#298 Biomechanical Testing of the Mobi-C® Cervical Artificial Disc

Oral Posters: Cervical Arthroplasty

Presented by: H. Bae

Author(s):

H.W. Bae (1)
J. Beaurain (2)
P. Bernard (3)
D. Thierry (4)
J.-M. Fuentes (5)
A. Hovorka (6)
J. Huppert (7)
A. Jodaitis (8)
K. Kim (9)
R. Rashbaum (1)0, J.-P. Steib (1) (1)
J.-M. Vital (1) (2)

(1) Cedars-Sinai Spine Center, Department of Surgery, Div of Orthopaedics, Los Angeles, CA, USA
(2) Centre Hospitalier Universitaire Dijon Le Bocage Central, Dijon, France
(3) Clinique St Martin – Centre Aquitain du Dos, Merignac, France
(4) Centre Hospitalier Régional Orléans, Orleans, France
(5) Clinique de Millénaire, Montpellier, France
(6) Private, Nice, France
(7) Clinique du Parc, St Priest en Jarez, France
(8) Clinique du Dos AXIS, Hornu, Belgium
(9) University of California, Davis, Sacramento, CA, USA
(1) 0Texas Back Institute, Plano, TX, USA
(1) (1) Hopitaux Universitaires de Strasbourg, Strasbourg, France
(1) (2) Centre Hospitalier Universitaire Bordeaux – Groupe Hospitalier Pellegrin, Bordeaux, France

Abstract

Introduction: Total disc replacement (TDR) is an alternative to anterior cervical discectomy and fusion (ACDF) for treatment of cervical degenerative disc disease. There are many different design concepts of TDR devices, and a wide range of materials used across these various designs. The Mobi-C cervical artificial disc was designed to enable natural motion of both the treated and untreated segments of the cervical spine and to support physiologic loads and ranges of motion experienced in the spine. To validate the design, the materials of manufacture, and to establish the biomechanical profile of the Mobi-C device, an extensive in vitro test battery was conducted.

Methods: Devices were tested under axial compression (static and dynamic), compression shear (static and dynamic), creep and stress relaxation, static expulsion (full device and mobile insert only), subsidence, and subluxation. Long term simulated use wear testing was conducted, and wear particulate from the analysis was analyzed. All testing was conducted to appropriate ASTM/ISO standards for evaluation of device materials. The Mobi-C consists of CoCrMb alloy endplates and UHMWPE mobile core. Relevant literature was used to define acceptance criteria for each test.

Results: Selected test results are shown in Table 1. Static and dynamic axial compression failure loads exceeded normal physiological load. Combined static compression shear withstood over 4 times the acceptable criteria and dynamic compression shear ran to 10 million cycles with no failures. Creep and stress relaxation testing indicated no permanent deformation greater than 1mm. Expulsion testing of the full device and the UHMWPE core both confirm the Mobi-C can resist push-out forces greater than physiologic loads in the spine. Subsidence testing indicated a high resistance of the Mobi-C device from subsiding into the vertebral endplates. The Mobi-C also met the required criteria for subluxation of the inlay from the endplate, the shear load required to produce subluxation was greater than physiological conditions in the spine. Wear tested devices successfully passed 10 million cycles of coupled motion and wear particle analysis was consistent with published data on similar devices; no third body wear or wear abnormalities were observed. The wear testing particles were polymetric, consistent with wear of the polyethylene component.

Table 1: Results of biomechanical in vitro testing of the Mobi-C TDR device.

Discussion: The Mobi-C device was designed to allow for natural physiological motion of the spine while also sustaining the biomechanical loads that are experienced in the intervertebral space of the cervical spine, including long term use in vivo. The Mobi-C met or exceeded all established criteria when subjected to laboratory testing. The lack of metal wear particles produced during wear testing indicates the Mobi-C is suitable for long term implantation in the cervical spine without the metal wear concerns of metal on metal implants. While in vitro testing alone cannot determine the safety of an orthopedic implant, the results of mechanical tests of the Mobi-C device indicate that the device is able to withstand the mechanical loads necessary to function for long term duration in the cervical spine.

Table 1