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APEX Knee Design Rationale

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Presentation on theme: "APEX Knee Design Rationale"— Presentation transcript:

1 APEX Knee Design Rationale

2 Design Intent Anatomic components Insert/femur size matching
Asymmetric femurs and trays Symmetric inserts Insert/femur size matching True posterior referencing femoral design Improved sizing for better fit Enhanced flexion

3 Design Intent Both cruciate sparing and cruciate sacrificing inserts
Dome patella Cemented and cementless components Simplified instrumentation

4 Femoral Components Six “basic” sizes Half sizes 2 + and 3+ Size M/L
A/P 1 58 54 2 62 2 + 60 3 66 3+ 64 4 70 5 75 6 80

5 SINGLE RADIUS

6 Plus Sizes - If Size 4 is too wide, switch to a 3+ femur
FEMORAL COMPONENTS Plus Sizes - If Size 4 is too wide, switch to a 3+ femur Same bone cuts Narrower Thinner Flange 3+ Uses Size 3 insert Same logic for Size 3 and 2 +

7 13 of 59 Knees were + sizes (22%) 12 of 13 + sizes were Female (92%)
Femur Size Total Male Female 1 - 2 8 2+ 5 3 18 17 3+ 7 4 6 10 59 TOTAL 18 TOTAL 41 TOTAL 13 of 59 Knees were + sizes (22%) 12 of 13 + sizes were Female (92%)

8 HIGH FLEX DESIGN - Geometry allows up to 155 degrees of flexion - Larger posterior condyle maintains low contact stress - Design allows knee to rest in posterior third of tibia

9 PATIENTS SUBCONSCIOUSLY RECOGNIZE THESE LIMITS FROM DESIGNS
Preferred Range called comfort range = stability Semi Comfort Range= muscular effort stability- positional Extreme Range= avoidance unstable activities- check reins Most important stability is mid-stance or navigating stairs. Mid-stance is a function of design of the prosthesis.

10 Femoral Components Plus Sizes If Size 4 is too wide, Downsize to 3+
Same bone cuts Narrower Thinner Flange 3+ Uses Size 3 insert Same logic for Size 3 and 2 +

11 Femoral Components Patella track is 6º 3 Radii rollback
Heel strike to toe off Flexion (up to 120º) Deep Flex (up to 145º) 4º anterior flange Posterior referencing Constant posts Constant posterior chamfer

12 CONDULAR CONTACT - Rounded femoral condyle accommodates varus-valgus lift found in eccentric loading. - Matched congruent tibial topography accommodates knee kinematics with low contact stresses. - Single Radius allows increased contact area and consistent stability w/o post and cam.

13 No Anterior Notch Resection

14 Patella 30 mm spherical dome Three pegs 29, 32, 35, 38 mm Ø
8 mm and 10 mm thick

15 MECHANICS OF PATELLA FUNCTION

16 PATELLA FLANGE - Flange is very generous but thin for patella tracking
- Designed with deep and wide groove set at 6 degrees - Because of rollback- > quad lever arm increased and improved for leverage in flexion where > stress.

17 PATELLA FEATURES AND BENEFITS
- Congruent contact reduces poly contact stress - Reduction of wear due to patella femoral groove - Improved mechanics due to wide patella flange - Improved mechanics due to decrease in quad lever arm - Design of Apex allows rollout of femur to engage patella in deeper flexion

18 SUPERIOR PATELLA TRACKING

19 Patella Tracking Motion Analysis

20 Tibial Components Two designs will eventually be offered
“Conventional” UHMWPE insert (available) “Metal on Metal” orientable insert (in development) Common philosophy Asymmetric, keeled CoCr tray Symmetric inserts Inserts matched to femurs for optimized contact stress

21 Tray (Common Features)
Size M/L A/P (Med) A/P (Lat) 1 62 41 40 2 66 44 42 3 70 46 4 75 50 47 5 80 53 6 85 56 Seven sizes Asymmetric about sagittal plane 1 mm deep pocket Grit blast CoCr alloy on inferior surfaces

22 Tray (Common Features)
Tapered post located approximately 60% A/P (closer to anterior edge) Two posteriorly swept keels Keel dimensions are shared by the size 2/3, 4/5, and 6/7 trays. Post length increases with size (40mm, 45 mm, 54 mm) 4º posterior slope

23 ASYMMETRIC BASEPLATE - Replicates the resected anatomical shape of tibia. - Maximizes coverage without overhang common in symmetrical designs. - Baseplate accepts all sizes of tibia inserts because of dovetail groove.

24 WINGED KEEL GEOMETRY - 4 Degree slope to avoid anterior tibial contact. - Swept rounded keel for stability and non contact with endosteal cortex. - Resist rotational forces due to posterior inclination of keel.

25 4 DEGREE POSTERIOR SLOPE

26 DOVETAIL TRAYS Two rails constrain the insert
Locking peg prevents A/P motion Any insert fits on any tray Slide loading for ease of assembly Taper lock peg resists backing out

27 Dovetail inserts All rails are the same width and distance
Central locking peg is tapered for locking and to contain the UHMWPE

28 Inserts (Common Features)
Standard and “Ultra” configurations 10, 12, 14, 16, 18, 20mm thickness Inserts match femoral component EtO Sterilization X-link Poly 2010

29 Optimized Contact Stress
Peak 13.4 MPa Peak 12.5 MPa Contact stresses on the Apex Modular CR (left) and Ultra (right) inserts, 0° flexion.

30 CONTACT STRESSES Yield stress for UHMWPE = 22.5 Mpa

31 Revision Tibial Components/Femoral Components
FUTURE DEVELOPMENTS Revision Tibial Components/Femoral Components

32 MOM TKA Variable Rotation and Mobile Bearing
FUTURE DEVELOPMENTS MOM TKA Variable Rotation and Mobile Bearing

33 MOM Inserts (In Development)
Factory assembled poly/metal sandwich Cryogenic assembly Highly polished inferior surface Fixed or rotating application

34 MOM Trays Rotate insert on tray to proper alignment
Lock in position using press fit peg ± 5 degrees on same size tray Future rotating platform


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