Abstract
Objective:To investigate the biomechanical effects of osteoporosis on adjacent segments after posterior lumbar interbody fusion (PLIF).Methods:This study was designed and conducted in the Traumatology and Orthopedics Laboratory, School of Chinese Medicine, Jinan University, Guangzhou, China, between December 2019 and February 2020. A healthy finite element model of L3-S1 was developed along with one PLIF model and one PLIF with osteoporosis model. Based on a hybrid test method, the inferior surface of S1 was entirely fixed, and a preload of 400N combined with an adjusted moment was imposed on the superior surface of L3 in each model to simulate flexion, extension, lateral bending and axial rotation. The intradiscal pressure (IDP), shear stress on annulus fibrosus, and the range of motion (ROM) of L3-L4 and L5-S1 were calculated and compared.Results:In each direction, the highest value of IDP and shear stress on annulus fibrosus at L3-L4 and L5-S1 was found in the PLIF model, and the lowest value in the healthy model. The largest ROM at L4-L5 appeared in the healthy model, and the smallest value in the PLIF model in each direction. At L3-L4 and L5-S1, the highest ROM in most directions was found in the PLIF model, followed by the PLIF with osteoporosis model, and the lowest value in the healthy model.Conclusions:Osteoporosis can decrease IDP, shear stress on annulus fibrosus, and ROM at adjacent levels, and slow down the development of ASD after PLIF.
Highlights
Adjacent segmental degeneration (ASD) is a common complication after lumbar fusion
Compared with the Posterior lumbar interbody fusion (PLIF) with osteoporosis model, the intradiscal pressure at L3-L4 level in PLIF model increased by 7.61%, 1.66%, 8.05%, and 2.34%, and the value at L5-S1 level increased by 9.27%, 2.55%, 8.92%, and 2.77% in flexion, extension, lateral bending, and axial rotation, respectively (Fig.[2] and 3)
Many studies have confirmed that increased intradiscal pressure, shear stress on annulus fibrosus, and range of motion (ROM) of the lumbar spine are closely associated with ASD.[8,16,17,18]
Summary
Adjacent segmental degeneration (ASD) is a common complication after lumbar fusion. It was reported that the incidence of radiographic ASD ranged from 8 to 100%, and symptomatic ASD ranged from 5.2 to 18.5%.1. Many factors, such as normal aging process, increased body mass index, and female gender, have been reported to have influence on ASD, but biomechanical factors play a key role in its pathogenesis.[2] As a result of increased rigidity, lumbar fusion results in hypermobility and stress concentration at adjacent levels, and subsequently causes the occurrence of ASD.[2,3].
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