APEX Knee Design RationaleAPEX Knee Design Rationale

Design IntentDesign Intento Anatomic componentsAnatomic components

Asymmetric femurs and traysSymmetric inserts

o Insert/femur size matchingInsert/femur size matchingo True posterior referencing femoral designTrue posterior referencing femoral designo Improved sizing for better fitImproved sizing for better fito Enhanced flexionEnhanced flexion

Design IntentDesign Intento Both cruciate sparing and cruciate sacrificing Both cruciate sparing and cruciate sacrificing

inserts inserts o Dome patellaDome patellao Cemented and cementless componentsCemented and cementless componentso Simplified instrumentationSimplified instrumentation

Femoral ComponentsFemoral Componentso Six “basic” sizesSix “basic” sizeso Half sizes 2 + and 3+Half sizes 2 + and 3+

Size M/L A/P

1 58 54

2 62 58

2 + 62 60

3 66 62

3+ 66 64

4 70 66

5 75 70

6 80 75

SINGLE RADIUSSINGLE RADIUS

FEMORAL COMPONENTSFEMORAL COMPONENTS

o Plus Sizes - Plus Sizes - If Size 4 is too wide, switch to a 3+ femurIf 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 +

13 of 59 Knees were + sizes (22%)12 of 13 + sizes were Female (92%)13 of 59 Knees were + sizes (22%)12 of 13 + sizes were Female (92%)

Femur Size Total Male Female

1 0 - -

2 8 0 8

2+ 5 0 5

3 18 1 17

3+ 8 1 7

4 8 6 2

5 10 8 2

6 2 2 0

59 TOTAL 18 TOTAL 41 TOTAL

HIGH FLEX DESIGNHIGH FLEX DESIGN

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

PATIENTS SUBCONSCIOUSLY RECOGNIZE THESE

LIMITS FROM DESIGNS

PATIENTS SUBCONSCIOUSLY RECOGNIZE THESE

LIMITS FROM DESIGNS

Preferred Range called comfort range = stabilityPreferred Range called comfort range = stabilitySemi Comfort Range= muscular effort stability- Semi Comfort Range= muscular effort stability- positionalpositionalExtreme Range= avoidance unstable activities- Extreme Range= avoidance unstable activities- check reinscheck reinsMost important stability is mid-stance or navigating Most important stability is mid-stance or navigating stairs.stairs.Mid-stance is a function of design of the prosthesis. Mid-stance is a function of design of the prosthesis.

Femoral ComponentsFemoral Componentso Plus SizesPlus Sizes

If Size 4 is too wide,Downsize to 3+

Same bone cutsNarrowerThinner Flange3+ Uses Size 3 insert Same logic for Size 3 and 2 +

Femoral ComponentsFemoral Componentso Patella track is 6ºPatella track is 6ºo 3 Radii rollback3 Radii rollback

Heel strike to toe offFlexion (up to 120º)Deep Flex (up to 145º)

o 4º anterior flange4º anterior flangeo Posterior referencingPosterior referencing

Constant postsConstant posterior chamfer

CONDULAR CONTACTCONDULAR CONTACT

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

No Anterior Notch ResectionNo Anterior Notch Resection

PatellaPatellao 30 mm spherical dome30 mm spherical domeo Three pegsThree pegso 29, 32, 35, 38 mm Ø29, 32, 35, 38 mm Øo 8 mm and 10 mm thick8 mm and 10 mm thick

MECHANICS OF PATELLA FUNCTIONMECHANICS OF PATELLA FUNCTION

PATELLA FLANGEPATELLA FLANGE

- Flange is very generous but thin for patella tracking- Flange is very generous but thin for patella tracking- Designed with deep and wide groove set at 6 degrees- Designed with deep and wide groove set at 6 degrees- Because of rollback- > quad lever arm increased and - Because of rollback- > quad lever arm increased and

improved for leverage in flexion where > stress. improved for leverage in flexion where > stress.

