Quantification of Third-Body Debris in Retrieved Polyethylene Orthopedic

Components Using Micro-Computed Tomography

MBP 3970Z – 6 Week ProjectBy: Patrick Lai

Supervisor: Matt Teeter, Ph.D.c Medical Biophysics

Introduction

Total knee arthroplasty (TKA) and total hip arthroplasty (THA) are common methods of treatment for joint failure.

Approximately 60 000 hospitalizations in Canada due to TKA s and THAs

Increase of 101% from 10 years ago [1] Average lifetime of implant: 10-15 years Main reasons for failure of implant:

› Osteolysis, Polyethylene wear, infection [2]

Mechanics of TKA and THA

Metallic Debris

Due to the mechanics and constant motion of implant

Metal debris and others can be embedded in the polyethylene liners

Complication of Debris

Wears away bearing surface› Increases frictional forces

Osteolysis› Resorption of bone die to debris in joint

capsule› Loosening of implant

Eventual failure

Objectives

To quantify the amount of metal debris embedded in a polyethylene liner using micro CT› Develop a novel way of segmentation› Find possible errors and fixes for CT

quantification

Approach

Conduct segmentation of scans using micro CT images

Analyze data through ‘Paraview’ and ‘Microview’ software.

Hypothesis

Using X-ray CT technology, third-party debris can be segmented from the polyethylene portions of a retrieved component

Methods

Polyethylene components were surgically retrieved from failed TKR and THR

Specimens were pre-screened to have known third party debris

Scanned using Micro CT

Surface rendering

Used Histogram to qualitatively set threshold levels

Microview takes threshold levels and creates isosurface

Using calibrated data from the scanner, the amount of voxels is converted into a volume

By making 2 surfaces: Polyethylene and Metal, the volume of the two are calculated.

Results

No other benchmark to compare to Therefore cannot quantitatively compare

volume sizes Visually inspect to qualitatively validate

volume data Volume data with visible artifacts are

also rejected

Histogram

Surface reconstruction of Hip Poly

Video

Volume Data – Knee implants

Specimen IRAL Number

Volume at Threshold 250 (mm^3)

Volume at Threshold 10000 (mm^3) Comments

K225 13288.446 0.196

K293 13652.791 1.655

K394 15866.734 0

Showed no metal, but non-zero metal

in MIP

K682 10731.801 0.537

K720 21051.426 0.405

K722 20734.746 101.496Outer artifact

Results

Of the 11 specimens scanned: 5 hip poly and 6 knee poly

2 Hips polys and 2 Knee polys had anomalies

Discussion- Examination of Artifacts – K722

Specimen IRAL Number

Volume at Threshold 250 (mm^3)

Volume at Threshold 10000 (mm^3) Comments

K225 13288.446 0.196

K293 13652.791 1.655

K394 15866.734 0

Showed no metal, but non-zero metal in MIP

K682 10731.801 0.537

K720 21051.426 0.405

K722 20734.746 101.496Outer artifact

MIP – K722

Surface rendering

Discussion

X-ray CT can be a valid method of analyzing amount of metal debris in a retrieved poly

7 of 11 polys measured without artifacts

The other 4 with artifacts are easily removed manually

Future studies

The effect of outer artifacts on the volume measured inside

Methods of reducing artifacts

Conclusion

Metal Debris can be quantified using micro CT method

Caution must be used to pre-screen images for artifacts before accepting results

Novel non-invasive way of determining volume

Acknowledgements

Matt Teeter Ph.D.c Lyndsay Sommerville Ph.D.c

Works Cited

1) Bohm, E., M. J. Dunbar, et al. (2009). "The Canadian Joint Replacement Registry—what have we learned?" Acta Orthopaedica 81(1): 119-121.2) Hayashi, A. (2009). "Modes of failure can predict outcomes after revision TKA " American Academt of Orthopaedic Surgeons News.

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