Contribution of Lateral Decubitus Positioning and Cable Tensioning on Immediate Correction in Anterior Vertebral Body Growth Modulation

Study design: Computational simulation of lateral decubitus and anterior vertebral body growth modulation (AVBGM).

Objectives: To biomechanically evaluate lateral decubitus and cable tensioning contributions on intra- and postoperative correction.

Summary of background data: AVBGM is a compression-based fusionless procedure to treat progressive pediatric scoliosis. During surgery, the patient is positioned in lateral decubitus, which reduces spinal curves. The deformity is further corrected with the application of compression by cable tensioning. Predicting postoperative correction following AVBGM installation remains difficult.

Methods: Twenty pediatric scoliotic patients instrumented with AVBGM were recruited. Three-dimensional (3D) reconstructions obtained from calibrated biplanar radiographs were used to generate a personalized finite element model. Intraoperative lateral decubitus position and installation of AVBGM were simulated to evaluate the intraoperative positioning and cable tensioning (100 / 150 / 200 N) relative contribution on intra- and postoperative correction.

Results: Average Cobb angles prior to surgery were 56° ± 10° (thoracic) and 38° ± 8° (lumbar). Simulated presenting growth plate's stresses were of 0.86 MPa (concave side) and 0.02 MPa (convex side). The simulated lateral decubitus reduced Cobb angles on average by 30% (thoracic) and 18% (lumbar). Cable tensioning supplementary contribution on intraoperative spinal correction was of 15%, 18%, and 24% (thoracic) for 100, 150, and 200 N, respectively. Simulated Cobb angles for the postoperative standing position were 39°, 37°, and 33° (thoracic) and 30°, 29°, and 28° (lumbar), respectively, whereas growth plate's stresses were of 0.54, 0.53, and 0.51 MPa (concave side) and 0.36, 0.53, and 0.68 MPa (convex side) for the three tensions.

Conclusion: The majority of curve correction was achieved by lateral decubitus positioning. The main role of the cable was to apply supplemental periapical correction and secure the intraoperative positioning correction. Increases in cable tensioning furthermore rebalanced initially asymmetric compressive stresses. This study could help improve the design of AVBGM by understanding the contributions of the surgical procedure components to the overall correction achieved.

Level of evidence: Level III.