PATELLA FEATURES AND BENEFITSPATELLA FEATURES AND BENEFITS

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

SUPERIOR PATELLA TRACKINGSUPERIOR PATELLA TRACKING

Patella Tracking Motion AnalysisPatella Tracking Motion Analysis

Tibial ComponentsTibial Componentso Two designs will eventually be offeredTwo designs will eventually be offered

“Conventional” UHMWPE insert (available)“Metal on Metal” orientable insert (in development)

o Common philosophyCommon philosophyAsymmetric, keeled CoCr traySymmetric insertsInserts matched to femurs for optimized contact stress

Tray (Common Features)Tray (Common Features)o Seven sizesSeven sizeso Asymmetric about sagittal Asymmetric about sagittal

planeplaneo 1 mm deep pocket1 mm deep pocketo Grit blast CoCr alloy on Grit blast CoCr alloy on

inferior surfacesinferior surfaces

Size M/L A/P (Med) A/P (Lat)

1 62 41 40

2 66 44 42

3 70 46 44

4 75 50 47

5 80 53 50

6 85 56 53

Tray (Common Features)Tray (Common Features)o Tapered post located Tapered post located

approximately 60% A/P approximately 60% A/P (closer to anterior edge)(closer to anterior edge)

o Two posteriorly swept keelsTwo posteriorly swept keelso Keel dimensions are shared Keel dimensions are shared

by the size 2/3, 4/5, and 6/7 by the size 2/3, 4/5, and 6/7 trays. trays.

o Post length increases with Post length increases with size (40mm, 45 mm, 54 mm) size (40mm, 45 mm, 54 mm)

o 4º posterior slope4º posterior slope

ASYMMETRIC BASEPLATEASYMMETRIC BASEPLATE

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

WINGED KEEL GEOMETRYWINGED KEEL GEOMETRY

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

4 DEGREE POSTERIOR SLOPE4 DEGREE POSTERIOR SLOPE

DOVETAIL TRAYSDOVETAIL TRAYS

o Two rails constrain the Two rails constrain the insertinsert

o Locking peg prevents A/P Locking peg prevents A/P motionmotion

o Any insert fits on any trayAny insert fits on any trayo Slide loading for ease of Slide loading for ease of

assemblyassemblyo Taper lock peg resists Taper lock peg resists

backing outbacking out

Dovetail insertsDovetail insertso All rails are the same width and distanceAll rails are the same width and distanceo Central locking peg is tapered for locking and Central locking peg is tapered for locking and

to contain the UHMWPEto contain the UHMWPE

Inserts (Common Features)Inserts (Common Features)o Standard and “Ultra” Standard and “Ultra”

configurationsconfigurationso 10, 12, 14, 16, 18, 10, 12, 14, 16, 18,

20mm thickness20mm thicknesso Inserts match femoral Inserts match femoral

componentcomponento EtO SterilizationEtO Sterilizationo X-link Poly 2010X-link Poly 2010

Optimized Contact StressOptimized Contact Stress

Contact stresses on the Apex Modular CR (left) and Ultra (right) inserts, 0° flexion.

Peak 13.4 MPa Peak 12.5 MPa

CONTACT STRESSESCONTACT STRESSES

Yield stress for UHMWPE = 22.5 Mpa

FUTURE DEVELOPMENTSFUTURE DEVELOPMENTS

Revision Tibial Components/Femoral Revision Tibial Components/Femoral ComponentsComponents

FUTURE DEVELOPMENTSFUTURE DEVELOPMENTS

MOM TKA Variable Rotation and Mobile MOM TKA Variable Rotation and Mobile BearingBearing

MOM Inserts (In Development)MOM Inserts (In Development)

o Factory assembled Factory assembled poly/metal sandwichpoly/metal sandwich

o Cryogenic assemblyCryogenic assemblyo Highly polished inferior Highly polished inferior

surfacesurfaceo Fixed or rotating Fixed or rotating

applicationapplication

MOM TraysMOM Trayso Rotate insert on tray to Rotate insert on tray to

proper alignmentproper alignmento Lock in position using Lock in position using

press fit pegpress fit pego ± 5 degrees on same ± 5 degrees on same

size traysize trayo Future rotating platformFuture rotating platform