Finite Element Study of a Lumbar Intervertebral Disc Nucleus Replacement Device

Abstract

Nucleus replacement technologies are a minimally invasive alternative to spinal fusion and total disc replacement that have the potential to reduce pain and restore motion for patients with degenerative disc disease. Finite element modeling can be used to determine the biomechanics associated with nucleus replacement technologies. The current study focuses on a new nucleus replacement device designed as a conforming silicone implant with an internal void. A validated finite element model of the human lumbar L3–L4 motion segment was developed and used to investigate the influence of the nucleus replacement device on spine biomechanics. In addition, the effect of device design changes on biomechanics was determined. A 3D, L3–L4 finite element model was constructed from medical imaging data. Models were created with the normal intact nucleus, the nucleus replacement device, and a solid silicone implant. Probabilistic analysis was performed on the normal model to provide quantitative validation metrics. Sensitivity analysis was performed on the silicone Shore A durometer of the device. Models were loaded under axial compression followed by flexion/extension, lateral bending, or axial rotation. Compressive displacement, endplate stresses, reaction moment, and annulus stresses were determined and compared between the different models. The novel nucleus replacement device resulted in similar compressive displacement, endplate stress, and annulus stress and slightly higher reaction moment compared with the normal nucleus. The solid implant resulted in decreased displacement, increased endplate stress, decreased annulus stress, and decreased reaction moment compared with the novel device. With increasing silicone durometer, compressive displacement decreased, endplate stress increased, reaction moment increased, and annulus stress decreased. Finite element analysis was used to show that the novel nucleus replacement device results in similar biomechanics compared with the normal intact nucleus.

Finite Element Analysis of a Bionate Ring-Shaped Customized Lumbar Disc Nucleus Prosthesis

“…Studying the characteristics and biomechanical results of our nucleus implant with FEM and the responses induced in nearby anatomical structures has been very useful to validate it, confirming the results obtained by other research groups with this same research tool. − The selected material seems to stand the needed biomechanical requirements with a negligible risk of permanent deformation or severe damage. The design appears to minimize the chances of subsidence or extrusion, and the central cavity seems to buffer axial compression loads, as reported by similarly shaped nucleus implants . The zygapophyseal joint and end plate pressures seem to recover sufficiently, but the transversal axis ( x - and y -axes) stresses on the annulus do not recover as well as desired.…”

“…The design appears to minimize the chances of subsidence or extrusion, and the central cavity seems to buffer axial compression loads, as reported by similarly shaped nucleus implants. 66 The zygapophyseal joint and end plate pressures seem to recover sufficiently, but the transversal axis ( x - and y -axes) stresses on the annulus do not recover as well as desired. A compact design with the same material would probably solve this problem, but this would be at the price of higher subsidence and extrusion risk, as already seen in other designs.…”

Extracellular Matrix From Decellularized Wharton’s Jelly Improves the Behavior of Cells From Degenerated Intervertebral Disc

“…In all its anatomical and functional complexity starting from the nucleus pulposus (NP, highly hydrophilic, rich of proteoglycans and collagen, with shock absorbing function), up to the annulus (AF, lamellar fibrocartilaginous tissue, with containment function) and cartilaginous endplates (a more rigid tissue acting as interface between disc and vertebrae), the IVD is attracting considerable interest from the scientists involved in tissue engineering field (Buckley et al, 2018;Farrugia et al, 2019;Tendulkar et al, 2019). In particular, several studies aim at developing innovative bio-inspired scaffolds, in order to counteract extracellular matrix (ECM) loss following degeneration/inflammation, and support functional recovery by endogenous damaged microenvironment (Coogan et al, 2016;Van Uden et al, 2017;Gullbrand et al, 2018). In this scenario, decellularized ECM deriving from autologous or non-autologous tissues represents an important advance in this field, as ideal system to deliver chemokines and growth factors, and provides adequate biomechanical microarchitecture also in the damaged IVD microenvironment (D'Este et al, 2018;Hensley et al, 2018;Liu et al, 2019;Ventre et al, 2019;Zhao et al, 2019).…”

Bionate Lumbar Disc Nucleus Prosthesis: Biomechanical Studies in Cadaveric Human Spines

“…Implants with an uneven load distribution have a higher subsidence risk, which is minimized in those with a central void cavity . Without this space, implants are stiffer and apply higher stresses on the adjacent endplates .…”