RATIONALE FOR DESIGN CRITERIA FOR THE SECOND GENERATION OF INTERVERTEBRAL DISC PROSTHESIS

Abstract

First-generation intervertebral disc prostheses (IDPs) have well-established design fea-tures, but an inconsistent functional performance and they are not entirely accepted for clinical use. Currently, second-generation IDPs aim to overcome first-generation problems. Design features and performance of IDPs are related from first- to second-generation, but the relationship is unclear. In 1990, Hedman et al. determined design criteria for the first generation, but the lit-erature has not reported any further criteria for the second generation. This paper is focused on design criteria for second-generation prostheses, clarifying the relationship between the design features and performance of IDPs. We analyzed biomechanical prop-erties of natural intervertebral discs and technological evolution of IDPs to characterize functional performance. A group of functional parameters were identified. A comprehensive review of the literature regarding design criteria showed inconsistent and ambiguous criteria. So, a structure of criteria based on information content is proposed to avoid these conflicts. The criteria are structured into three parts including the functional parameters. In a straight relation to functionality, three design criteria are sufficient to evaluate holistically the features of the second-generation IDPs. The criteria avoid the absence or incongruence of information of the design features and relate the performance of IDP to its features in the route to overcome functional problems.