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

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

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

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

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

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

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

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

LCSPS Design FlawsLCSPS Design Flaws

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

Impingement

Patellar ImpingementPatellar Impingement

LPS

LPS High Flex

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

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

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

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

LPS High Flex Mobile ResultsLPS High Flex Mobile Results

150° Passive Flexion

LPS High Flexion SittingLPS High Flexion Sitting

9 Inch Stool, >135° Flexion

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

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.

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)

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!!

LPS High Flex WalkingLPS High Flex Walking

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