CUSTOM IMPLANTS Research, Regenerative Medicine and Personalized Surgery at Rizzoli Orthopedic Institute CUSTOM ENDOPROTESI: Design of patient-specific ankle prosthesis for replacement surgery obtained through metal alloys 3D printing and polyethylene Design of customized endoprosthesis for ankle through geometric-biomechanical design and 3D printing technology to improve joint surfaces replacement by artificial endoprosthesis

1. CUSTOM ENDOPROTESI: Design of patient-specific
ankle prosthesis for replacement surgery obtained
through metal alloys 3D printing and polyethylene
Laboratorio Analisi del Movimento
Istituto Ortopedico Rizzoli

2. CUSTOM IMPLANTS 2
Total Ankle Replacement
Severe pain (*2M), end-stage osteoarthritis with motion limitation (*50K)
Ankle Fusion
(Arthrodesis)
Total Ankle Replacement
(TAR)
Ankle fusion and current TARs are inadequate to solve the problem
* Numbers refer to USA market only

3. CUSTOM IMPLANTS 3
Total Ankle Replacement
Cement fixation
Bone resection
Original CoR changed
Osteolysis
Impingement
Loosening (90-95%)
Subsidence
Infection
Instability
Edge loading
Salvage/revision
Malleolar fracture
Polyethylene wear and
dislocation
Subsidence
Instability
Impingement
Infection
Vascularity
Bone removal
Syndesmosis fusion
Non- delay-union
Groove at articulation
Long pegs, cortical window
Screw-based fixation
Stress-shielding
Still Flat-Ti & Nat-Ta?
Earlier complications
Sizing
Back to conforming 2-comp?!
Lateral access?!
Back to constrained?!
Back to cement?!
Cumbersome operative
technique!
Leardini et al. GIOT 2007; Giannini et al. Foot Ankle Surg 2000
Pioneers ‘70 Classics ‘80 Modern ‘90 Current 2000

4. CUSTOM IMPLANTS 4
TAR articular surfaces
Polyethylene
Metal

5. CUSTOM IMPLANTS 5
Image- and experimental- based study of the morphology of the articular surfaces,
in natural and prosthetic ankle joint
CT Imaging
Segmentation &
3D Renderings
3D Geometrical
Analysis Design & Manufacturing
of Artificial Surfaces
Testing: 3D Kinematics and Kinetics Analyses
CAOS & EFAS Best Paper Awards (2016)ankles (vitro/vivo)
TAR design
Anatomical approach

6. CUSTOM IMPLANTS 6
F
C L CM
B1
B2
A1
A2
Lateral
Sphere
Medial
Sphere
Tibia/Fibula Segment
Talus/Calcaneus Segment
Fixed
Sphere
CaFiL
TiCaL
C
Parenti-Castelli, Leardini et al., Med Bio Eng Comp 2007; J Biomech 2009
 Two ligament fibres
 Three rigid contacts:
A. 2 sph-pla at Ti-Ta, 1 sph-pla at Ta-Fi
B. 3 sph-sph
 3D mathematical description of passive kinematics
TAR design
Functional approach

7. CUSTOM IMPLANTS 7
TAR design
Functional approach

8. CUSTOM IMPLANTS 86 in-vitro implantation (‘99–’02), and about 1200 patients (Jul ‘03 – May ‘16)
TAR design
Anatomical-functional approach

9. CUSTOM IMPLANTS 9
Custom design
Imaging
Biomech. MODELS:
anatomical
Motion analysis
funct/anat
functional
Bones
Ligaments
Kinematics
D
E
S
I
G
N
D
E
S
I
G
N
d
i
m
e
n
s
i
o
n
Surgical/clinical
options:
• position
• shoulder/gutter
• fixation elements
• material
• cement / coating
• transverse plane
• chamfers
• insert
• cutting blocks?
D
E
S
I
G
N
f
i
n
a
l
…modelling
both ankles?!
Liverani et al. Materials and Design 2016

10. CUSTOM IMPLANTS 10
Imaging
 Selection of best option among devices currently available at IOR:
 CT based imaging:
- Standard CT (no soft tissue)
- Dual-Energy CT (enhancement of soft tissues)
- ConeBeam CT (3D and soft tissue, real joint loading)
 MRI based imaging:
- 1.5 T MRI
- 3.0 T MRI

11. CUSTOM IMPLANTS 11
Design of reference markers detectable by CT & MRI rigidly fixed on relevant
anatomical structures via plaster
HARD MARKER
with centered cavity Filled with a
CRYSTAL JELLY BALL hermetically closed
to avoid possible drying
Imaging

12. CUSTOM IMPLANTS 12
Regular CT Tissue 1Regular CT Tissue 1
Dual Energy CT Basal 1Dual Energy CT Basal 1
MRI 3T T2 FSMRI 1.5T cartilage new CBCT
Imaging

13. CUSTOM IMPLANTS 13
3D modelling and registration

14. CUSTOM IMPLANTS 14
SURFACE-TO-SURFACE ANALYSIS
Bone-cartilage registration via best fitting method
CBCT+3T
Standard
CT+1.5T
Standard CT+3T CBCT+1.5T
ConeBeam CT + 3T MRI
• LESS OVERLAPPING
• GREATER HOMOGENEITY
tibiatalus
3D modelling and registration

