; c Percentage (%) of correction in 3-D measurements including plane of maximum curvature (PMC)

Fig. 10

Top views of planes of maximal curvature for typical pre- and post-op cases in Group A (Harrington/Harrington-Luque), Group B (original Cotrel-Dubousset Instrumentation), Group C (recent generations of Cotrel-Dubousset Instrumentation), Group D (Direct Vertebral Derotation)