Introduction: Most surgery for AIS is performed via a posterior‐only approach with the advent of pedicle screw instrumentation. However, to establish spinal flexibility in rigid, severe curves and optimize correction, surgeons employ various posterior release techniques to derotate the spine and re‐establish thoracic kyphosis. The aim of this study was to perform sequential releases of the posterior elements and quantify the subsequent increase in rotational motion and kyphosis generation.
Methods: Seven fresh frozen human cadaver spines with ribs intact (T3‐L1) were thawed and dissected, avoiding disruption of spinal ligaments, facets and disks. The spines were fixed at T3 proximally and L1 distally and mounted on a 6 DOF spine simulator test frame. Load control protocol was used; an unconstrained pure moment of ±5Nm was used for axial rotation. A total of three load / unload cycles were performed for each sequential posterior element release. Range of motion (ROM) was measured using the Optitrak Certus (NDI, Inc. Watrerloo, Canada) motion analysis system. Markers were placed at T4, T5, T6, T7, T8, T9, T10, T11 and T12. The ROM for each release was compared with each other and with the intact specimen and normalized. Single factor ANOVA was run for different data groups at p<0.05.
Results: An interval increase of vertebral rotational motion and kyphosis generation was seen after each subsequent posterior element release compared to the intact specimen (see graph below). The most significant rotational motion increases were observed after the Ponte osteotomy and costotransversectomy; mean increases of 139% and 177% over the intact specimen (p<0.05), respectively. The middle segments (T7‐T9) displayed the largest motion differences and the smallest differences were seen at the ends of the specimens, adjacent to the potted vertebrae.
Conclusion: Posterior element releases, both ligamentous and bony, result in sequential increases in spinal flexibility, vertebral derotation and kyphosis generation. The most significant motion increases were observed after the Ponte osteotomy and costotransversectomy. These findings support the use of posterior releases to correct severe curvatures, axially derotate the apex and re‐establish thoracic kyphosis.
** JOHN H. MOE AWARD NOMINEE FOR BEST BASIC SCIENCE POSTER