mbp 3970z – 6 week project by: patrick lai supervisor: matt teeter, ph.d.c medical biophysics
DESCRIPTION
Quantification of Third-Body Debris in Retrieved Polyethylene Orthopedic Components Using Micro-Computed Tomography. MBP 3970Z – 6 Week Project By: Patrick Lai Supervisor: Matt Teeter, Ph.D.c Medical Biophysics. Introduction. - PowerPoint PPT PresentationTRANSCRIPT
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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
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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]
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Mechanics of TKA and THA
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Metallic Debris
Due to the mechanics and constant motion of implant
Metal debris and others can be embedded in the polyethylene liners
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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
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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
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Approach
Conduct segmentation of scans using micro CT images
Analyze data through ‘Paraview’ and ‘Microview’ software.
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Hypothesis
Using X-ray CT technology, third-party debris can be segmented from the polyethylene portions of a retrieved component
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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
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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.
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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
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Histogram
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Surface reconstruction of Hip Poly
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Video
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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
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Results
Of the 11 specimens scanned: 5 hip poly and 6 knee poly
2 Hips polys and 2 Knee polys had anomalies
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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
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MIP – K722
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Surface rendering
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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
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Future studies
The effect of outer artifacts on the volume measured inside
Methods of reducing artifacts
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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
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Acknowledgements
Matt Teeter Ph.D.c Lyndsay Sommerville Ph.D.c
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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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QuestionPeriod