stiehl jb. is ps needed in tka
TRANSCRIPT
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Is Posterior Stabilized Needed in TKA
Is Posterior Stabilized Needed in TKA
James B. Stiehl, MD
Medical College of Wisconsin
Milwaukee, Wisconsin
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Posterior Stabilized Advantages and Problems
Posterior Stabilized Advantages and Problems
• Enforced femoral rollback
• Greater range of motion
• Greater extensor mechanism lever
• Optimal for more difficult deformity
• Requires tight gap stability and correct prosthetic alignment
• Not good for high contact (Innex, LCS)
• Spine/Cam source of wear
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KINEMATICS OF TOTAL KNEE ARTHROPLASTY
KINEMATICS OF TOTAL KNEE ARTHROPLASTY
• Posterior Femorotibial Contact in Extension
• Paradoxical Anterior Contact Translation
• Lateral Condyle Liftoff• ACL Deficient
Kinematics Stiehl, et.al
JBJS(B)1995
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INVIVO FLUROROSCOPYINVIVO FLUROROSCOPY
Lat condyle, normal Lateral Condyle PCR-TKA
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Fluoroscopic Kinematic Analysis of TKA: Conclusions
Fluoroscopic Kinematic Analysis of TKA: Conclusions
• Exaggerated and abnormal motions such as greater medial AP sliding TYPICAL!!
• Rotation can be up to 10° Internal/External• Condylar Liftoff up to 3-4 mm in “good” TKA• Frontal plane translation important, confirms
multidirectional sliding on polyethylene• TKA Design and Clinical Performance must
accommodate these biomechanical parameters!!• Kinematics are SURGEON SPECIFIC!!
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What About Wear in Mobile Bearings?
What About Wear in Mobile Bearings?
• 206 LCS MB vs 619 Fixed Bearings
• M B had less delamination, cold flow and abrasion(p<.01
• MB ususally oxidized poly
• MB measured wear estimated at .05 mm/year
Collier,Mayor,2002
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Forward Body Lean on StairsForward Body Lean on Stairs
• Extensor Moment Weakness in TKA:
• 19% Posterior Cruciate Sacrifice
• 15 % Posterior Cruciate Retention
• 12% Posterior Cruciate Substitution
Mahoney, Jl Arthroplasty,1994
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Extensor Mechanism Power Curve
Extensor Mechanism Power Curve
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Anterior Femorotibial Translation in TKA
Anterior Femorotibial Translation in TKA
• Anterior translation decreases levering effect of the patella
• Occurs with posterior cruciate retention
• PS 4-5 mm rollback reduces
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Mechanics of Joint Line Elevation: PCR vs PS
Mechanics of Joint Line Elevation: PCR vs PS
• PS: elevation of joint line 5-7mm
• PCR: slight elevation of joint line, anterior translation causes significant PF contact elevation
• Outcome: ???Wash• Stiehl, J of Arthroplasty
2001
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Contact Stress and High FlexionContact Stress and High Flexion
• Morra, et.al. 135 Flexion, 3100N- 32MPa• Chapman, et.al. 90 to 135, 3600N- 22 to
36MPa• Morra, et.al. Spine/Cam articulation, 279N
- 32 MPa• Nakayama, et.al. Spine/Cam articulation,
500 N, 90 to 150 flexion- 22-34MPa• Polyethylene fails at 30 Mpa• ???? Realistic For Invivo Loading
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PS for DeformityPS for Deformity
7 Varus
16 Varus
16 Varus 0 Varus
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Case: 52 YO FemaleCase: 52 YO Female
Severe Distal Femur Fracture with 10° Varus Deformity; Flexion
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Final Result: Free NavigationFinal Result: Free Navigation
Mechanical Axis: 0° !!!
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Final Result: Free NavigationFinal Result: Free Navigation
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Level 4 Outcome DataLevel 4 Outcome Data
• Non-randomized Control Retrospective Outcome Studies (??Designer)
• Literature Review:• 10-23 Year Follow-up• 4-13% Revision Rate• Survivorship Rates: 85% to 95%• No advantage: PS, CR, Measured
Resection, Tibia Cut First, etc• Most studies lack Control Group,
Statistical Power or careful study design, >80% followup, etc.
