In Vivo Total Disc Replacement using Tissue-Engineered Intervertebral Discs in a Canine Model

Abstract

Introduction Disc degeneration in the cervical spine is a prevalent clinical predicament often requiring surgery. Anterior cervical decompression and fusion (ACDF), the most commonly performed procedure, poses risks of pseudoarthrosis, and adjacent segment disease (ASD).1,2 An emerging alternative treatment option is prosthetic total disc replacement (TDR),3 which preserves segmental mobility. Our group previously developed a biological TDR device using composite AF/NP disc-like construct with viable cells and mechanical properties analogous to the native discs in a rat tail model.4 In this study, we evaluated the in vivo efficacy of this tissue-engineered intervertebral disc (TE–IVD) in a beagle cervical model assessing radiological and histological parameters. Material and Methods TE-IVD construction: Canine-sized TE–IVDs were constructed as previously described.4 Cervical IVDs from skeletally mature beagles were separated into AF and NP tissues; component cells were isolated and cultured in vitro. Cultured NP cells were seeded with alginate, injected into a predesigned mold, and encircled with two layers of an AF cell laden collagen gel. The combined construct was kept in media for 2 weeks as the surrounding annulus fibrous aligned and contracted until required TE–IVD diameter was attained. Experimental Protocol: Overall, eight skeletally mature beagles were divided into the following two groups: the control group (n = 2) underwent discectomy with fully resected IVDs, and the experimental group (n = 6) underwent TE–IVD implantation postdiscectomy. Adjacent proximal segments served as internal healthy controls. Postoperative X-ray and MRI were taken at 2 and 4 weeks; disc height indices5 and NP hydration using a pre-established algorithm6 were analyzed. Beagles were humanely killed at 4 weeks for histological assessment. Results TE–IVDs were successfully implanted postdiscectomy (Fig. 1A, B). At 2 weeks, MRIs of TE–IVDs revealed T2 high intensity with acute outer inflammation because of the surgical invasion, which faded by 4 weeks. At 4 weeks, TE–IVDs maintained position in the disc space with relatively increased T2 intensity, whereas discectomized segments manifested as black discs (Fig. 1C, D). These findings suggest that the implanted TE–IVDs engraft in the disc space despite significant biomechanical demands of the beagle cervical environment. In fact, disc height indices of the TE–IVDs and discectomized discs were 71 and 49%, respectively, of that of healthy control discs. Likewise, MRIs revealed that NP hydration of the implanted TE–IVDs was over 70% of that of healthy discs. Histological assessments further demonstrated chondrocyte-like cell viability in the TE–IVD, abundant proteoglycan content in the extracellular matrices, and substantial integration into host tissues without signs of immune reactions.