The Characterization of Particulate Debris Obtained from Failed Orthopedic Implants

A Research Report

Submitted in Partial Fulfillment of the Requirements for
Materials Engineering, 198B, Senior Research Project by:

Douglas J. Wood

San José State University
College of Materials Engineering
Spring 1993

ABSTRACT


This research investigated (using optical, scanning electron, and transmission electron microscopy) the metallic wear debris found at the site of the hip replacement implant when the implant was surgically replaced. The implants considered by this work consist of a Co-Cr-Mo alloy ball press fit onto a Ti-6Al-4V alloy 'stem' (i.e., a 'modular' system). Modular hip prostheses have been found to produce wear debris via various wear processes. This has been well documented in many publications concerning implant retrieval and analysis. The debris analyzed by this research has been confirmed to be titanium alloy (primarily b phase); not oxides or hydrides of titanium. Hydrogen plays an important role in the wear debris generation process. The range of sizes of debris analyzed by this research (and particle geometries) differ substantially from those previously reported. Two further important findings of this work are that surface defects such as hydrides and grit particles are present at the implant's surface and that the mesh pad that is diffusion bonded to the stem exhibits bonding defects. These and other observations can be implicated in a 'cascade' of debris generation within the patient that cause pain and other complications.

PREFACE


To the layperson, the field of materials science and engineering appears to be quite a narrow and specific discipline, but, as any student or practicing materials engineer will agree, it is nearly impossible to be an expert in every aspect of the field. Some choose to specialize in electronic materials, others may choose to concentrate on metallurgy or polymeric materials. Faced with a choice, I decided to concentrate in the area of biomaterials. I feel that my talents will be put to the best use when I can contribute directly to the improvement of someone's well being. Biomaterials engineers combine the principles of biology, medicine, and materials engineering to solve problems relating to materials that are to perform in the environment of the human body.

TABLE OF CONTENTS

  1. List of Figures
  2. List of Tables
  3. Introduction
  4. Background
  5. Overview of the Materials Science of Orthopedic Implant Systems
    • Available Implant Systems
  6. The Design Requirements for a Total Hip Replacement
  7. Mechanical Metallurgy and Passivation of Titanium Implant Alloys
    • The Passivation Layer
    • Commercially Pure Titanium 17Ti-6Al-4V/a+ b Alloys
    • Effect of Hydrogen on Microstructure
    • Hydrogen in Titanium: Sources of Hydrogen
    • Hydrogen in Titanium: Kinetics and Thermodynamics
    • Hydrogen in Titanium: Effects on Wear Resistance
    • The Service Environment of the Implant
    • Description of Fluid in Synovial Region
    • Description of Implant Loading Conditions
    • Modes of Failure
    • Corrosion Fatigue
    • Stem Loosening
    • Excessive Sliding Wear
    • Articulating Surface Wear
    • Ball-Stem Taper Joint Crevice Corrosion/Fretting Wear
    • Stem-Bone Micromotion Fretting Wear
    • Porous Coat-Stem Surface Fracture/Fretting/Corrosion
    • Bone Cement-Stem Surface Fretting Wear
  8. Scope of This Research
  9. Project Hypothesis
  10. Experimental Design
    • Rationale and Hypothesis
    • Materials and Procedures
  11. Results
    • Metallurgical Analysis of Unimplanted Stem
    • Optical Analysis
    • SEM Analysis of Unimplanted Stem
    • Microhardness
    • Particle Characterization
    • Control Particles
    • Retrieved Titanium Debris Particles
    • Scanning Electron Microscopy Results
    • Transmission Electron Microscopy
  12. Discussion of Results
    • Debris Generation and The Role of Hydrogen
  13. Conclusions
  14. Recommendations for Future Research
  15. References
  16. Acknowledgements


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