Biomechanical Behavior of a New Nucleus Prosthesis Made of Knitted Titanium Filaments

Abstract

BackgroundOne of the greatest challenges in the development of a nucleus prosthesis is to minimize the risk of implant expulsion. At the same time, the physiological flexibility, compressive behavior, and height of the disc should be restored. In this biomechanical in vitro study we investigated the ability of a new nucleus prosthesis made of knitted titanium filaments to meet these challenges.MethodsFlexibility, axial deformation, and height of six bovine lumbar spine segments were measured in the intact condition, after implantation of the new prosthesis, and during and after complex cyclic loading (100,000 cycles). For this purpose, six new prostheses preformed according to the shape of the bovine nucleus pulposus were manufactured. Flexibility was tested in the three main planes under pure moment loads of 7.5 Nm. Axial deformation was measured under application of an axial force of 1000 N. Radiographs taken before and after cyclic testing were used to assess implant migration and expulsion.ResultsIn lateral bending, the intact range of motion (RoM) could almost be restored after implantation. However, in axial rotation, the RoM increased slightly with the implant. This was also the case in extension, with an increase from -2.9° to -6.4°, whereas in flexion, RoM decreased from 4.3° to 3.2°. In all loading planes, cyclic loading caused the RoM to increase asymptotically by 0.1° to 1.8°. The axial deformation of the specimens was nearly equivalent in all tested states, as was their height. Cyclic loading did not cause implant expulsion.ConclusionsIn this feasibility study, the new knitted nucleus prosthesis showed promising results in segmental flexibility, axial deformability, height, and implant expulsion. However, further study is needed for other factors, such as wear and fatigue behavior.

Nucleus pulposus replacement and regeneration/repair technologies: Present status and future prospects

“…The median value of AD was the same as that obtained immediately after implantation but, with cyclic loading, it decreased by about 33% (relative to the intact case) 63. The height change was the same as that obtained immediately after implantation but, with cyclic loading, it increased by a small amount (relative to the intact case) 63…”

“…Over the years, there have been many reports on a large number of these devices,28, 29, 31 32, 53‐68. but, in this review, reference is made to a sample of those devices that have received the most attention.…”

“…When implanted in bovine lumbar spines (L2‐L3 and L4‐L5 segments), the axial deformability (AD) and height of the construct were measured after quasi‐static loading (increased from 100 to 1000 N) as well as after the application of a complex cycling loading cycle (axial force of 100–600 N, at 5 Hz, that created an additional bending moment ranging from 3 to 18 Nm), while the construct was being continuously rotated around its longitudinal axis at 360° min −1 63. The median value of AD was the same as that obtained immediately after implantation but, with cyclic loading, it decreased by about 33% (relative to the intact case) 63. The height change was the same as that obtained immediately after implantation but, with cyclic loading, it increased by a small amount (relative to the intact case) 63…”

Characterisation of porous knitted titanium for replacement of intervertebral disc nucleus pulposus

“…Previously, Kettler et al . 13 in their study reported that this unique knitted titanium scaffold possessed adequate biomechanical properties and showed low migration tendency, thereby restoring the physiological axial deformability. Further, we have demonstrated that the knitted scaffold enable the cell attachment and promote cell proliferation 14 .…”

A pedicle screw system and a lamina hook system provide similar primary and long-term stability: a biomechanical in vitro study with quasi-static and dynamic loading conditions

“…The cyclic test was performed using a well-established dynamic test set-up, which has been used in several other experiments, e.g., to compare vertebro-and kyphoplasty methods jetzt [38], to provoke extrusion of nucleus implants jetzt [39], to test annulus sealing implants [40] or to produce an experimental herniation [41]. This is the first time this test set-up was used for bi-segmental fixation system to provoke an implant loosening.…”