Abstract
Total disc replacement using tissue‐engineered intervertebral discs (TE‐IVDs) may offer a biological alternative to treat radiculopathy caused by disc degeneration. A composite TE‐IVD was previously developed and evaluated in rat tail and beagle cervical spine models in vivo. Although cell viability and tissue integration into host tissue were promising, significant implant displacement occurred at multiple spinal levels. The goal of the present study was to assess the effects of a resorbable plating system on the stiffness of motion segments and stability of tissue‐engineered implants subjected to axial compression. Canine motion segments from levels C2/C3 to C5/C6 were assessed as intact (CTRL), after discectomy (Dx), with an implanted TE‐IVD only (PLATE−), and with a TE‐IVD combined with an attached resorbable plate (PLATE+). Segments under PLATE+ conditions fully restored separation between endplates and showed significantly higher compressive stiffness than segments under PLATE− conditions. Plated segments partially restored more than 25% of the CTRL motion segment stiffness. Plate attachment also prevented implant extrusion from the disc space at 50% compressive strain, and this effect was more significant in segments from levels C3/C4 when compared to segments from level C5/C6. These results suggest that stabilization of motion segments via resorbable plating assists TE‐IVD retention in the disc space while allowing the opportunity for implants to fully integrate into the host tissue and achieve optimal restoration of spine biomechanics.
Highlights
Intervertebral disc (IVD) degeneration is known to alter the stability and biomechanics of cervical spine motion segments while decreasing the foraminal canal through which nerves stem from the spinal cord, in the most severe cases
We observed that all tissue-engineered intervertebral discs (TE-IVDs) at the C3/C4 level remained stable in the canine spine in vivo, while all TE-IVDs implanted at C5/C6 were displaced likely due to variations in size and angle of the VBs.[15]. Based on this previous work, we have identified two main challenges contributing to segment instability after placement of TE-IVDs: (1) mechanical robustness within the motion segment is limited because the implant needs to be immature to promote integration; (2) vertebral anatomy of motion segments varies by level and is suspected to affect the stability of implantation, which results in implant migration out of the disc space
We tested the hypothesis that resorbable plating improved stiffness of canine cervical spine motion segments in vitro and prevented the extrusion of implanted TE-IVDs from the disc space
Summary
Intervertebral disc (IVD) degeneration is known to alter the stability and biomechanics of cervical spine motion segments while decreasing the foraminal canal through which nerves stem from the spinal cord, in the most severe cases. Axial dynamic distraction using an external fixator alone and in combination with cell therapy has been shown to promote disc repair in rabbit IVDs.[17,18,19] To achieve IVD implant retention and prevent collapse of the disc space, external fixation of the vertebral bodies (VBs) has been shown to provide stability in rodent caudal spines.[20,21] the disc space height was maintained in these animal models, the implants were not exposed to physiologic loading, which was integral for TE-IVD maturation, integration to host tissue, and restoration of mechanical function. The PLGA in this commercially available stabilization system has been well characterized for its biocompatibility and resorption kinetics, and is FDA approved for in vivo reconstructive procedures To address these shortcomings, we asked whether TE-IVD implantation assisted by a resorbable plating system restores motion segment stiffness and prevent implant extrusion under axial compression, thereby improving overall stability of the treated segment. Our objectives with this study were to evaluate the restoration of the compressive mechanics of motion segments with a combined treatment approach of TE-IVD implanted with a PLGA fixation system and identify the ability of these resorbable plates to prevent implant extrusion
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