1. Orthopaedic Research Lab, West Palm Beach, Florida Biomechanical Mechanisms for Damage: Retrieval Analysis and Computational Wear Predictions in Total Knee Replacements Melinda K. Harman, MSc Director of Research Orthopaedic Research Laboratory West Palm Beach, FL

2. Orthopaedic Research Lab, West Palm Beach, Florida Acknowledgements: W. Andrew Hodge, MD Scott A. Banks, PhD Students:Michael Gleiber Karl Hein Egest Pone George Markovich, MD Martine LaBerge, PhD Lisa Benson, PhD John DesJardins, MSc Scott A. Banks, PhD Benjamin J. Fregly, PhD W. Gregory Sawyer, PhD

3. Orthopaedic Research Lab, West Palm Beach, Florida Implant Retrieval Program » Established 1992 » Donate prostheses after revision surgery or death Uniform Anatomical Gift Act (1987)Uniform Anatomical Gift Act (1987) Retrievals within the USA, Japan, EuropeRetrievals within the USA, Japan, Europe » Goals: Identify factors in successful prosthesis function and longevityIdentify factors in successful prosthesis function and longevity Evaluate body response to prosthesis Evaluate body response to prosthesis

4. Orthopaedic Research Lab, West Palm Beach, Florida »Anatomic studies - Tibial cartilage wear »In-vivo TKR fluoroscopy and PE wear »Computational models of TKR wear Topics »Motivation and Purpose

5. Orthopaedic Research Lab, West Palm Beach, FloridaMotivation »Wear remains a major concern in the design of Total Knee Replacements »Wear testing of new designs is expensive and may not replicate in vivo function »Computational tools for ‘casual’ design review and exploration are unavailable

6. Orthopaedic Research Lab, West Palm Beach, Florida To use information gained from retrieval analysis and in vivo fluoroscopy to develop computational models that can predict mild polyethylene wear in TKAPurpose

7. Orthopaedic Research Lab, West Palm Beach, Florida »Anatomic Studies - Tibial cartilage wear ACL deficiency alters tibiofemoral loadingACL deficiency alters tibiofemoral loading Cartilage wear may provide insight into knee kinematicsCartilage wear may provide insight into knee kinematics Harman, Markovich, Banks, Hodge: Wear patterns on tibial plateau from varus and valgus osteoarthritic knees. Clin Ortho Rel Res, 352:149-58, 1998Harman, Markovich, Banks, Hodge: Wear patterns on tibial plateau from varus and valgus osteoarthritic knees. Clin Ortho Rel Res, 352:149-58, 1998 »In-vivo TKR fluoroscopy and PE wear »Computational models of TKR wear Topics »Purpose

8. Orthopaedic Research Lab, West Palm Beach, Florida Methods: Cartilage damage »143 resected tibias with OA 74 male, 69 female74 male, 69 female age = 73+8 (48-94) yearsage = 73+8 (48-94) years »106 varus (18 3  +4  ) »37 valgus ( 167  +5  ) ACLVarusValgus Intact40% 49% Partial Disruption35% 27% Deficient25% 24% 100% 0% 63% * »Measure wear area and centroid location »error +1 mm

9. Orthopaedic Research Lab, West Palm Beach, Florida ACL Intact Knee Arthritis and Wear Anterior/middle of medial tibial surfaceAnterior/middle of medial tibial surface Less common for lateral compartment involvementLess common for lateral compartment involvement Lateral Medial

10. Orthopaedic Research Lab, West Palm Beach, Florida Kinematics Posterior femoral roll- back with knee flexionPosterior femoral roll- back with knee flexion Femoral external rotation with flexionFemoral external rotation with flexion ACL Intact Knee lateral condyle in red Lateral Medial Flexion

11. Orthopaedic Research Lab, West Palm Beach, Florida VALGUS Lateral Medial Lateral Medial VARUS Arthritis and Wear Posterior on medial tibial surface (varus)Posterior on medial tibial surface (varus) Posterior lateral compartment involvementPosterior lateral compartment involvement ACL Deficient Knee

