In vivo biostability of polymeric spine implants: retrieval analyses from a United States investigational device exemption study

Abstract

The Dynesys System for stabilizing the lumbar spine was first surgically implanted in Europe in 1994. In 2003, a prospective, randomized, investigational device exemption clinical trial of the system for non-fusion dynamic stabilization began. Polycarbonate urethane (PCU) and polyethylene terephthalate (PET) components explanted from four patients who had participated in the study were analyzed for biostability. Components had been implanted 9-19 months. The explanted components were visually inspected and digitally photographed. Scanning electron microscopy was used to analyze the surface of the spacers. The chemical and molecular properties of the retrieved spacers and cords were quantitatively compared with lot-matched, shelf-aged, components that had not been implanted using attenuated total reflection Fourier transform infrared (FTIR) and gel permeation chromatography (GPC). FTIR analyses suggested that the explanted spacers exhibited slight surface chemical changes but were chemically unchanged below the surface and in the center. New peaks that could be attributed to biodegradation of PCU were not observed. The spectral analyses for the cords revealed that the PET cords were chemically unchanged at both the surface and the interior. Peaks associated with the PET biodegradation were not detected. GPC results did not identify changes to the distributions of molecular weights that might be attributed to biodegradation of either PCU spacers or PET cords. The explanted condition of the retrieved components demonstrated the biostability of both PCU spacers and PET cords that had been in vivo for up to 19 months.

Poly(carbonate‐urea‐urethane) networks exhibiting high‐strain shape‐memory effect

“…We expected that various morphologies of OCDs would result in different mechanical and thermal properties as well as the shape‐memory behavior of PCUUs. Furthermore, OCDs have been reported to improve the biostability of polyurethanes (PURs) when compared to those based on polyesters and polyethers, which is essential for purposes of long‐term medical applications, we would like to achieve by our PCUU system …”

In-vivo degradation of poly(carbonate-urethane) based spine implants

“…The PCU spacer is based on a soft polycarbonate segment and on an aromatic polyurethane hard segment (Bionate® 55D, DSM-PTG [36]). Previous literature studies reported an average Mw around 150,000–200,000 g/mol for this material [34]. The Dynesys® spacer has a thickness of 3.6 mm and an external diameter of 12 mm.…”

“…The length of the cord depends on the number of consecutive spacer and the diameter is 4 mm. The average Mw of the PET fibers in a similar system was reported to be around 75,000 g/mol [34]. …”

“…In one study [34], changes in the distribution of molecular mass and in the chemistry composition of the block copolymer were not observed, then absence of biodegradation was assumed. In another study name[35], the explanted devices showed permanent deformation, wear and surface damage.…”

Market approval processes for new types of spinal devices: challenges and recommendations for improvement

“…Over 40,000 patients have been implanted with this device since then [41], but with little published research. Thus, physicians did not report their clinical outcomes, even though the Dynesys Ò was new and its safety and efficacy had not yet been demonstrated.…”