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

No conflicts to report

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

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”

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

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. 310 - 313. 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

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

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

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

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????

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 111.23 preop to 180.61 postop Functional KSS improved from mean 60.39 to 94.51.

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

Patient Specific Jigs and Implants ONLY good Lateral Side Option

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%

PSI Onlay Resurfacing

Residual cartilage subjacent to implant removed

Holes for implant pegs and cement interdigitation

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

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

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

Thank You phildavidsonmd@gmail.com davidsonorthopedics.com