Biomechanical Analysis of Adjacent Segments after Spinal Fusion Surgery Using a Geometrically Parametric Patient-Specific Finite Element Model

Published: January 19, 2024

doi:

Yuming Wang, Qianyi Shen, Chang Liang, Yanzhu Shen, Xiangsheng Tang, Ping Yi

¹Department of Spine Surgery,China-Japan Friendship Hospital, ²College of Mechanical and Electrical Engineering,Beijing University of Chemical Technology

Summary

Here, we used a patient-specific finite element model to analyze the mechanical changes in adjacent segments after spinal fusion surgery. The results showed that fusion surgery reduced the overall motion of the lumbar spine but increased the load on and stress in adjacent segments, especially the proximal segment.

Abstract

This study aimed to perform a mechanical analysis of adjacent segments after spinal fusion surgery using a geometrically parametric patient-specific finite element model to elucidate the mechanism of adjacent segment degeneration (ASD), thereby providing theoretical evidence for early disease prevention. Fourteen parameters based on patient-specific spinal geometry were extracted from a patient’s preoperative computed tomography (CT) scan, and the relative positions of each spinal segment were determined using the image match method. A preoperative patient-specific model of the spine was established through the above method. The postoperative model after L4-L5 posterior lumbar interbody fusion (PLIF) surgery was constructed using the same method except that the lamina and intervertebral disc were removed, and a cage, 4 pedicle screws, and 2 connecting rods were inserted. Range of motion (ROM) and stress changes were determined by comparing the values of each anatomical structure between the preoperative and postoperative models. The overall ROM of the lumbar spine decreased after fusion, while the ROM, stress in the facet joints, and stress in the intervertebral disc of adjacent segments all increased. An analysis of the stress distribution in the annulus fibrosus, nucleus pulposus, and facet joints also showed that not only was the maximum stress in these tissues elevated, but the areas of moderate-to-high stress were also expanded. During torsion, the stress in the facet joints and annulus fibrosus of the proximal adjacent segment (L3-L4) increased to a larger extent than that in the distal adjacent segment (L5-S1). While fusion surgery causes an overall restriction of motion in the lumbar spine, it also causes more load sharing by the adjacent segments to compensate for the fused segment, thus increasing the risk of ASD. The proximal adjacent segment is more prone to degeneration than the distal adjacent segment after spinal fusion due to the significant increase in stress.

Introduction

Intervertebral spinal fusion surgery is the most commonly used surgical procedure for the treatment of degenerative diseases of the lumbar spine¹. An excellent outcome in the short-term period after surgery can be achieved for more than 90% of patients². However, the results of a long-term follow-up study revealed that some patients developed degeneration of segments adjacent to the fused segment³. Lumbar interbody fusion accelerates degenerative changes in adjacent segments, which is known as adjacent segment degeneration (ASD). According to the literature, the incidence of ASD diagnosed based on medical imaging examinations ranges from 36% to 84% five years after fusion surgery⁴, which could lead to symptoms such as radiating pain or intermittent claudication and possibly even the need for revision surgery. The mechanism of ASD remains unknown, but most researchers believe that biomechanical factors play an important role. Some have attributed ASD to increased range of motion (ROM) of the adjacent segments after surgery⁵^,⁶, some have attributed it to increased intradiscal pressure in the adjacent segments⁷^,⁸^,⁹, and others have attributed it to increased stress in the facet joints of the adjacent segments¹⁰.

Among the various methods used to study spinal biomechanics, finite element (FE) modeling is widely used because it is noninvasive, inexpensive, and reproducible. Some researchers¹¹^,¹²^,¹³ have established a 3D FE model of the whole lumbar spine (L1-L5) with data extracted from preoperative computed tomography (CT) scans, which made it possible to explore various aspects of spinal biomechanics, ranging from the response of the spine to different loading conditions¹⁴^,¹⁵ to the effects of different pathologies¹⁶ and the effects of relevant treatment modalities and techniques¹⁷. Although the above modeling method could provide output regarding the patient-specific geometry of the spine with a complex interface and a wealth of information otherwise unattainable from in vivo experiments, its clinical use has remained limited due to the time-consuming nature of the process, rendering the method available only for models based on one or a few subjects¹⁴. To address this problem, Nikkhoo et al.¹⁸ established a simplified L1-S1 lumbosacral model in which the geometry of the spine is controlled by parameters extracted from patients' preoperative image data, allowing patient-specific models to be automatically generated or updated according to the input parameters. The FE model based on this modeling method has been proven to have good validity. However, there were significant differences in the intradiscal pressure, mean stresses in the facet joints, and mean stresses in the annulus fibrosus compared with the previous CT-based reconstructed model. Another simplified spinal model was applied in a study by Ghezelbash et al.¹⁹, but this model differed greatly from the real geometry of the lumbar spine due to the cylindrical shape of the vertebrae and lack of structure regarding the posterior elements.

Therefore, in this study, we developed a geometrically parametric patient-specific FE model to achieve a more efficient modeling and analysis process with good validity. Then, we performed a mechanical analysis of adjacent segments after fusion surgery to elucidate the mechanism and provide theoretical evidence for the early prevention of ASD.

