Methods Conclusion References Introduction Results Degenerative adult scoliosis results from age related changes leading to segmental instability, deformity and stenosis.[1] Spinal fusion is a standard method of surgical treatment for deformity.[2] Loss of native lumbar lordosis, abnormal loading and increased mobility in adjacent segments, may alone or in combination explain the development of adjacent level deterioration.[3] Finite element (FE) model studies have made important contributions to the understanding of functional biomechanics of the lumbar spine.[4] In comparison to in vitro or in vivo approaches, computational methods eliminate the issues with cadaver use, animal use and clinical human studies, in addition to being cost efficient, time efficient, and an accurate surrogate.[5] The purpose of this study was to develop a finite element model of a lumbar scoliotic spine, and investigate the effect of adjacent load transfer before and after fusion surgery. Two three-dimensional nonlinear finite element models of the lumbosacral spine were created from a 73-year old male subject’s pre and post scoliosis surgery CT scans (Fig. 1). Pedicle screws and rods were implanted during surgery at the L 2 to S 1 levels. The FE spine models were developed encompassing the T 12 to S 1 levels, along with the screws and rods for the post surgery model (Fig.2). 3D Slicer software was used to generate the outer shell virtual model of each individual vertebrate and disc. This was followed by a smoothing process to smooth these outer surfaces and fill in holes using Geomagic Studio software. These modified virtual models from T 12 to S 1 were imported into Truegrid and Hyperworks software to form 3D solids and these solids were meshed. Finally these meshed models were input into LS-DYNA for FE analysis under different loading conditions. For the analysis the S 1 level of the model was fixed. Seven ligaments and local muscle forces were added to this model.[6] A 500N compressive follower load and six different follower moments were applied to the T 12 level of this model: (1) flexion bending moment; (2) extension bending moment; (3) right lateral bending moment; (4) left lateral bending moment; (5) right axial rotation moment; and (6) left axial rotation moment. The compressive follower load was applied to represent the subject’s upper body weight. The six types of bending moment represent the six movements of the spine. The following values for pre- and post-surgery were compared for each load condition: intradiscal pressure and intersegmental rotation (flexion, extension, lateral bending, and axial rotation) at the L 1-2 level. With this study we were able to develop a finite element model of a lumbar scoliotic spine, and investigate the effect adjacent load transfer before and after fusion surgery. The results of this study will help define the variables contributing to adjacent level deterioration in the clinical environment. With this information a surgeon can plan the most appropriate surgical strategy pre surgery to prevent mid and long term adverse outcomes associated with adjacent level deterioration. The extent of intersegmental rotation in degrees and the extent of the intradiscal pressure at the L 1-2 level post surgery increased or stayed the same under the six loading conditions compared to the pre surgery condition (Fig. 3, Table 1). The post surgery pressure contours on the L 1-2 intervertebral disc varied with the different applied moments for the pre-and post-surgery (Table 1). 1. Kotwal S. HSS J 7(3), 257-64, 2011. 2. Kuklo TR, Spine 31(19), S132-8, 2006. 3. Barrey C, et al. World J Orthop 6(1), 117-26, 2015. 4. Dreischarf M, et al. J Biomech 47(8), 1757-66, 2014. 5. Bloemker KH, et al. Open Biomed Eng J 6, 33-41, 2012. 6. Rohlmann A, et al. J Biomech 39, 2484-90, 2006. Pre and post scoliosis fusion surgery scans. Figure 1. Figure 2. Figure 3. Pre and post fusion surgery intersegmental rotation of scoliosis spine at the L 1-2 level. Pre and post fusion surgery finite element models of scoliosis spine from T 12 -S 1 level with pedicle screws and rods at L 2 -S 1 . Flexion Extension Right Bending Left Bending Right Rotation Left Rotation Pre intersegmental rotation (Degree) -4.347 3.984 1.937 -1.824 -2.547 2.965 Post intersegmental rotation (Degree) -5.154 4.427 2.122 -1.7795 -2.324 2.837 Pre intradiscal pressure (Mpa) 1.486 0.809 0.435 0.438 0.324 0.387 Post intradiscal pressure (Mpa) 1.548 0.633 0.525 0.453 0.274 0.436 Table1. Intersegmental rotation and intradiscal pressure at level L 1-2 follower by 500N compressive load and six different types of moments. Figure 2. -6 -4 -2 0 2 4 6 Pre Post Intersegmental Rotation (Degree) Extension Right Bending Right Rotation Flexion Left Bending Left Rotation Finite Element-Based Adjacent Level Intersegmental Rotation and Intradiscal Pressure Analysis after Lumbar Fusion for Scoliosis 1 Ram Haddas, 2 Ming Xu, 3 Isador H. Lieberman, 2 Brandon J. Snailer, and 2 James Yang 1 Texas Back Institute Research Foundation, Plano, TX, USA 2 Texas Tech University, Lubbock, TX, USA 3 Texas Back Institute, Plano, TX, USA