Influence of Knee Brace Design on Joint Movements

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Influence of Knee Brace Design on Joint Movements

• Tyler Dubetz
• Faculty Mentor Dr. Janet Ronsky

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Outline

• 1.0 Introduction
• 2.0 Methods
• 3.0 Results
• 4.0 Discussion
• 5.0 Conclusion

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1.0 Introduction

• 1.1 Purpose
• 1.2 Scope

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1.1 Purpose

• Develop a testing method that allows the
  distinction between 2 types of displacement
• Examine the control of anterior tibial
  displacement by a custom functional brace, the
  Clynch Competitive Edge.

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1.2 Scope

• Physical blocking of limb segments
• Comparative results, not to definitively
  determine whether braces work or not

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2.0 Methods

• 2.1 Surrogate Model Design
• 2.2 Testing Systems
• 2.3 Testing Protocol
• 2.4 Data Analysis

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2.1 Surrogate Model Design

• Exact external geometry of the leg
• Cast of subjects leg
• Pour liquid foam inside the cast to match the
  external geometry

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2.1 Surrogate Model Design

• Some internal geometry of the leg
• Inner structure (rigid foam) machined to simulate
  tibial ridge

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2.1 Surrogate Model Design

• Soft-tissue substitute that matches the stiffness
  of contracted muscle
• Stiffness of contracted muscle in athletes 3.28
  N/mm (Liu et al.)
• Stiffness of Liquid Pudgee foam (Dynamic Systems
  Inc.) 3.52 N/mm

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2.1 Surrogate Model Design

• Ability of knee joint to move freely in the
  sagittal plane
• Sectioned the leg at the level of the tibial
  plateau (and 1 inch above)
• Thigh section fixed at both proximal and distal
  ends
• Shank section allowed to rotate about a
  horizontal axis at the ankle

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2.1 Surrogate Model Design
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2.2 Testing Systems

• MTS (biomechanics), 1 kN load cell, sampling
  frequency 4 Hz
• 4 camera motion capture system (Falcon, Motion
  Analysis Corp.), sampling frequency 60 Hz

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2.2 Testing Systems
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2.2 Testing Systems
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2.2 Testing Systems
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2.3 Testing Protocol

• All trials at 0 degrees of flexion
• 5 trials without brace, ramp _at_ 0.3175 mm/s up to
  50 mm
• 10 trials with brace, 5 cycles up to 40 N to seat
  brace, ramp _at_ 0.3175 mm/s up to 400 N, straps
  re-tensioned to 15 lb before each trial
• 2 trials with brace, ramp _at_ 1 mm/s
• 5 trials without brace same as 1st 5 trials

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2.4 Data Analysis

• Non-brace trials friction as a function of
  displacement
• Used to subtract forces not actually supported by
  brace
• Plot vertical displacement of marker at tibial
  plateau and vertical displacement of marker at
  centre of hinge vs. load
• Fit 6th order polynomial

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3.0 Results
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3.0 Results

• Calculated displacements at 400 N
• Centre of knee brace hinge 8.25 mm
• Tibial plateau 14.8 mm
• Results from Liu et al.
• 400 N, tibial plateau
• Townsend brace 22.4 mm
• MKS II brace 21.2 mm

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4.0 Discussion

• Clynch Competitive Edge brace controls ATD to a
  minimum at physiological levels of force
• Displacement of brace is 56 of total
  displacement

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4.0 Discussion

• Limitations
• Number of braces tested
• Comparing results from different surrogate leg
  models, different degrees of flexion

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5.0 Conclusions

• Clynch CE brace can withstand forces likely to
  occur in-vivo and control ATD to a minimum
• Surrogate model gives an accurate interaction
  between brace and leg, enabling the measurement
  of displacement of leg relative to brace
• Testing more braces would greatly strengthen
  conclusions drawn from this project

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Acknowledgements

• Markin-Flanagan/USRP program
• Dr. Janet Ronsky
• Dr. James Harder
• George Clynch Clynch Technologies Inc.
• Ion Robu