12. Orthopaedic Research Lab, West Palm Beach, Florida Kinematics Anterior sliding of medial condyle with knee flexionAnterior sliding of medial condyle with knee flexion Femoral external rotation with flexionFemoral external rotation with flexion ACL Deficient Knee lateral condyle in red VARUS Flexion

13. Orthopaedic Research Lab, West Palm Beach, Florida »Tibial cartilage wear »In-vivo TKR fluoroscopy and PE wear Does in-vivo contact location correspond to wear location?Does in-vivo contact location correspond to wear location? Harman, Banks, Hodge: Polyethylene damage and knee kinematics after total knee arthroplasty. Clin Ortho Rel Res, 392:383-93, 2001.Harman, Banks, Hodge: Polyethylene damage and knee kinematics after total knee arthroplasty. Clin Ortho Rel Res, 392:383-93, 2001. Banks, Harman, Hodge: Mechanism of anterior impingement damage in total knee arthroplasty. J Bone Joint Surg, 84A:37-42, 2002.Banks, Harman, Hodge: Mechanism of anterior impingement damage in total knee arthroplasty. J Bone Joint Surg, 84A:37-42, 2002. »Computational models of TKR wear Topics »Purpose

14. Orthopaedic Research Lab, West Palm Beach, Florida »8 knees (6 subjects) with the same cemented PCL- retaining TKR »4 males / 2 females »age = 70 yr (65 to 76) »weight = 77 kg (57 to 93) »height = 170 cm (152 to 183) »Knee Society scores @ 1 year = 89 / 80 »frontal alignment = 6° valgus (2° to 10 °) Methods: Kinematics and Wear

15. Orthopaedic Research Lab, West Palm Beach, Florida »Joint Kinematics ±1.5º-2º ±0.5-1.0mm Fluoroscopy Methods »Edge Detect »Correct Image Distortion »Shape Match »Display/Verify IEEE Trans Biomed Eng 43(6):638-49, 1996. »Contact locations relative to tibial axis

16. Orthopaedic Research Lab, West Palm Beach, Florida In Situ Time (mo)Retrieval Reason Time (mo)Retrieval Reason 28autopsy 20autopsy 19patella resurf. 3infection 51autopsy 31osteolysis 36patella resurf. Time to Knee Fluoro (mo) 1L15 1R8 2L18 2R18 3L2 4R21 5R28 6L36 All subjects in-vivo fluoroscopy + implant retrieval

17. Orthopaedic Research Lab, West Palm Beach, Florida Articular Damage: Size and Location »Medial & lateral damage visually assessed 10x to 30x magnification10x to 30x magnification identified 8 damage modesidentified 8 damage modes »calibrated digital images »digitized circumference »damage area = % damage on medial or lateral plateau »damage location = A/P location relative to transtibial axis Scratch Burnish Pits Creep Striations Delamination Emb. Debris Abrasion mediallateral

18. Orthopaedic Research Lab, West Palm Beach, Florida RESULTS: Significant correlation between contact and damage location »Fluoroscopy predicts wear location 23% of medial variability23% of medial variability 56% of lateral variability56% of lateral variability »In vivo femoral contact location is significant predictor of polyethylene wear Spearman Correlation, (p<0.05)

19. Orthopaedic Research Lab, West Palm Beach, Florida Topics »Tibial cartilage wear »Fluoroscopy and PE wear »Computational models of TKR wear Can models predict in-vivo PE damage?Can models predict in-vivo PE damage? Fregly, Bei, Sylvester: Evaluation of an elastic foundation model to predict contact pressures in knee replacements. J Biomech, 36(11):1659-68, 2003.Fregly, Bei, Sylvester: Evaluation of an elastic foundation model to predict contact pressures in knee replacements. J Biomech, 36(11):1659-68, 2003. Fregly, Sawyer, Harman, Banks: Computational wear prediction of a TKR from in vivo kinematics. J Biomech, 38:305-14, 2005.Fregly, Sawyer, Harman, Banks: Computational wear prediction of a TKR from in vivo kinematics. J Biomech, 38:305-14, 2005. »Purpose

