#293 Effects of Mobile Core Technology on Fixation of Cervical Disc Replacement: Results from a FDA Investigational Device Exemption Trial of Mobi-C® Cervical Artificial Disc

General Session: Cervical Motion Preservation

Presented by: K. Kim

Author(s):

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

(1) University of California, Davis Medical School of Medicine, Neurological Surgery, Sacramento, CA, USA
(2) LDR Spine USA, Inc, Austin, TX, USA
(3) The Spine Institute, Santa Monica, CA, USA
(4) Centre Hospitalier Universitaire Dijon Le Bocage Central, Dijon, France
(5) Clinique St Martin – Centre Aquitain du Dos, Mérignac, France
(6) Centre Hospitalier Régional Orléans, Orléans, France
(7) Clinique de Millénaire, Montpellier, France
(8) Retired, Nice, France
(9) Clinique du Parc, St Priest en Jarez, France
(1) 0Clinique du dos AXIS, Hornu, Belgium
(1) (1) Texas Back Institute - Plano, Plano, TX, USA
(1) (2) Hôpitaux Universitaires de Strasbourg, Strasbourg, France
(1) (3) Centre Hospitalier Universitaire Bordeaux – Groupe Hospitalier Pellegrin, Bordeaux, France

Abstract

Introduction: Anterior cervical discectomy and fusion (ACDF) has long been the standard treatment for cervical degenerative disc disease. A goal of ACDF is immobilization of the affected segment but this could negatively affect the adjacent segments. As an alternative, total disc replacement (TDR) devices have been designed to allow motion at the treated segment. Maintaining the motion reduces the additional stress at the adjacent segments known to occur after ACDF. The Mobi-C cervical artificial disc (LDR Medical; Troyes, France) is unique because it contains a mobile core which allows for translational movement of the adjacent vertebral bodies in the transverse plane, as opposed to a fixed core design which affords motion only about a point in space. This design is thought to reduce the stress and shear strain at the bone/implant interface and to allow for natural motion of the treated and adjacent segments. Relieving stresses at the bone/implant interface allows for sufficient fixation of the prosthesis with minimally invasive anchoring and reduces the risk for device migration. Furthermore, maintenance of natural motion at the treated segment may protect against adjacent segment degeneration.

Methods: A prospective, randomized, multicenter, controlled FDA IDE study was conducted to analyze the safety and efficacy of TDR with Mobi-C to treat symptomatic cervical degenerative disc disease at a single level. 164 patients enrolled in the study were randomized to the TDR group. The primary outcome measures of this study are anterior-posterior (AP) translation and range of motion (ROM) at the treated (index) and adjacent levels and instances of device migration. Flexion/extension films were collected preoperatively and at 36 months post-operatively. All radiographic analysis was conducted by Medical Metrics Inc., Houston, Tx. (MMI). Significant migration is defined as a device that has moved greater than 3 mm anteriorly or posteriorly after implantation.

Results: At 36 months, the study had no instances of significant device migration. Translation at the index level increased significantly from 0.9 mm at baseline to 1.4 mm at 36 months. The translations at superior and inferior levels both increased, but were not significantly different from baseline to 36 months. The ROM at the index level increased from 8.3° to 10.0° at 36 months post-op. The ROM for the superior and inferior levels also increased, but not significantly. (Table 1)

Discussion: Follow-up radiograph data demonstrate that Mobi-C maintains or improves flexion/extension movement at the index and adjacent segments. The analysis of translational motion validates the mobile core design: the AP translation at both the treated and adjacent segments is either maintained or improved. Fixation to native bone was achieved as demonstrated by the lack of device migration. The lack of significant changes in motion at the adjacent levels also suggests that by allowing physiologic motion at the treated segment, motion at the adjacent segments is maintained in both the rotational and translational component.

Table 1