SCYON 1

SCYON Orthopaedics AG

Wear Reduction in Artificial Joints (THR) by Geometric Means

SCYON Fossa Cup

SCYON 2

Kyon - SCYON

SCYON 3

Hip Bearing Solutions

•  Metal on Metal (The Evil) •  Ceramic on Ceramic (The Mean) •  Metal on Poly (The Forgiving)

SCYON 4

Metal on Metal Biologic reactions

SCYON 5

Metal on Metal Pseudotumors

•  “Pseudotumour” – a cystic or solid mass

•  Diagnose by MRI or ultrasound •  1% of MOM pts develop

pseudotumours by 5 years –  17pts, all female, –  Pandit et al (JBJS, 2008)

•  8% at 5yrs FU indicated by preliminary study from same group (AAOS 2009)

–  Prospective of 97 hips –  6 pseudotumours (5 female, 1 male)

SCYON 6

Ceramic - Ceramic

SCYON 7

Ceramic - Ceramic

•  Most studies report: –  20% noise, 10% squeaking –  1% persistent/ symptomatic squeaking

•  Varies from 0.7% to 40% •  2 studies report greater incidence

(8%-40%) with Ti-Mo-Zi-Fe alloy stem with V-40 taper neck profile

SCYON 8

Metal on UHMWPE (poly)

•  Gamma or ETO sterilized (non cross linked) has been associated to high frequency of mid-term radiographic osteolysis and subsequent clinical failure and revision.

•  1st Generation: two approaches (Melting and annealing) are used to reduce the concentration of residual free radicals after irradiation. Higher incidence of fatigue fractures

SCYON 9

What is the solution?

•  Metal/metal: Metallic debris and pseudo tumors •  Ceramic/ceramic: Squeaking •  Metal/highly x-linked poly: Fatigue failures

SCYON 10

Solution

•  Use material with longest proven clinical track record – standard gamma sterilized GUR 1020,

•  But address wear by geometry

• Bearing Contact

• Remove material where stress is high

Hertzian contact stress

SCYON 11

Solution

Standard geometry SCYON fossa

SCYON 12

Finite Element model

28 mm diameter CoCr head

UHMWPE layer

Ti shell support

Either standard liner geometry or SCYON fossa geometry

SCYON 13

Fossa Liner von Mises stresses reduced from 9.6 to 4.4 MPa

Standard geometry Point contact condition

Fossa geometry ring contact condition

SCYON 14

Stress distribution in Standard Geometry

SCYON 15

Stress distribution in Fossa Geometry

SCYON 16

Friction Factor

28 mm diameter CoCr head

UHMWPE layer

Either standard liner geometry or SCYON fossa geometry

N.E. Bishop, et. Al., Med. Eng. Physics., 30; 1057-1-64, 2008.

SCYON 17

Conventional poly liner geometry

Fluid film is quickly lost at the pole

SCYON 18

SCYON Fossa poly liner geometry

* N.E. Bishop, et. Al., Med. Eng. Physics., 30; 1057-1-64, 2008.

Sustained fluid flow out of the fossa maintains lubrication

Under pressure Flow restricted by seal

SCYON 19

SCYON Fossa Friction Factor

Zimmer * Friction factor 0.15

Conventional Geometry 0.12

SCYON Fossa 0.067

SCYON 20

Fossa Liner Wear testing

Endolab, Rosenheim, DE

Hip simulator according to ISO 14241-1

GUR 1020 UHMWPE liners

Vacuum packed in Nitrogen, gamma sterilized 25-37 kGy

28 mm diameter CoCr heads

liner with standard geometry as control

Compliant double shell and stiff shell backing

SCYON 21

Wear testing Wear distribution

Conventional Geometry Fossa Geometry

SCYON 22

In-vivo wear by RSA (RadioStereographic Analysis)

•  Precise determination of implant/bone migration and implant/implant displacement

•  RSA most precise method for determining in –vivo subsidence and wear rates

SCYON 23

RSA (RadioStereographic Analysis)

•  Spherical Tantalum markers are placed in the implants and bone

• Tantalum is biocompatible, well tolerated by the body, and very radio-opaque

• Markers are placed in the implants, the femur and pelvis

SCYON 24

Control points

X-ray tubes Focus 1 Focus 2

Film cassettes

Fiducial marks

SCYON 25

92

x

71

111 112

41 41

72

92

SCYON 26

Measurements of radiographs

112.344 123.334 112.45 132.45

2D coordinates

SCYON 27

RSA (RadioStereographic Analysis)

SCYON 28

SCYON head penetration in-vivo RSA

mm

months

+/- 2 std. error

SCYON 29

0.00

0.05

0.20

ETO !- Poly XLPE 10 SCYON

0.10 “safe level”

0.15

(Nivbrant , Digas)

mm

Annual in-vivo wear rates, RSA

SCYON 30

Conclusion

•  Fossa Liner reduces von Mises stress by factor 2

•  Fossa liner improves lubrication which reduces friction factor 2 times

•  Fossa Liner reduces poly wear by factor 3 in hip simulator (with CoCr heads and solid shells)

•  Initial 2 year results are very promising with annual wear rate of 25 microns.