Biomechanical role of osteoporosis affects the incidence of adjacent segment disease after percutaneous transforaminal endoscopic discectomy

Abstract

Study design Variation in the biomechanical characteristics of intervertebral discs adjacent to the segment disc after undergoing percutaneous transforaminal endoscopic discectomy (PTED) in models with normal and abnormal bone mineral density (BMD) was estimated using the finite element method. Objective The study investigated the change in the incidence of adjacent segment disease (ASD) after PTED in patients without and with osteoporosis. Backgrounds PTED has been widely used for treating lumbar disc herniation (LDH); changes in BMD will affect biomechanical characteristics, possibly leading to changes in the incidence of ASD after PTED. However, this issue remains largely unclear. Methods A non-linear, lumbosacral finite element model was reconstructed based on imaging data and validated using compared values computed by the current model from published and well-validated, in vitro biomechanical experiment studies. Corresponding PTED models with normal and abnormal BMDs were also reconstructed. Shear and von Mises stresses on the annulus fibrosis, the von Mises stress on the endplates in L5–S1 segment discs, and the total deformation of current lumbosacral models were computed in different body positions by changing loading conditions, including flexion, extension, left and right lateral bending, and axial rotation. Results In most loading conditions, biomechanical characteristics of the lumbosacral segment discs with normal BMDs after PTED slightly increased. However, in the PTED model with osteoporosis, most of the biomechanical characteristics dramatically increased. Conclusion Osteoporosis leads to the deterioration of biomechanical characteristics in the adjacent segment disc after PTED; this variation may also result in an increase in the incidence of ASD. However, further studies on the interactions between pathological changes are warranted.

Indications Selection for Surgeons Training in the Translaminar Percutaneous Endoscopic Discectomy Based on Finite Element Analysis

“…FEA models from L3 to S1 were constructed by standard curves. Bone structures include cortical, cancellous, and posterior structures reconstructed in our previous studies which were used as the templates for model construction [8,9,24]. Different parts of the templates were layered, and the outline in each layer was traced by standard curves.…”

“…In comparison with traditional open posterior surgery, PED should decrease the risk of adjacent segment disease (ASD) which was partly caused by a wide range of postoperative paraspinal muscle atrophy and epidural adhesion [2][3][4]. According to the literature, PED could nonetheless lead to biomechanical deterioration, the most important factor in the development of ASD [5][6][7][8][9].…”

Measurement and calibration of the nucleus position and its cross-sectional area ratio to increase the accuracy of finite element analysis

“…Finally, we can only de ne the relative nucleus position as being 'slightly posterior' to the centre of the disc, such that the lowest ACC of our model was lower than 70%, which needs to be improved further, even though the model validation process was veri ed in our previously published studies. Therefore, the calibration of the relative nucleus position and the investigation of a reliable ratio to de ne the above indicators are vital for improving the ACC of FEA, a widely used research method in the investigation of pathogenesis of DDD and optimization of spine surgical methods [6,9,13,27,33].…”

Measurement and calibration of the nucleus position and its cross-sectional area ratio to increase the accuracy of finite element analysis

“…Six different ligaments and a capsule of facet joints were constructed during the FEA preprocessing phase ( Fig. 4) [11,23,24]. The de nition of the relative nucleus position and its cross-sectional area ratio were con rmed according to P1 and P2, and the outer contour of the nucleus was obtained using the same ratio reduction as that of the disc contour to ensure that the intervertebral disc and nucleus have the same central point, for easy adjustment during the calibration process.…”

“…4), with smaller sizes (mesh re nement) being used in areas that experienced serious mesh distortion, and the cartilage-cartilage contact was de ned as frictionless [4,15,25]. Material properties of current models was de ned in consistent with our published studies [10,23,24]. Six degrees of freedom were rigidly xed under the inferior of L5, and moments were applied to the superior of L4 [13,14].…”