A Dynamic Pre-Clinical Testing Protocol for Intervertebral Disc Replacement Devices

Abstract

Back pain is a common complaint and the origin of this frequently attributed to degenerativedisc disease. In the most severe cases, the integrity of the disc and surrounding tissue is lostto such an extent that surgical intervention is necessary.Fusion procedures are commonly used to treat severely degenerated discs. Yet this is knownto alter the biomechanics of the operated level, and may create a progression ofdegenerative decline. Total disc replacement has emerged as a viable treatment but thecomplexity of the spine is reflected in the clinical results, which trail far behind the successof hip and knee arthroplasty. This may be due to a failure of total disc replacementprocedures to restore the natural biomechanics of the spine.The present study has led to the development of a dynamic pre-clinical testing protocol toquantitatively assess the efficacy of disc replacement devices. A six-axis spine simulator wasdesigned and built, and the stiffness matrix testing of porcine lumbar specimens wascompleted, both with and without an axial preload. Intact specimens were tested, and thetesting repeated after a total disc replacement procedure with a DePuy In Motion artificialdisc. This is the first study to complete dynamic six-axis spinal testing of this kind.The testing demonstrated the disc replacement device compared favourably with the intactporcine disc both in shear and axial stiffness. However, the low-friction, double ball andsocket design of the In Motion device lacks stiffness in the three rotational axes, and it isunstable in lateral bending. Rotations are the primary movements in the spine, and it iscrucial if the natural biomechanics are to be restored, that a disc replacement device shouldreplicate the stiffnesses of these axes.The next generation of disc replacement devices feature elastomeric materials that maymore closely replicate the natural intervertebral disc. From patents registered with DePuy,this may also be true of the next generation of In Motion disc.This research provides a means to complete standardised performance tests of new spinaldevices and lays the foundations for future comparison studies. Additionally, the spinesimulator and testing protocol would provide valuable data during the design stage of newtotal disc replacements, aiding the development of the next generation of artificial discs.

Date of Award	29 Feb 2012
Original language	English
Awarding Institution	University of Bath
Supervisor	Sabina Gheduzzi (Supervisor) & Tony Miles (Supervisor)