15. CUSTOM IMPLANTS 15
OBJECT MED D(mm) LAT D(mm) ANT D(mm) ANT CENTR D(mm) CENTR D(mm)
POST CENTR D
(mm)
POST
D(mm)
TALUS CT STANDARD 39.5 33.8 85.3 70.7 59.4 76.2 85.2(-)
TALUS CBCT 40.0 36.1 62.0 121.7 86.3 75.9 50.1(-)
TALUS DUALENERGY CT 42.5 36.9 45.3 92.1 62.3 74.2 80.8 (-)
TALUS CT STANDARD +COR 1.5T 45.5 36.0 146.8 76.6 91.9 60.3 68.8(-)
TALUS CT STANDARD +SAG 1.5T 41.3 35.1 87.0 95.9 120.5 69.7 114.6 (-)
TALUS CT STANDARD+ CUBE 3T 39.2 31.9 128.0 106.2 91.2 83.7 63.9
TALUS DUAL ENERGY CT +COR 1.5T 48.5 39.1 68.2 75.2 94.9 67.3 64.9
TALUS DUALENERGY CT +SAG 1.5T 51.5 41.3 77.4 95.8 127.0 65.5 51.6(-)
TALUS DUALENERGY CT + CUBE 3T 41.3 35.6 106.2 103.9 102.4 70.3 48.7
TALUS CBCT+COR 1.5T 57.9 41.6 89.4 81.6 90.8 99.0 61.9
TALUS CBCT+SAG 1.5T 53.6 45.0 136.0 95.0 139.4 73.6 (-) 39.1 (-)
TALUS CBCT+ CUBE 3T 48.7 39.3 118.9 100.5 99.7 85.9 86.8
DIFFERENCES IN ANATOMICAL PARAMETERS
BETWEEN IMAGING TECHNIQUES
3D modelling and registration
Siegler S et al, Clin Biomech, 29(1):1-6, 2014.

16. CUSTOM IMPLANTS 16
TAR design - virtual planning

17. CUSTOM IMPLANTS 17
TAR design - virtual planning

18. CUSTOM IMPLANTS 18
BOX size M Custom BOX design
+ 10%
Geometrical scaling of BOX TAR
(size: M)
TAR design - virtual planning

19. CUSTOM IMPLANTS 19
TAR implant-bone interface
Polyethylene
Metal

20. CUSTOM IMPLANTS 20Osseointegration
Chemistry & biocompatibility
Bone-implant interface material
Core material
- metals (e.g. CoCr, Ti alloys, Mg alloys)
- ceramics (Zr and Al based)
- metals (CoCr, Ti alloy, Tantalum)
- Calcium-phosphate based
(biomimetic coating, e.g. hydroxyapatite)
- biotolerant (distance osteogenesis)
- bioinert (contact osteogenesis)
- bioreactive (stimulating bone ingrowth)
“A direct structural and functional connection between ordered, living
bone and the surface of a load-carrying implant.”
Branemark (1985)
Stress-shielding
Topography
- surface roughness (10-50 micron)
- micron-scale and nano-scale (1 – 100nm)
Surface treatments
- sand-blasting
- plasma sprying
- electropolishing

21. CUSTOM IMPLANTS 21
Project workflow

22. CUSTOM IMPLANTS 22
Trabecular bone model
microCT – femoral bone
TopviewSideview
Density = 17%
Trabecular thickness = 150um
Trabecular Separation = 670um
Acknowledgement : Laboratorio di Tecnologia Medica (IOR)

23. CUSTOM IMPLANTS 23
Regular unit cells
CIRCULAR
CROSSING-ROD
Acknowledgement: CIRI-MAM (UniBO)

24. CUSTOM IMPLANTS 24
Regular unit cells porous scaffolds
TopviewSideview
SPHERICAL
Density-matched regular geometries
CIRCULAR CROSSING-ROD
Implant-to-bone control interface
Acknowledgement: CIRI-MAM (UniBO)

25. CUSTOM IMPLANTS 25
From STL to CrCo samples
Selective Laser Melting (CIRI-MAM, UniBO)
Acknowledgement: CIRI-MAM (UniBO)
9 x 9mm CoCr samples

26. CUSTOM IMPLANTS 26
Mechanical characterization
(ISO 13314, ASTM E9-09)

27. CUSTOM IMPLANTS 27
Geometrical validation
Circular lattice
hole diameter
Crossing-rod
strut dimension
Mean (SD) [µm] 761 ± 26 225 ± 27
STL nominal [µm] 800 200
Error [%] - 4.9 % + 12.7 %
Mean (±1SD) hole diameter measured across SLM circular samples and strut dimension of crossing-rod samples, and corresponding
STL files nominal dimensions.

28. CUSTOM IMPLANTS 28
SEM “round” sample
Geometrical validation

29. CUSTOM IMPLANTS 29
SEM “trabecular” sample
Geometrical validation

30. CUSTOM IMPLANTS 30
T0: 24 h T2: 2 weeks
Biocompatibilitycircularcrossing-rodtrabecularcontrol
top sidetop
Acknolwedgement: laboratorio BITTA (IOR)

31. CUSTOM IMPLANTS 31
Biocompatibility

32. CUSTOM IMPLANTS 32
SEM “round” sample + cells
Biocompatibility

33. CUSTOM IMPLANTS 33
SEM “trabecular” sample + cells
Biocompatibility

34. CUSTOM IMPLANTS 34
Conclusions
• Manufacturing: CoCr 3D porous structures are feasible via SLM
• Mechanical properties: similar to those of human bone 
(stress-shielding reduction)
• Biocompatibility: osteoblast-like cells proliferation and viability
is good on all geometries
• Results need to be confirmed in-vivo

35. CUSTOM IMPLANTS 35
3D printed porous implant-to-bone interface
Selective Laser Melting (CIRI-MAM, UniBO)

36. CUSTOM IMPLANTS 36
Grazie per l’attenzione
Ing. Alberto Leardini [leardini@ior.it]
Ing. Claudio Belvedere [claudio.belvedere@ior.it]
Ing. Paolo Caravaggi [paolo.caravaggi@ior.it]
Laboratorio Analisi del Movimento, Istituto Ortopedico Rizzoli