Biomechanical and in vivo evaluation of experimental closure devices of the annulus fibrosus designed for a goat nucleus replacement model

Abstract

Promising strategies are being developed to replace or regenerate the herniated nucleus pulposus. However, clinical efficacy of these methods has still to be addressed, and the lack of appropriate annulus closure techniques is increasingly being recognised as a major limiting factor. In the current study, in vitro and in vivo evaluation of novel annulus closure devices (ACDs) was performed. These devices are intended to be used in adjunct to nucleus replacement therapies in an experimental goat study. After a standardised discectomy had been performed, different ACDs were implanted solely or in addition to a collagen nucleus replacement implant. Biomechanical effects and axial failure load were assessed in vitro and followed by in vivo evaluation in a goat model. On axial compression, the average axial failure load for ACDs with four barb rings was significantly higher compared to the implants with five barb rings. The increased range of flexion–extension and latero-flexion observed after discectomy were restored to the normal range after implantation of the implants. Positive findings with the four-ring ACD were confirmed in goats after a follow-up of 2 weeks in vivo. However, after 6 weeks most implants (n = 16) showed signs of destruction and displacement. Although there seemed to be a tendency towards better results when ACDs were placed in addition to the nucleus replacements, these differences were not statistically significant. Moreover, two endplate reactions extending into the subchondral bone were observed, most likely due to continuous friction between the ACD and the vertebrae. Although current results are encouraging first steps towards the development of an efficient ACD for animal models, further optimisation is necessary. Current results also show that one cannot rely on in vitro biomechanical studies with annulus closure techniques, and these should always be confirmed in vivo in a large animal model.

Enhancement of Energy Production of the Intervertebral Disc by the Implantation of Polyurethane Mass Transfer Devices

“…One could use a percutaneous procedure similar to a discogram to insert the PU mass transfer devices through the dorsal AF in discs demonstrating degeneration to attempt to arrest disc degeneration from nutrient loss. During daily living, the human lumbar spine withstands compressive loads of high magnitudes [63] which may cause migration and deformation of implanted devices [29]. In this study, no static or dynamic loading was applied to FSUs during 7 days of culture.…”

“…Recent studies have shown that several biomaterials implanted for closure of AF defects maintain the height and stability of the IVD [29–31]. Since there are ample nutrient supplies at the edges of AF due to blood supply, porous materials with high transport properties implanted in AF can be designed to facilitate transport of nutrients from the edge of AF into the NP region in order to promote cellular energy production.…”

Role of biomechanics in intervertebral disc degeneration and regenerative therapies: what needs repairing in the disc and what are promising biomaterials for its repair?

“…In-vivo testing of various suture techniques failed to restore healthy biomechanics better than no repair (151). Plug devices intended to retain NP fluid pressurization have failed due to mismatched compliance between the implant and surrounding tissue (152). Recently developed fibrin-genipin hydrogel adhesives with tuneable mechanical properties (Figure 6B) (153) may have the potential to fill these gaps without inducing stress concentrations in the surrounding tissue.…”

Mechanical restoration and failure analyses of a hydrogel and scaffold composite strategy for annulus fibrosus repair

“…The reduction in re-herniation rates was promising for a sutured AF repair, but no data was reported on disc height, biomechanical restoration of the motion segment, or MRI signal intensity providing no evidence that this technique would successfully prevent accelerated degeneration following discectomy procedures. An annulus closure plug had favorable biomechanical results in vitro but showed deformation and herniation after 6 weeks in an in vivo goat model [16]. Alternately, Barricaid is a device resembling a shield that is secured with an anchor into the adjacent inferior vertebral body to reduce the risk of tissue expulsion following a discectomy procedure (Intrinsic Therapeutics, Inc., Woburn, MA).…”