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Osteolysis in PS TKAOsteolysis in PS TKA
• 105 PS TKA’s, 5-8 year followup• Modular Base Plates• Osteolysis found in 16%• Two revisions were found to have
backsided wear and tibial post wear due to impingement
O’Rourke, et.al. JBJS 84A: 1362
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Tibial Post Wear in PS TKATibial Post Wear in PS TKA
• 23 TKA Revisions of PS TKA
• Median followup 3.5 years ( 2.3 to 107 mo)
• 40% had Post Deformation, Adhesive Wear, Burnishing
• Wear: Medial, lateral and anterior surfaces
• Two failures due to post failurePuloski, Rorabeck, et.al. JBJS
83A: 390
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Recommendations for TKARecommendations for TKA
• Implant Design: LCS RP vs LPS High Flex
• Surgical Technique: Tibia Cut First
• Goals: 0 Mechanical Axis; <3 Gaps
• Mobile Bearing: High Performance, Healthy and Under Age 65
• PS: Offers better flexion; easier in cases with deformity! Best option for patient over age 70
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LCS Rotating Platform vs Posterior Stabilized 3D Analysis
LCS Rotating Platform vs Posterior Stabilized 3D Analysis
• Invivo Weight Bearing Fluoroscopy
• 10 Patients• Automated 3D
Computer Model Fitting
• Medial/Lateral Condyle Sagital Plane Evaluation
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-15
-10
-5
0
5
10
AP Position (mm) [- posterior, + anterior]
0
30
60
90
Lateral Medial
-15
-10
-5
0
5
10
AP Position (mm) [- posterior, + anterior]
0
33
66
100
Lateral Medial
Gait
Deep Knee Bend
LCS ROTATING PLATFORMLCS ROTATING PLATFORMLCS ROTATING PLATFORMLCS ROTATING PLATFORM
• Average position midline during stance phase gait
• Deep Knee Bend: 0° to 60°- Medial 1.2 mm anterior; Lateral 4.0 mm posterior 60° to 90° - Medial 1.2 mm anterior; Lateral 1.0 mm anterior
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-15
-10
-5
0
5
10
AP Position (mm) [- posterior, + anterior]
0
33
66
100
Lateral Medial
Gait
-15
-10
-5
0
5
10
AP Position (mm) [- posterior, + anterior]
0
30
60
90
Lateral Medial
Deep Knee Bend
LCSPS ROTATE PLATFORMLCSPS ROTATE PLATFORMLCSPS ROTATE PLATFORMLCSPS ROTATE PLATFORM• Gait: Positions are
constant from stance to swing phase
• DKB: Medial condyle –0.5 mm to –2.5 mm Lateral condyle -0.6 mm to –6.5 mm
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LCS RESULTS: CONDYLAR LIFTOFF
• 80% Significant Liftoff (0.75 mm)• 50% Liftoff - Heelstrike, 66% ,
Toeoff• 50% Medial and Lateral Condyle
Liftoff• Greatest Medial Liftoff: 2.12 mm• Greatest Lateral Liftoff: 3.53 mm
Stiehl, Jl Arthroplasty 1999
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Coronal Plane LiftoffCoronal Plane Liftoff
• LPS High Flex- 6• Insall design allows
both liftoff and medial translation
• LCS PS- fixed with 2 of liftoff and minimal medial translation
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Disadvantages: PS High FlexDisadvantages: PS High Flex
• ??? Anterior Knee Pain (?Unresurface, Gender)• ??? Increased Polyethylene Contact Stress in High
Flexion• ??? Chronic effect of asymetrical loads on late
loosening• Designs: posterior femoral condyle extension,
patellar tendon cut out, posterior tibia flat, must not have anterior tibial impingement, ??? Poor for mobile bearing
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Posterior Stabilized Disadvantages
Posterior Stabilized Disadvantages
• Wear: Spine/Cam• Rotational Mismatch (needs mobile)• Limb mal-alignment• Ligamentous instability• Limited area contact from design
• Joint Line Elevation• ??? Ligament Stretching over time
CallaghanRorabeckHamelynck