Protocol

The protocol was conducted in accordance with the Declaration of Helsinki, and the protocol was approved by the Institutional Review Board of the China-Japan Friendship Hospital. 1. Parametric modeling of lumbar spine geometry Extract the initial data (DICOM 3.0 format with a pixel size of 0.33 mm and a layer spacing of 1 mm) for modeling from a CT scan data set of an adult healthy male with no history of trauma, deformity or tumor of the spine (height 180 cm, weig…

Representative Results

Simulation results of the patient-specific model compared to previous literature results ROM of the intervertebral disc According to the experimental loading conditions of Guan et al.27, a pure bending moment load of 3.5 N∙m in different directions was applied at the loading point of the model to simulate the lumbar spine motion in flexion, extension, and lateral bending, and the ROM of each segment was measured and compared with the results of G…

Discussion

In this study, a geometrically parametric patient-specific FE model was established to analyze the biomechanical characteristics of the lumbar spine after PLIF surgery. The results showed that the stress in the facet joints and disc of the fused segment decreased significantly after PLIF surgery, indicating that PLIF could effectively strengthen the stability of the decompressed segment and delay further aggravation of the lesion. The overall mobility of the lumbar spine decreased after PLIF surgery, while the ROM, facet…

Divulgazioni

The authors have nothing to disclose.

Acknowledgements

This research did not receive any specific grants from funding agencies in the public, commercial, or not-for-profit sectors.

Materials

Abaqus	Dassault	https://www.3ds.com/products/simulia/abaqus	Finite element analysis
AutoCAD	Autodesk	https://www.autodesk.com/products/autocad/	An Engineering Computer Aided Design software used to measure the ROM of different vertebral segment
CT scan dataset	China Japan Friendship Hospital		Dataset of an adult healthy male with no history of trauma, deformity or tumor of the spine (height 180 cm, weight 68 kg).The raw data were stored in Dicom 3.0 format with a pixel size of 0.33 mm and a layer spacing of 1 mm.
Hypermesh 2019	Altair	https://altair.com/hypermesh/	Mesh generation
Mimics Research 21.0	Materialise	https://www.materialise.com/en/healthcare/mimics-innovation-suite/mimics	Model construction

