Spine Biomechanics

The area of spine biomechanics is extensively studied due to the prevalence of back pain and variety of therapeutic options to treat it. Exponent provides the highest quality technical and scientific support to assist our clients with understanding complex issues related to spine biomechanics. We specialize in providing rapid, focused, market-sensitive solutions to complex technical issues primarily focused on implantable devices used in the spine. Our engineers have extensive expertise in spine implant evaluation, spine implant retrieval analysis, finite-element modeling, and evaluation of spine biomechanics and spinal injuries, and we are widely published in these areas. We use these capabilities to help our clients solve a variety of challenges associated with device design, device performance, and device interaction with the environment.

Spine Implant Performance Evaluation

We perform mechanical and materials evaluation of spinal implants for clients with needs pertaining to patent evaluation/infringement issues, third-party design reviews, or in vitro testing for FDA regulatory submissions. Evaluations can also be conducted to assess spine implant performance, to answer specific questions related to materials (metal, polymers, and combinations), and functionality (dynamic stabilization, fusion, or motion preservation). We also have extensive experience in conducting biomechanical evaluations using cadaveric models and validated finite-element (FE) models of the spine. Our experience with in vivo animal models can also provide insight into mechanisms of metal ion release, tissue reaction (histology), and scanning microscopic evaluation (SEM) of spinal devices.

Spine-Related Testing Capabilities

Our laboratories have state-of-the art equipment and capabilities applicable to spine biomechanics testing such as:

  • Six-station MTS wear simulator with load-soak control station 
    • Designed for evaluated cervical and lumbar total disc replacements according to International Organization for Standardization (ISO) 18192 and American Society for Testing and Materials (ASTM) F2423
    • Capable of performing adverse wear testing profiles, including impingement and third-body modes of wear on total disc replacements
  • Testing load frames
    • Load range from 100N to 30kN; displacement range from micron resolution to as much as 1000 mm of travel
    • Temperature-controlled testing environments
    • Customized fixtures for mounting implants
    • Standard ISO and ASTM methods
    • Tissue testing applications: ligaments, muscle, disc, endplates
  • Cadaveric testing
    • Established relationships with donor foundations
    • Developed experimental protocols and obtained institutional review board (IRB) exemptions
    • Dissection and specimen preparation facilities on site
    • Access to surgeons for simulated implantation procedures
  • Imaging capabilities
    • High-resolution imaging for bone, soft tissues, and implants
    • Real-time radiographic imaging
    • Validated protocols for conducting computed tomography (CT), magnetic resonance imaging (MRI), and dual energy x-ray absorptiometry (DEXA)

Spine Implant Retrieval Analysis

We have established international retrieval programs to collect explanted spine implants, including fusion instrumentation, total disc replacements, and dynamic stabilization devices. As part of this program, we have developed custom-made implant retrieval kits and device-specific forms. Our international repository has provided us with the opportunity to examine retrieved spinal implants for wear patterns, failure mechanisms, corrosion, and deformation. We also have the expertise and capabilities to assist our clients with evaluation of fluid and tissue surrounding the implant, including histology, trace metal, and particle analysis.

Finite-Element Modeling 

Finite Element ModelOur group has extensive experience developing and using detailed, validated FE models of the thoracolumbar and cervical spine for evaluation of surgical procedures and biomechanics of specific spinal instrumentation. Specifically, we can incorporate the following:

  • Subject-specific model geometry based on medical images (x-ray, CT, MRI, intravascular ultrasound (IVUS), microCT, optical microscopy, cryosections)
  • Non-homogeneous bone moduli based on bone mineral density (via calibrated CT)
  • Nonlinear, tensile-only representations for major spinal ligaments
  • State-of-the-art intervertebral disc representation
  • Robust contact algorithms for facet interactions
  • Customized implant geometries

Additional Research Experience

In addition to the expertise described previously, our engineers and scientists have wide-ranging research knowledge and are extensively published in:

  • Burst fractures and osteoporotic vertebral compression fractures
  • Facet joint mechanics
  • Intervertebral disc mechanics (annulus fibrosus, nucleus pulposus, and endplate)
  • Spine finite-element analysis
  • Spinal manipulation
  • Tissue and trace-metal analysis
  • Wear and corrosion evaluation of retrieved implants
  • Medical imaging evaluations and characterization
  • In vivo characterization of low-back pain