Optimization of a lumbar interspinous fixation device for the lumbar spine with degenerative disc disease

Abstract

Interspinous spacer devices used in interspinous fixation surgery remove soft tissues in the lumbar spine, such as ligaments and muscles and may cause degenerative diseases in adjacent segments its stiffness is higher than that of the lumbar spine. Therefore, this study aimed to structurally and kinematically optimize a lumbar interspinous fixation device (LIFD) using a full lumbar finite element model that allows for minimally invasive surgery, after which the normal behavior of the lumbar spine is not affected. The proposed healthy and degenerative lumbar spine models reflect the physiological characteristics of the lumbar spine in the human body. The optimum number of spring turns and spring wire diameter in the LIFD were selected as 3 mm and 2 turns, respectively—from a dynamic range of motion (ROM) perspective rather than a structural maximum stress perspective—by applying a 7.5 N∙m extension moment and 500 N follower load to the LIFD-inserted lumbar spine model. As the spring wire diameter in the LIFD increased, the maximum stress generated in the LIFD increased, and the ROM decreased. Further, as the number of spring turns decreased, both the maximum stress and ROM of the LIFD increased. When the optimized LIFD was inserted into a degenerative lumbar spine model with a degenerative disc, the facet joint force of the L3-L4 lumbar segment was reduced by 56%–98% in extension, lateral bending, and axial rotation. These results suggest that the optimized device can strengthen the stability of the lumbar spine that has undergone interspinous fixation surgery and reduce the risk of degenerative diseases at the adjacent lumbar segments.

Numerical Assessment of Interspinous Spacers for Lumbar Spine

“…Gazzeri reported, "The ISP analyses increase the risk of fracture of the spiny process". The prosthesis avoids Comparing the results with those of other researchers that have used the FEM to visualize the behavior of various ISP [32,[50][51][52][53][54], it is concluded that the results are satisfactory since, in these studies, the maximum forces are generated in the prosthesis and the deformations are reduced. Therefore, the prostheses end up providing excellent stability to the spine.…”

“…The model's validation was performed considering the behavior of the FEM model in relaxed standing without the ISP versus the loads and ROMs used by other researchers. In the literature, the forces employed in experiments and simulations vary from 220 N to 1200 N [32,[50][51][52][53]. The displacements coincide with other research [54].…”

Validation and Estimation of Obesity-Induced Intervertebral Disc Degeneration through Subject-Specific Finite Element Modelling of Functional Spinal Units

“…For the developed FSU, RoM was 5.17 • in flexion, 1.54 • in extension, 3.36 • in lateral bending, and 1.14 • in axial rotation. The present study was compared with previous in vivo studies [80][81][82][83], then it was compared with a mean of all FE studies, as well as the results of six other FE studies [69,74,[84][85][86][87], as combinedly reported by Dreischarf et al, 2014 [70,88]. It must be highlighted here that, despite the slight variation in RoM from the earlier published data, the median of all the data was taken for comparison of our results.…”