Comparison of cervical spine biomechanics after fixed- and mobile-core artificial disc replacement: a finite element analysis.
METHODS
A biomechanical comparison between the intact C2-C7 segments and the C5-C6 segments implanted with two different constrained types (fixed and mobile core) of artificial disc replacement (ADR) using a three-dimensional nonlinear finite element (FE) model.


OBJECTIVE
To analyze the biomechanical changes in subaxial cervical spine after ADR and the differences between fixed- and mobile-core prostheses.


BACKGROUND
Few studies have investigated the changes in kinematics after cervical ADR, particularly in relation to the influence of constrain types.


METHODS
A FE model of intact C2-C7 segments was developed and validated. Fixed-core (Prodisc-C, Synthes) and mobile-core (Mobi-C, LDR Spine) artificial disc prostheses were integrated at the C5-C6 segment into the validated FE model. All models were subjected to a follower load of 50 N and a moment of 1 Nm in flexion-extension, lateral bending, and axial torsion. The range of segmental motion (ROM), facet joint force, tension on major ligaments, and stress on the polyethylene (PE) cores were analyzed. RESULTS.: The ROM in the intact segments after ADR was not significantly different from those of the normal cervical spine model. The ROM in the implanted segment (C5-C6) increased during flexion (19% for fixed and 33% for mobile core), extension (48% for fixed and 56% for mobile core), lateral bending (28% for fixed and 35% for mobile core) and axial torsion (45% for fixed and 105% for mobile core). The facet joint force increased by 210% in both fixed and mobile core models during extension and the tension increased (range, 66%-166%) in all ligaments during flexion. The peak stress on a PE core was greater than the yield stress (51 MPa for fixed and 36 MPa for mobile core).


CONCLUSIONS
The results of our study presented an increase in ROM, facet joint force, and ligament tension at the ADR segments. The mobile-core model showed a higher increase in segmental motion, facet force, and ligament tension, but lower stress on the PE core than the fixed-core model.
Department of Orthopaedic Surgery, Spine Center, Kyung Hee University Hospital at Gangdong, School of Medicine, Suwon, Korea.
Sang-Hun
SH
Lee
Yang-Jin
YJ
Im
Ki-Tack
KT
Kim
Yoon-Hyuk
YH
Kim
Won-Man
WM
Park
Kyungsoo
K
Kim
D019643:Arthroplasty, Replacement / Q000379:methods*; D001696:Biomechanical Phenomena; D002574:Cervical Vertebrae / Q000473:pathology / Q000503:physiopathology* / Q000601:surgery; D003198:Computer Simulation; D020342:Finite Element Analysis; D006801:Humans; D007403:Intervertebral Disc / Q000473:pathology / Q000503:physiopathology* / Q000601:surgery; D007405:Intervertebral Disc Displacement / Q000503:physiopathology* / Q000601:surgery; D008297:Male; D008953:Models, Anatomic; D016059:Range of Motion, Articular / Q000502:physiology; D016474:Weight-Bearing; D055815:Young Adult; D021801:Zygapophyseal Joint / Q000473:pathology / Q000503:physiopathology / Q000601:surgery