Introduction: Current total disc prostheses are 2- or 3-pieces devices, including 1 or 2 bearing surfaces, and providing 3 or 5 degrees of freedom but with no, or very little, resistance. The ESP^® is a one-piece deformable implant made of silicon and polycarbonate polyurethane elastomer securely fixed to titanium endplates. It allows limited rotation and translation with elastic return. This cushion without fixed rotation center achieves 6 degrees of freedom including shock absorption. An earlier attempt to use elastomers (Acroflex^®) failed clinically due to the polymer. This highlights the need for accurate in-vitro fatigue testing and clinical evaluations.

Methods: In-vitro fatigue testing with more than 40 millions cycles were performed on different samples for compression, flexion-extension bending, lateral bending, torsion and shear. A prospective trial was initiated in 2004 for L3L4, L4L5 and L5S1 levels. Total disc replacements have been performed in 153 lumbar levels through extra-peritoneal mini-invasive anterior approach

Results: After in-vitro testing, microscopic examination showed that the polymer core remained unchanged without evidence of cracking or other degradation. Gravimetric analysis revealed insignificant changes in weight. The geometrical characteristics and the cohesion of the implants remained stable. After 3 years clinical experience, there was no device related complication, except one early revision for a post-traumatic implant migration. VAS and ODI scores improvements were equivalent to other published series.

Discussion and Conclusion: In-vitro fatigue testing and short term results of the innovative ESP^® prosthesis demonstrate the reliability of the concept. The results are equivalent to other series with conventional implants.