Towards personalized orthopaedic implants. Nico Verdonschot. BioMechTools

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1 Towards personalized orthopaedic implants Nico Verdonschot BioMechTools

2 Implants are larger relative to the area to be treated

3 Fatigue strength tests Considered an issue with 3-D printed orthopaedic implants

4 How high is the load on a hip? Measuring hip forces with hollow neck prosthesis

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7 How much force on a total knee replacement?

8 Force (xbw) Forces in the knee during walking Courtesy: Dr. D Lima Time (sec)

9 Knee forces while skiing Courtesy: Dr. D Lima

10 Evidence Based Medicine Large patent cohorts Why is the implant performing well in some patients and not in others while Percentage non-revised 100 patients get exactly the same treatment? Patients younger than 50 years Why is it that around 25% of total knee replacement patients are not satisfied? Years after implantation Swedish Registry

11 Everybody is similar, but different Clear trend: Adapting the implant to the patient instead of adapting the patient to the implant

12 Imaging Patient specific placement Patient specific implant shape Softer materials

13 Imaging Patient specific placement Patient specific implant shape Softer materials

14 Getting shapes from imaging MRI CT

15 Getting shapes from imaging MRI CT

16 CT versus MRI MRI Sometimes inaccurate bone mapping CT Faster, less expensive than MRI Easier bone segmentation

17 Radiation Exposure MRI: none CT: very limited -Only the lower body (less tissue, lower dosis) -Effect very limited (no children) -4.5 msv is about living 2 years in US -Much lower than restricted msv/year

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19 3-D printed representation of segmented bones CT MRI CT MRI Note: there are many ways to segment bones from scans

20 Imaging Patient specific placement Patient specific implant shape Softer materials

21 CT or MRI based patient specific instrumentation

22 CT or MRI based patient specific instrumentation Less inventory No intramedullary instruments Faster surgery

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24 Accurate placement also obtained with Computer Navigation

25 Patient specific instrumentation Computer Navigation

26 Patient specific instrumentation versus navigation

27 Imaging Patient specific placement Patient specific implant shape Softer materials

28 Big interst in added manufacturing for standard implants because of porosity possibilities Ti6Al4V CoCr Stainless steel

29 Big interst in added manufacturing for standard implants because of porosity possibilities

30 Ingrowth assessment of porous structures

31 Ingrowth assessment of porous structures 2 weeks 4 weeks 6 weeks Indicates highest speed of bone ingrowth in week 1 & 2

32 Personalized implants: very effective used in non-standard cases

33 Cups with variable porosity/stiffness leading to more physiological bone stresses AC BD AC BD Figure 1. Sections used for results analysis.

34 Simulating the musculoskeletal system of patients and calculating forces on implants and joints

35 Cups with variable porosity/stiffness leading to more physiological bone stresses Equivalent elastic strain Natural Solid Ti Variable porous Ti

36 Bone shapes and therefore kinematics are different in each patient

37 The knee-cap moves differently after placement of a prosthesis (25% of patients are not satisfied)

38 Patient specific knee implants

39 Patient specific

40 Imaging Patient specific placement Patient specific implant shape Softer materials

41 Will a polymer (PEEK) prosthesis create more physological stresses in the bone? Metal component Metal Polymer healthy Polymer component

42 The development of a personalized meniscus prosthesis

43 Conclusions: Loads on implants are substantial (fatigue failure testing is important) MRI and CT can be used to determine patient specific cutting blocks and implants Big interest to EBM or SLB applications to orthopaedic implants to optimize porosity (ingrowth and stiffness) and kinematics (shape) Printing softer materials perhaps interesting for future applications

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