The Spine Journal
Volume 10, Issue 7 , Pages 602-609, July 2010

Restoration of compressive loading properties of lumbar discs with a nucleus implant—a finite element analysis study

  • Daniel G.T. Strange, MEng

      Affiliations

    • Spine Service, Department of Orthopaedic Surgery, St George Hospital, University of New South Wales, Kogarah NSW 2217, Sydney, Australia
    • Department of Engineering, Cambridge University, Cambridge CB2 1PZ, UK
    • ,
  • Sandie T. Fisher, BEngg

      Affiliations

    • Spine Service, Department of Orthopaedic Surgery, St George Hospital, University of New South Wales, Kogarah NSW 2217, Sydney, Australia
    • ,
  • Philip C. Boughton, PhD

      Affiliations

    • Spine Service, Department of Orthopaedic Surgery, St George Hospital, University of New South Wales, Kogarah NSW 2217, Sydney, Australia
    • ,
  • Thomas J. Kishen, DNB (Ortho)

      Affiliations

    • Spine Service, Department of Orthopaedic Surgery, St George Hospital, University of New South Wales, Kogarah NSW 2217, Sydney, Australia
    • ,
  • Ashish D. Diwan, MBBS, PhD

      Affiliations

    • Spine Service, Department of Orthopaedic Surgery, St George Hospital, University of New South Wales, Kogarah NSW 2217, Sydney, Australia
    • Corresponding Author InformationCorresponding author. Spine Service, Department of Orthopaedic Surgery, St George Hospital, University of New South Wales, PO Box 541, Kogarah NSW 2217, Sydney, Australia. Tel.: (61) 2-9588-9622; fax: (61) 2-9588-9722.

published online 24 May 2010.

Abstract 

Background Context

Discectomy is a common procedure for treating sciatica. However, both the operation and preceding herniated disc alter the biomechanical properties of the spinal segment. The disc mechanics are also altered in patients with chronic contained herniation. The biomechanical properties of the disc can potentially be restored with an elastomeric nucleus replacement implanted via minimally invasive surgery.

Purpose

The purpose of this study was to determine whether the compressive characteristics of the intervertebral disc after a nucleotomy can be restored with an elastomeric nucleus replacement.

Study Design

A finite element model of the L4–L5 intervertebral disc was created to investigate the effect of the implantation of an elastomeric nucleus replacement on the biomechanical properties of the disc under axial loading.

Method

A L4–L5 physiologic intervertebral disc model was constructed and then modified to contain a range by volume of nucleotomies and nucleus replacements. The material properties of the nucleus replacement were based on experimental data for an elastomeric implant. The compressive stiffness, radial annular bulge, and stress distribution of the nucleotomy and nucleus replacement models were investigated under displacement-controlled loading.

Results

Removal of nucleus pulposus from the physiologic disc reduced the force necessary to compress the disc 2 mm by 50%, altered the von Mises stress distribution, and reduced the outward radial annular bulge. Replacing the natural nucleus pulposus of the physiologic disc with an artificial nucleus reduced the force required to compress the disc 2 mm by 10%, indicating a restoration of disc compressive stiffness. The von Mises stress distribution and annular bulge observed in the disc with an artificial nucleus were similar to that observed in the physiologic disc.

Conclusion

This study demonstrates that despite having different material properties, a nucleus replacement implant can restore the axial compressive mechanical properties of a disc after a discectomy. The implant carries compressive load and transfers the load into annular hoop stress.

Keywords: Finite element analysis, Intervertebral disc, Nucleus replacement, Nucleotomy, Compressive loading

To access this article, please choose from the options below

Login to an existing account or Register a new account.

  • Purchase this article for 31.50 USD (You must login/register to purchase this article)

    Online access for 24 hours. The PDF version can be downloaded as your permanent record.

  • Subscribe to this title

    Get unlimited online access to this article and all other articles in this title 24/7 for one year.

  • Claim access now

    For current subscribers with Society Membership or Account Number.

  • Visit SciVerse ScienceDirect to see if you have access via your institution.
 

 FDA device/drug status: not applicable.

 Author disclosures: DGTS (other relationships, Columna Pty Ltd); PCB (board of directors, Biometic Pty Ltd; research support: staff/materials, University of New South Wales; other relationships, Columna Pty Ltd); ADD (stock ownership, including options and warrants, Cellixe Pty Ltd; private investments, including venture capital, start-ups, Columna; consulting, Synthes Asia Pacific; trips/travel, Synthes; board of directors, Cellixe Pty Ltd; grants, Stryker Biotech; fellowship support, Stryker, Synthes).

 D.G.T. Strange and S.T. Fisher have performed sufficient work to be treated as equal first authors.

PII: S1529-9430(10)00311-6

doi:10.1016/j.spinee.2010.04.015

The Spine Journal
Volume 10, Issue 7 , Pages 602-609, July 2010

Article Tools

* Image Usage & Resolution