Abstract
Introduction
The viscoelastic cervical disk prosthesis CP-ESP is an innovative one-piece deformable but cohesive interbody spacer. It is an evolution of the LP-ESP lumbar disk implanted since 2006. The implant provides 6 full degrees of freedom including shock absorption. The design allows a limitation for 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. It thus differs substantially from current prostheses.
This study reports the clinical results of a prospective observational study series of 89 patients who are representative of the current use of the ESP implant since 2012.
The radiological results are focused on the evolution of the mean center of rotation (MCR) as an additional information to the range of motion (ROM) for the evaluation of the quality of spine movement.
Materials and Methods
89 patients (33 males, mean age 45 years [28–60], 107 implants) were included for an open, prospective and non-randomized study between October 2012 and December 2015.
One level patients were at C3C4 (3), C4C5 (3), C5C6 (41) C6C7 (24) C7T1 (1)
Two levels patients were C4C5/C5C6 (3), C5C6/C6C7 (12), C6C7/C7D1 (1) and 3 levels C4C5/C5C6/C6C7 (1)
Results
Clinical data were obtained preoperatively and at 3, 6, 12 and 24 months (mean ± SD):
| Neck VAS: | 5,85±2,24 | 2,34±1,95 | 1,42±1,54 | 2,25±1,75 | 2,1±1,1 |
| Arm VAS: | 6,5±1,95 | 2,22±1,95 | 1,5±2,0 | 3±2,78 | 1±2,5 |
| NDI (%): | 55,8±15,2 | 29,5±17 | 18,9±15 | 31±13 | 21±11 |
| SF 36 PCS (%): | 31±22,5 | 50±14,9 | 65±8,4 | 44±12,8 | 54±12 |
| SF 36 MCS (%): | 32±13,9 | 51±10,9 | 69±8,5 | 54±6,7 | 59±8 |
We did not observe local ossifications.
One case of side level degeneration was observed after 12 months in a C5C6 mono-segmental disk replacement (retrospectively this patient was a good case for a double initial implantation). To date the patient has not been re-operated.
Two cases were revised (one C5C6 implant for bone ingrowth failure at 6 months and one C4C5 case for painful hypermobility in a globally stiff spine).
Range of motion was obtained after 6 months and maintained at 24 months.
Radiological study of the location of the mean center of rotation at the prosthesis level and adjacent disks demonstrated the adaptation ability of the implant.
Conclusion
The concept of the ESP prosthesis is different from that of the “first generation” articulated devices currently used in the cervical spine. This study reports encouraging clinical results about pain, function and kinematic behavior.
An interesting point is the evolution of the Mean Centers of Rotation in the
post-operative course. This adaptation ability is one of the main features as we need to consider the mean and long term evolution of the global cervical posture and mobility after a cervical disc replacement.
Additional studies and longer patient follow-up are needed to assess long-term reliability of this innovative implant.
