Patient and surgical predictors of 3D correction in posterior spinal fusion: a systematic review

Abstract

Background Restoration of three-dimensional (3D) alignment is critical in correcting patients with adolescent idiopathic scoliosis using posterior spinal fusion (PSF). However, current studies mostly rely on 2D radiographs, resulting in inaccurate assessment of surgical correction and underlying predictive factors. While 3D reconstruction of biplanar radiographs is a reliable and accurate tool for quantifying spinal deformity, no study has reviewed the current literature on its use in evaluating surgical prognosis. Purpose To summarize the current evidence on patient and surgical factors affecting sagittal alignment and curve correction after PSF based on 3D parameters derived from reconstruction of biplanar radiographs. Methods A comprehensive search was conducted by three independent investigators on Medline, PubMed, Web of Science, and Cochrane Library to obtain all published information on predictors of postoperative alignment and correction after PSF. Search items included "adolescent idiopathic scoliosis," "stereoradiography," "three-dimensional," "surgical,” and "correction." The inclusion and exclusion criteria were carefully defined to include clinical studies. Risk of bias was assessed with the Quality in Prognostic Studies tool, and level of evidence for each predictor was rated with the Grading of Recommendations, Assessment, Development, and Evaluations approach. 989 publications were identified, with 444 unique articles subjected to full-text screening. Ultimately, 41 articles were included. Results Strong predictors of better curve correction included preoperative normokyphosis (TK > 15°), a corresponding rod contour, intraoperative vertebral rotation and translation, and upper and lower instrumented vertebrae selected based on sagittal and axial inflection points. For example, for Lenke 1 patients with junctional vertebrae above L1, fusion to NV-1 (1 level above the neutral vertebra) achieved optimal curve correction while preserving motion segments. Pre-op coronal Cobb angle and axial rotation, distal junctional kyphosis, pelvic incidence, sacral slope, and type of instrument were identified as predictors with moderate evidence. For Lenke 1C patients, > 50% LIV rotation was found to increase spontaneous lumbar curve correction. Pre-op thoracolumbar apical translation and lumbar lordosis, Ponte osteotomies, and rod material were found to be predictors with low evidence. Conclusions Rod contouring and UIV/LIV selection should be based on preoperative 3D TK in order to achieve normal postoperative alignment. Specifically, Lenke 1 patients with high-lying rotations should be fused distally at NV-1, while hypokyphotic patients with large lumbar curves and truncal shift should be fused at NV to improve lumbar alignment. Lenke 1C curves should be corrected using > 50% LIV rotation counterclockwise to the lumbar rotation. Further investigation should compare surgical correction between pedicle-screw and hybrid constructs using matched cohorts. DJK and overbending rods are potential predictors of postoperative alignment.

Emerging Technologies within Spine Surgery

“…Low PI, low LL, and high pelvic tilt are associated with increased ASD incidence [24]. The correction of these parameters to within normal limits with expandable cages or hyperlordotic implants may improve patient-reported outcome measures (PROMs) [25][26][27][28].…”

A Novel Multiple Screw Distraction Reducer System in the Treatment of Scoliosis with a Severe Rib Hump

“…Idiopathic scoliosis is a complex three‐dimensional “coupling” of deformity, with the coronal translation, sagittal hyperkyphosis or hypokyphosis, and axial rotation. 22 Based on the coupled motions of the spine, three‐dimensional correction with DVR is a crucial component in scoliosis correction and has been reported to achieve excellent orthopaedic results. Previous studies presented 64%–73% correction in the coronal plane using DVR technology.…”

Rod Angulation Relationship with Thoracic Kyphosis after Adolescent Idiopathic Scoliosis Posterior Instrumentation

“…The difference observed between concave and convex rods serves as a stark reminder that scoliosis is a three-dimensional deformity. Both rods play distinct roles in the reduction process, and their bending is influenced by both the desired final spinal shape and the mechanical stresses encountered during reduction maneuvers [26,27].…”