Is Posterior Stabilized Needed in TKA

Is Posterior Stabilized Needed in TKA

James B. Stiehl, MD

Medical College of Wisconsin

Milwaukee, Wisconsin

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

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

INVIVO FLUROROSCOPYINVIVO FLUROROSCOPY

Lat condyle, normal Lateral Condyle PCR-TKA

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!!

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

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

Extensor Mechanism Power Curve

Extensor Mechanism Power Curve

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

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

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

PS for DeformityPS for Deformity

7 Varus

16 Varus

16 Varus 0 Varus

Case: 52 YO FemaleCase: 52 YO Female

Severe Distal Femur Fracture with 10° Varus Deformity; Flexion

Final Result: Free NavigationFinal Result: Free Navigation

Mechanical Axis: 0° !!!

Final Result: Free NavigationFinal Result: Free Navigation

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.

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

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

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

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

-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

-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

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

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

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

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