Parameters that effect spine biomechanics following cervical disc replacement

Abstract

Total disc replacement (TDR) is expected to provide a more physiologic alternative to fusion. However, long-term clinical data proving the efficacy of the implants is lacking. Limited clinical data suggest somewhat of a disagreement between the in vitro biomechanical studies and in vivo assessments. This conceptual paper presents the potential biomechanical challenges affecting the TDR that should be addressed with a hope to improve the clinical outcomes and our understanding of the devices. Appropriate literature and our own research findings comparing the biomechanics of different disc designs are presented to highlight the need for additional investigations. The biomechanical effects of various surgical procedures are analyzed, reiterating the importance of parameters like preserving uncinate processes, disc placement and its orientation within the cervical spine. Moreover, the need for a 360°dynamic system for disc recipients who may experience whiplash injuries is explored. Probabilistic studies as performed already in the lumbar spine may explore high risk combinations of different parameters and explain the differences between ''standard'' biomechanical investigations and clinical studies. Development of a patient specific optimized finite element model that takes muscle forces into consideration may help resolve the discrepancies between biomechanics of TDR and the clinical studies.Factors affecting long-term performance such as bone remodeling, subsidence, and wear are elaborated. In vivo assessment of segmental spine motion has been, and continues to be, a challenge. In general, clinical studies while reporting the data have placed lesser emphasis on kinematics following intervertebral disc replacements. Evaluation of in vivo kinematics following TDR to analyze the quality and quantity of motion using stereoradiogrammetric technique may be needed.

The Envelope of Physiological Motion of the First Carpometacarpal Joint

“…In addition to advancing our basic understanding of CMC joint function, an accurate and complete understating of CMC kinematics provides a basis for evaluating CMC pathology, such as mechanically mediated aspects of OA [14], and it can inform the design of implants, where accurate replication of kinematics is essential for long-term success [15][16][17]. There is growing clinical evidence that implant failure is associated with the failure to replicate normal kinematics in the spine [31][32][33][34][35][36], wrist [37], knee [38,39], and shoulder [40][41][42][43][44][45]. In modeling, simplifying the thumb CMC joint as a ball-and-socket articulation rather than with the more complex harmonic profiles we identified, where the location of the screw axis can vary by >1 cm, could lead to substantial errors in the computation of ligament strains, cartilage stresses, and muscle moment arms.…”

Effect of screw position on load transfer in lumbar pedicle screws: a non-idealized finite element analysis

“…However, as suggested many years ago by Halvorson (Halvorson, Kelley, Thomas, Whitecloud and Cook 1994), and more recently by Dreischarf et al,(Dreischarf et al 2014) Goel et al (Goel et al 2012), Meijer et al (Meijer et al 2011), Chevalier et al (Chevalier and Zysset 2012), and Little et al (Little and Adam 2012), FEA based on a non-idealized series of models, or patient-specific models, could be of greater value.…”

Finite element analysis of a ball‐and‐socket artificial disc design to suppress excessive loading on facet joints: A comparative study with ProDisc

“…The stresses in the intervertebral discs at the adjacent levels were similar in the ProDisc and NewPro, as the spinal motions were preserved at surgical level. The stresses in the artificial discs were investigated to determine the location of maximum stress during spinal motion, as in previous studies . The maximum stresses were similar in the ProDisc and NewPro in flexion, extension, and torsion, whereas maximum stress was greater in the NewPro in bending.…”