stiehl jb. design factors influencing rom in tka
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Design Factors Influencing Range of Motion in TKA
Design Factors Influencing Range of Motion in TKA
James B. Stiehl, MD
Medical College of Wisconsin
Milwaukee, Wisconsin
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Factors Determining ROM in TKAFactors Determining ROM in TKA
• Preoperative ROM and body habitus
• Prior surgery or trauma
• Surgical technique• Postoperative pain and
scarring problems
• Prosthetic Design
130
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Patient Factors: ObesityPatient Factors: Obesity
• Flexion > 120°; 7% obese
• Flexion 101° to 119°; 28% obese
• Flexion < 100°; 78% obese
• Shoji,et.al. Orthopaedics, 1990
• Flexion>130 Kinemtics Driven by Thigh Contact
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Active vs Passive Range of Motion in TKA
Active vs Passive Range of Motion in TKA
• Weight bearing flexion < Passive flexion in Normal, PCR, PS (P<.045)
• Active Flexion: Normal-135°; PCR-103°;PS-113°
• PS > PCR Active Weight Bearing (P<.025)
Dennis, et.al., Jl Arthroplasty,1998
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Balanced Flexion GapBalanced Flexion Gap
• Posterior condylar reference (0° ER): 120° Preop to 100° Postop (PCR)
• Posterior condylar reference (~3° ER): 115° Preop to 112° Postop (PS)
• Laskin, et.al., Jl Arthroplasty, 1995
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Tibia Cut First Surgical Technique Tibia Cut First Surgical Technique
• Anterior Femoral Cortical Reference
• Flexion Space: Tension Adjustment
• Distal Femoral Cut Last
• Standard Revision Arthroplasty Method
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Kinematic “Conflict”, circa 2007Kinematic “Conflict”, circa 2007
• Absent ACL Causes Loss of “Rollback”• True for Unicondylar, Bicruciate, Cruciate
Retaining, and “Total Condylar” Rotating Platform
• Anterior Translation exaggerated by Flexion Laxity
• ? Effect of Joint Line Elevation, but may tend to tighten extensor mechanism
• PS drives “roll back” and higher flexion Dennis, et.al., Knee Society, 2003
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LCS Design Issues for ROMLCS Design Issues for ROM
• Neutral to Anterior Starting Position
• Early “Rollback” for BCR, PCR, and RP
• “Slide Forward” seen in deep flexion in virtually all cases (120 Limit)
• Lack ACL Function• Stiehl, et.al. “LCS Moble
Bearing TKA”,2002, Springer
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LCSPS Design FlawsLCSPS Design Flaws
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LPS High Flex TKALPS High Flex TKA
• Posterior Stabilized Design: “ROLLBACK”
• Augmented Posterior Condyles: + 2MM
• Patellar Cutout to prevent impingment
• Spine/Cam: Low contact point, Higher spine, Extended articulation posterior
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LPS Design ConsiderationsLPS Design Considerations
Longer Cam; Posterior Condyle 2mm >
LPS High Flex LPS
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Impingement
Patellar ImpingementPatellar Impingement
LPS
LPS High Flex
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LPS High Flex Mobile ROMLPS High Flex Mobile ROM
• 102 TKA; Age 66 ave.(43 to 80); Wt- 72 Kg ( 36 to 110)
• Varus Deformity: Ave 9° (Range 4° to 20°)• Valgus Deformity: Ave 6°(Range 1° to 11°)• Postop Femorotibial Angle: 2° Valgus
(Range 1° to 5°)• Preoperative Flexion: 120° ( 90° to 140°)• Postoperative Flexion: 131° (90° to 150°)
Argenson, et.al., ISK Fall Meeting, 2003
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Literature Review: PS vs PS FlexLiterature Review: PS vs PS Flex
Author N PS PS High Flex SD
Bin, et.al. 180 124 129 <.05
Huang, et.al. 50 126 138 <.05
Kim, et.al. 50* 135 138 =0.41
Weeden, et.al. 50 120 135 <.05
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Kinematics of LPS High FlexKinematics of LPS High Flex
• Cadaver Test: (n=13)
• Quads force 400 N; Hamstring force 200 N
• Spine/Cam engagement: 80 to 135• Soft Tissues Active >135• Medial Rollback: 2.3 mm
• Lateral Rollback: 3.2 mmLi, et.al. JBJS 86A: 1721
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Kinematics of LPS High FlexKinematics of LPS High Flex
• 20 Subjects; invivo fluoroscopy
• Weight Bearing Deep Knee Bend:125• Average 4.4 millimeters Rollback
• Average 4.9 Internal RotationArgenson, et.al. J Biomechanics 38: 277, 2005
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LPS High Flex Mobile ResultsLPS High Flex Mobile Results
150° Passive Flexion
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LPS High Flexion SittingLPS High Flexion Sitting
9 Inch Stool, >135° Flexion
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LPS High Flex- Down StairsLPS High Flex- Down Stairs
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LCS Versus LPS High Flex in Passive Flexion
LCS Versus LPS High Flex in Passive Flexion
Left- LPS High Flex- 115 Right- LCS - 105
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What Do I Tell My Patients?What Do I Tell My Patients?
• Preoperative Range of Motion of 90° probably improves 15-25°
• Stair function, sitting, and exercycle requires > 110° Flexion
• Certain patients have painful knees and will not improve (about 1 of 20)
• LPS High Flex, properly done, may flex 130° to 140° in many cases!!
• This may be best in patients over 65-70.
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Is There A Liabilty to High Flexion in TKA
Is There A Liabilty to High Flexion in TKA
• Yes, Yes, and YES!!!
• The mechanical forces in high flexion are EXTREME, 40-60 mPascals on Poly
• Forces may exaggerate post wear and potential failure
• Chronic synovitis and anterior knee pain seem to be more common in these patients. (Now AVOID Patella resurface)
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CONCLUSIONCONCLUSION
• PostOP Flexion is multifactorial
• Surgical Technique and Design are important
• PS Option Best in Low Demand; ??? High forces on poly in flexion
• LPS High Flex offers predictably higher flexion!!
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LPS High Flex WalkingLPS High Flex Walking
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