20. Orthopaedic Research Lab, West Palm Beach, Florida In Vivo Kinematic Data Gait One subject (65 year old female) One subject (65 year old female) KSS 90/100 @ 24 mo. KSS 90/100 @ 24 mo. Osteonics 7000 CR implant Osteonics 7000 CR implant Treadmill gait and stair activities Treadmill gait and stair activities Stair

21. Orthopaedic Research Lab, West Palm Beach, Florida Methods: Multi-body dynamic contact model 1.CAD models of same prosthesis used in fluoroscopy 2.Loads from different TKR patient during same activities 3.3 prescribed DOF from fluoro 1.AP translation 2.IR rotation 3.flexion 4.3 integrated DOF 5.gait and stair activities

22. Orthopaedic Research Lab, West Palm Beach, Florida 1.Contact pressures from elastic foundation theory 2.“bed of springs” over 3-D surfaces to push them apart 3.Computed contact forces, kinematics, contact pressures and slip velocities 4.two loading conditions 1.70-30 M/L load split 2.50-50 M/L load split Methods: Dynamic contact model

23. Orthopaedic Research Lab, West Palm Beach, Florida Damage for each tibial insert surface element was quantified as follows: 2. Wear Depth ( Archard and Hirst, 1956 ) Methods: Computational wear model 1. Damage Depth ( Schmalzried et al., 1998 ) (51 months) 3. Creep Depth ( Lee and Pienkowski, 1998 )

24. Orthopaedic Research Lab, West Palm Beach, Florida 1.Damage depth for combined gait and stair activities calculated using linear rule of mixtures: 2.Predicted total damage compared retrieved PE insert from same patient 3.Damage depth = deviation between original and worn surfaces where Methods: Computational wear model

25. Damage Predictions 85% Gait + 15% Stair 85% Gait + 15% Stair SimulationGait 70-30 load split Stair Post Mortem Retrieval 51 Months

26. Orthopaedic Research Lab, West Palm Beach, Florida Results: Damage Predictions SimulationRetrieval mediallateral

27. Orthopaedic Research Lab, West Palm Beach, Florida 16 Experimental Cases 4 flexion angles 4 flexion angles (0, 30, 60, 90 deg) 4 axial loads 4 axial loads (750, 1500, 2250, 3000 N) Contact Stress Models Assumptions Contact Stress Experiments Fregly et al., Journal of Biomechanics, 2003. 1.Linear material model

28. Orthopaedic Research Lab, West Palm Beach, Florida AssumptionsPeak Average Fregly et al., Journal of Biomechanics, 2003. 1.Linear material model

29. Orthopaedic Research Lab, West Palm Beach, Florida Despite many simplifying assumptions, results appear to replicate the ‘real thing’Despite many simplifying assumptions, results appear to replicate the ‘real thing’ 1.Linear material model - Fregly et al. J Biomech, 2003 2.Loads from different (but similar) individual 3.No creep relaxation 4.Wear uncoupled with geometry 5.Limited input activities 6.Parameters directly from literature Conclusions

30. Orthopaedic Research Lab, West Palm Beach, Florida Conclusions 1.Proof of Concept: Tibial insert damage predicted reasonably well by combining in vivo kinematics with computational modeling 2.Predicted maximum damage depths within 0.1 mm of the retrieved insert 3.Predicted damage areas in good quantitative and qualitative agreement with retrieved insert

31. Orthopaedic Research Lab, West Palm Beach, Florida »Tibial cartilage wear Joint laxity (ACL) is correlated with cartilage wear location Summary »In-vivo TKR Fluoroscopy and PE wear In vivo tibiofemoral contact location is correlated with damage location on retrieved PE inserts »Computational models of TKR wear Using in vivo kinematics, computational wear models accurately predict the damage location on retrieved PE inserts

32. Orthopaedic Research Lab, West Palm Beach, Florida Thank You!