The innovative viscoelastic CP ESP cervical disk prosthesis with six degrees of freedom: biomechanical concepts, development program and preliminary clinical experience

Abstract

The viscoelastic cervical disk prosthesis ESP is an innovative one-piece deformable but cohesive interbody spacer. It is an evolution of the LP ESP lumbar disk implanted since 2006. CP ESP provides six full degrees of freedom about the three axes including shock absorbtion. The prosthesis geometry allows limited rotation and translation with resistance to motion (elastic return property) aimed at avoiding overload of the posterior facets. The rotation center can vary freely during motion. The concept of the ESP prosthesis is fundamentally different from that of the devices currently used in the cervical spine. The originality of the concept of the ESP® prosthesis led to innovative and intense testing to validate the adhesion of the viscoelastic component of the disk on the titanium endplates and to assess the mechanical properties of the PCU cushion. The preliminary clinical and radiological results with 2-year follow-up are encouraging for pain, function and kinematic behavior (range of motion and evolution of the mean centers of rotation). In this series, we did not observe device-related specific complications, misalignment, instability or ossifications. Additional studies and longer patient follow-up are needed to assess long-term reliability of this innovative implant.

Keywords: Artificial disk; CP ESP; Cervical disk prosthesis; Cervical spine mobility; Degenerative cervical disk; Rotation center; Viscoelastic disk replacement.

Fig. 1

Radiological images with CP ESP disk implant

Fig. 2

Description of the implant

Fig. 3

Description of the cycle testing according to ISO 18192 Norm

Fig. 4

Different configurations have been tested regarding the location of the rotation centers to address the worst case scenarios during the tests

Fig. 5

Mean centers of rotation (MCR) at the instrumented and at the upper and lower adjacent levels measured for flexion/extension using Spineview^® software; we can observe the adaptation of the implant including a translation for flexion

Fig. 6

a–f Mean centers of rotation (MCR) and mobility at the instrumented and at the upper and lower adjacent levels in a patient with global cervical kyphosis: adaptation during the follow-up from 3 to 24 months