1. Patient Specific Implants - PSI Uni Knee for Perfection
Phil Davidson, M.D.
Davidson Orthopedics
Park City, UT
Dec 6 , 2018

2. No conflicts to report

3. PSI Uni Knee Resurfacing Advantages
Better Bone Fit
Bone Preservation
Convertability – Bridge in “younger” pts
Improved Biomechanics
Protect other compartments
Simplicity
Better Outcomes
Poor Alternatives for Lateral Uni
Lower Cost

4. PSI Uni Knee Implants & Jigs
Implants and Jigs 3D printed
More accurate fit may increase longevity
Improved Load bearing
Accommodate morphologic variability, “odd sizes and shapes”

5. PSI Uni Knee Implants and Jigs Fit Better
Patient-specific implants vs off-the-shelf implants
Greater cortical rim surface area coverage
77% v. 43% medially
60% v. 37% laterally

6. Tibial Uni Component Sizing Does size matter? Implication of mismatch
Chau R, Gulati A, Pandit H, Beard DJ, Price AJ, Dodd CAF, Gill HS, Murray DW: Tibial component overhang following unicompartmental knee replacement - does it matter? Knee 2009, Vol. 16, pp
Overhang of tibial tray by >3mm occurred in 9% of Oxford UKR in series n=160
5 yrs post op, this group had significantly worse Oxford Knee Scores (p=.0001) than those without overhang
Don’t want to undersize tray either, risk subsidence

7. PSI Knee - Bone Preservation
No subchondral bone resected from distal femur
Relatively small proximal tibial resection vs. Mobile bearing
Easier conversion to TKA for young pts

8. PSI Knee Biomechanics
Precise match of femoral “J” anatomy replicates roll back
More natural feel
Enhanced stability through ROM
Preservation of “other” knee regions

9. Finite element analysis PSI vs Off Shelf UKA
Bone coverage better, bone resection less for PSI
Medial PSI improved mechanics in Lateral compartment

10. PSI Uni Knee Implants and Jigs - SIMPLER
Much simpler instrumentation, fewer trays
Digitize limb, including size and alignment PRE-OP
MRI or CT
Avoid intraop “fiddling”
Avoid necessity for robot
Why not preserve subchondral bone????

11. Excellent Fit and Outcomes
31 patients with medial OA
Mean age 60 years. Minimum follow-up 17 months.
One aseptic loosening needed exchange; one acute late-onset infection
No further revisions/reoperations or complications.
X-rays showed an ideal fit of the implant with less than 2 mm subsidence or overhang in all cases.
VAS changed from 6.51 preoperatively to 1.11 postoperatively.
KSS improved from preop to postop
Functional KSS improved from mean to

12. Excellent Fit and Alignment Accuracy of Implant Match:
Mean: 0mm AP, 1mm Med-Lat
Slope maintained
5 degree pre op slope unchanged
WB Fem-Tib alignment corrected
Mean preop 7 degrees varus
Mean postop 1 degree varus

13. Patient Specific Jigs and Implants ONLY good Lateral Side Option

14. Tibial fit was much better in patient specific vs legacy implants
1.0 mm mismatch vs 3.3mm mismatch p<.01
Survivorship at mean 36 mos 97% vs 85%

15. PSI Onlay Resurfacing

16. Residual cartilage subjacent to implant removed

17. Holes for implant pegs and cement interdigitation

20. Mobile Bearing… really????
Disadvantages
Huge bone resection
Suboptimal fit
Non anatomic
Advantages
NHS formulary
35+ year history
VCR, pagers, cassettes

21. Robot- an expensive marketing tool???…..
Robot costs >1M $
Newer handhelds are expensive too
Implants are off the shelf
Marked intraop complexity
A “work-around” for PSI Jig and Implant IP

22. Patient Specific Jigs and Implants are the only way to go….
Simpler
Faster
More Accurate
Less Cost
Better Biomechanics
SEEMINGLY BETTER

23. Thank You phildavidsonmd@gmail.com davidsonorthopedics.com