Riferimenti

Guigui, P., Ferrero, E. Surgical treatment of degenerative spondylolisthesis. Orthop Traumatol Surg Res. 103 (1), S11-S20 (2017).
de Kunder, S. L., et al. Transforaminal lumbar interbody fusion (TLIF) versus posterior lumbar interbody fusion (PLIF) in lumbar spondylolisthesis: a systematic review and meta-analysis. Spine J. 17 (11), 1712-1721 (2017).
Li, D., et al. Topping-off surgery vs posterior lumbar interbody fusion for degenerative lumbar disease: a comparative study of clinical efficacy and adjacent segment degeneration. J Orthop Surg Res. 14 (1), 197 (2019).
Hashimoto, K., et al. Adjacent segment degeneration after fusion spinal surgery-a systematic review. Int Orthop. 43 (4), 987-993 (2019).
Spivak, J. M., et al. Segmental motion of cervical arthroplasty leads to decreased adjacent-level degeneration: Analysis of the 7-year postoperative results of a multicenter randomized controlled trial. Int J Spine Surg. 16 (1), 186-193 (2022).
Liang, W., et al. Biomechanical analysis of the reasonable cervical range of motion to prevent non-fusion segmental degeneration after single-level ACDF. Front Bioeng Biotechnol. 10, 918032 (2022).
Wang, B., et al. Biomechanical evaluation of anterior and posterior lumbar surgical approaches on the adjacent segment: a finite element analysis. Comput Methods Biomech Biomed Engin. 23 (14), 1109-1116 (2020).
Hua, W., et al. Biomechanical evaluation of adjacent segment degeneration after one- or two-level anterior cervical discectomy and fusion versus cervical disc arthroplasty: A finite element analysis. Comput Methods Programs Biomed. 189, 105352 (2020).
Jiang, S., Li, W. Biomechanical study of proximal adjacent segment degeneration after posterior lumbar interbody fusion and fixation: a finite element analysis. J Orthop Surg Res. 14 (1), 135 (2019).
Kim, J. Y., et al. Paraspinal muscle, facet joint, and disc problems: risk factors for adjacent segment degeneration after lumbar fusion. Spine J. 16 (7), 867-875 (2016).
Shirazi-Adl, A., Ahmed, A. M., Shrivastava, S. C. A finite element study of a lumbar motion segment subjected to pure sagittal plane moments. J Biomech. 19 (4), 331-350 (1986).
Shirazi-Adl, S. A., Shrivastava, S. C., Ahmed, A. M. Stress analysis of the lumbar disc-body unit in compression. A three-dimensional nonlinear finite element study. Spine (Phila Pa). 9 (2), 120-134 (1984).
Brekelmans, W. A., Poort, H. W., Slooff, T. J. A new method to analyse the mechanical behaviour of skeletal parts). Acta Orthop Scand. 43 (5), 301-317 (1972).
Dreischarf, M., et al. Comparison of eight published static finite element models of the intact lumbar spine: predictive power of models improves when combined together. J Biomech. 47 (8), 1757-1766 (2014).
Schmidt, H., et al. Response analysis of the lumbar spine during regular daily activities–a finite element analysis. J Biomech. 43 (10), 1849-1856 (2010).
Tischer, T., et al. Detailed pathological changes of human lumbar facet joints L1-L5 in elderly individuals. Eur Spine J. 15 (3), 308-315 (2006).
Zhang, L., et al. Biomechanical changes of adjacent and fixed segments through cortical bone trajectory screw fixation versus traditional trajectory screw fixation in the lumbar spine: A finite element analysis. World Neurosurg. 151, e447-e456 (2021).
Nikkhoo, M., et al. Development of a novel geometrically-parametric patient-specific finite element model to investigate the effects of the lumbar lordosis angle on fusion surgery. J Biomech. 102, 109722 (2020).
Ghezelbash, F., et al. Subject-specific biomechanics of trunk: musculoskeletal scaling, internal loads and intradiscal pressure estimation. Biomech Model Mechanobiol. 15 (6), 1699-1712 (2016).
Rayudu, N. M., et al. Patient-specific finite element modeling of the whole lumbar spine using clinical routine multi-detector computed tomography (MDCT) data-A pilot study. Biomedicines. 10 (7), 1567 (2022).
Ambati, D. V., et al. Bilateral pedicle screw fixation provides superior biomechanical stability in transforaminal lumbar interbody fusion: a finite element study. Spine J. 15 (8), 1812-1822 (2015).
Mahran, M., ELsabbagh, A., Negm, H. A comparison between different finite elements for elastic and aero-elastic analyses. J Adv Res. 8 (6), 635-648 (2017).
Kurutz, M., Oroszváry, L. Finite element analysis of weightbath hydrotraction treatment of degenerated lumbar spine segments in elastic phase. J Biomech. 43 (3), 433-441 (2010).
Schmidt, H., et al. Application of a calibration method provides more realistic results for a finite element model of a lumbar spinal segment. Clin Biomech. 22 (4), 377-384 (2007).
Lu, Y. M., Hutton, W. C., Gharpuray, V. M. Can variations in intervertebral disc height affect the mechanical function of the disc. Spine (Phila Pa). 21 (19), 2208-2216 (1996).
Weinhoffer, S. L., et al. Intradiscal pressure measurements above an instrumented fusion. A cadaveric study. Spine (Phila Pa). 20 (5), 526-531 (1995).
Guan, Y., et al. Moment-rotation responses of the human lumbosacral spinal column). J Biomech. 40 (9), 1975-1980 (2007).
Panjabi, M. M., et al. Mechanical behavior of the human lumbar and lumbosacral spine as shown by three-dimensional load-displacement curves. J Bone Joint Surg Am. 76 (3), 413-424 (1994).
Wilke, H., et al. Intradiscal pressure together with anthropometric data–a data set for the validation of models. Clin Biomech. 16, S111-S126 (2001).
Perez-Orribo, L., et al. Biomechanics of a posterior lumbar motion stabilizing device: In vitro comparison to intact and fused conditions. Spine (Phila Pa). 41 (2), E55-E63 (2016).
Schmoelz, W., et al. Biomechanical evaluation of a posterior non-fusion instrumentation of the lumbar spine. Eur Spine J. 21 (5), 939-945 (2012).
Shono, Y., et al. Stability of posterior spinal instrumentation and its effects on adjacent motion segments in the lumbosacral spine. Spine (Phila Pa). 23 (14), 1550-1558 (1998).
Ha, K. Y., et al. Effect of immobilization and configuration on lumbar adjacent-segment biomechanics. J Spinal Disord. 6 (2), 99-105 (1993).
Matsukawa, K., et al. Incidence and risk factors of adjacent cranial facet joint violation following pedicle screw insertion using cortical bone trajectory technique. Spine (Phila Pa). 41 (14), E851-E856 (2016).
Hilibrand, A. S., Robbins, M. Adjacent segment degeneration and adjacent segment disease: the consequences of spinal fusion. Spine J. 4, 190S-194S (2004).
Hwang, D. W., et al. Radiographic progression of degenerative lumbar scoliosis after short segment decompression and fusion. Asian Spine J. 3 (2), 58-65 (2009).
Chen, W. J., et al. Surgical treatment of adjacent instability after lumbar spine fusion. Spine (Phila Pa). 26 (22), E519-E524 (2001).
Cunningham, B. W., et al. The effect of spinal destabilization and instrumentation on lumbar intradiscal pressure: an in vitro biomechanical analysis. Spine (Phila Pa). 22 (22), 2655-2663 (1997).
Bashkuev, M., Reitmaier, S., Schmidt, H. Effect of disc degeneration on the mechanical behavior of the human lumbar spine: a probabilistic finite element study. Spine J. 18 (10), 1910-1920 (2018).
Nikkhoo, M., et al. Anatomical parameters alter the biomechanical responses of adjacent segments following lumbar fusion surgery: Personalized poroelastic finite element modelling investigations. Front Bioeng Biotechnol. 11, 1110752 (2023).