MBP 3970Z – 6 Week Project By: Patrick Lai Supervisor: Matt Teeter, Ph.D.c Medical Biophysics

1. 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

2. 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]

3. Mechanics of TKA and THA

4. Metallic Debris • Due to the mechanics and constant motion of implant • Metal debris and others can be embedded in the polyethylene liners

6. 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

7. 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

8. Approach • Conduct segmentation of scans using micro CT images • Analyze data through ‘Paraview’ and ‘Microview’ software.

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

10. 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

11. 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.

13. 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

15. Histogram

16. Surface reconstruction of Hip Poly

18. Video

19. Volume Data – Knee implants

20. Results • Of the 11 specimens scanned: • 5 hip poly and 6 knee poly • 2 Hips polysand 2 Knee polys had anomalies

21. Discussion- Examination of Artifacts – K722

22. MIP – K722

23. Surface rendering

24. 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

25. Future studies • The effect of outer artifacts on the volume measured inside • Methods of reducing artifacts

26. 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

27. Acknowledgements • Matt Teeter Ph.D.c • LyndsaySommervillePh.D.c

28. Works Cited 1) Bohm, E., M. J. Dunbar, et al. (2009). "The Canadian Joint Replacement Registry—what have we learned?" ActaOrthopaedica81(1): 119-121. 2) Hayashi, A. (2009). "Modes of failure can predict outcomes after revision TKA " American Academt of Orthopaedic Surgeons News.

29. Question Period