Design of a Rotational Stability Measurement Device For Analysis of ACL Reconstruction

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Design of a Rotational Stability Measurement
DeviceFor Analysis of ACL Reconstruction
University of Pittsburgh Senior Design BioE
1160/1161
Stephanie BechtoldKatie Dillon Kara
Wagner Mentor Thore Zantop, M.D. April 18,
2005
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Goal

• To develop and test a novel device to measure the
  rotational stability of the knee after an
  Anterior Cruciate Ligament (ACL) reconstruction

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ACL anatomy

• Two distinct fiber bundles
• Anteromedial (AM)
• Translational stability
• Posterolateral (PL)
• Rotational stability

www.aclsolutions.com/ images
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Current Reconstruction Methods

• Single bundle
• Restore only the AM bundle
• Susceptible to reinjuries by pivoting
• Double bundle
• Restores both AM and PL bundles
• More anatomically correct

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Devices to Evaluate ACL Reconstruction

• Current devices only measure translational
  stability of the knee
• Double bundle technique creates need for device
  to measure rotational stability
• Evaluate effectiveness of PL bundle reconstruction

http//www.medmetric.com/kt1.htm
http//www.aircast.com
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Problem Statement

• A device is needed to measure the rotational
  stability of the knee
• Comprehensive analysis of reconstruction
  techniques
• An immobilization device is needed to
  comfortably restrict movement in the hip and
  ankle joints
• Ensure pure rotation of the knee is
  measured

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Market Considerations

• Market size
• 16,000 Orthopedic Surgeons (AAOS)
• Predicate Devices
• KT1000 3900
• Rolimeter 850

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Initial Design Considerations

• Adjust boot to keep ankle immobile
• Fix knee at various flexion angles (0, 30, 45,
  60, 90 degrees)
• Comfortably immobilize hip
• Consistently and safely apply known moment
• Collect repeatable data

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Prototype Development- Boot

• Aircast Pneumatic Walker Brace

• Nest of Birds Ascension Technology Corporation,
  Burlington, VT/USA

• Universal force-moment sensor (JR3, Woodland,
  California)

Photos courtesy of Ferguson Lab
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Initial Design Considerations

• Adjust boot to keep ankle immobile
• Fix knee at various flexion angles (0, 30, 45,
  60, 90 degrees)
• Comfortably immobilize hip
• Consistently apply known moment
• Collect repeatable data

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Prototype Development- Hip Brace

• Lateral Decubitus position

• Wheelchair leg rest

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Initial Design Considerations

• Adjust boot to keep ankle immobile
• Fix knee at various flexion angles (0, 30, 45,
  60, 90 degrees)
• Comfortably immobilize hip
• Consistently and safely apply known moment
• Collect repeatable data

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Prototype development

• Redesign of initial prototype
• Patient placed in supine position
• Lower leg horizontal
• Adjustable leg rest
• Knee flexion angle
• Length of femur
• Minimize metal components

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Prototype Fabrication
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Materials Selection

• Constructed of acrylic
• Eliminates metal components
• Minimizes interference with magnetic sensors
• Durable
• Comfortable for patient

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Evaluation of Device

• 4 subjects - at 3 flexion angles
• 5 trials each
• Ensure repeatability
• Goal Range of motion within 1
• Subject reports stability of ankle and hip joints

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Experimental Methods

• Subjective knee evaluation performed by a
  clinician to determine health of knee
• Subject fitted with boot and brace to comfort
• Nest of Birds (NOB) sensors placed on
• Proximal Tibia
• Distal Femur
• Front of Boot

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Experimental Methods

• Lower leg leveled at horizontal
• Creates neutral start position
• Moment applied by clinician (10Nm)
• Range of motion recorded by Nest of Birds

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Experimental Methods
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Sample Results
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Preliminary Results

• Range of Motion, in degrees
• 4 subjects, 5 trials each

 Flexion Angle Subject 1 Subject 2 Subject 3 Subject 4
0 degrees 40.75 1.7 62.20 1.4 43.40 1.5 64.40 1.9
45 degrees 49.60 1.8 52.00 1.0 31.60 0.9 57.00 0.7
90 degrees 37.00 1.6 37.00 0.7 27.20 1.5 54.20 1.8
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Initial Design Considerations

• Adjust boot to keep ankle immobile
• Fix knee at various flexion angles (0, 30, 45,
  60, 90 degrees)
• Comfortably immobilize hip
• Consistently and safely apply known moment
• Collect repeatable data

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Discussion

• Range of motion was repeatable within 2 for all
  subjects
• Subjects reported ease of use and comfort of the
  boot and brace
• Overall apparatus is heavy for operator

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Competitive Analysis

• Our Device
• Strengths
• More comprehensive analysis of ACL reconstruction
• Weaknesses
• Complex design
• Higher cost

• Predicate Devices
• Strengths
• Lightweight
• Simple design
• Weaknesses
• Limited analysis of reconstruction techniques

• Race for first to market
• Competition to develop similar device

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Constraints limiting Phase I testing

• IRB approval
• Create baseline data for normal subjects
• Overhead cost of measurement devices

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Quality System Considerations

• Class I device non-invasive
• Human factors
• Biocompatibility
• Ease of use for clinician
• Patients Comfort
• Ethical issues
• Broad range of normal subjects
• Reduce cost

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Future

• Streamline design
• Minimize cost
• Lower weight of apparatus
• Testing on reconstruction patients
• Evaluate effectiveness of technique
• Possible combination device based on KT1000 or
  Rolimeter
• To measure both translational and rotational
• stability in the same device

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Acknowledgements

• Kevin Bell M.S.
• Volker Musahl M.D.
• Ryan Costic M.S.
• Larry Herman
• Department of Bioengineering
• Drs. Hal Wrigley and Linda Baker

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IKDC form

• Standard, subjective knee evaluation
• Patient
• History of injury
• Symptoms
• Activity Level
• Clinician
• Translational stability evaluated using KT1000 or
  rolimeter
• Subjective evaluation of rotational stability

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Background

• 100,000 ACL reconstructions per year
• 6th most common orthopedic procedure in the US
• Debate over best method
• Single vs. double bundle
• Complex anatomy
• AM bundle - translation
• PL bundle - rotation

Courtesy of Ferguson Lab
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Work Breakdown

• Kara Wagner
• Background research, contact with machine shop
• Katie Dillon
• Testing
• Stephanie Bechtold
• Solidworks prototype
• Everyone
• Design History File, SBIR

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Milestones

• Initial meeting with mentor October 2004
• Initial draft of design history file December
  8, 2004
• Initial draft of SBIR December 17, 2004
• Ordered materials First week of March 2005
• Completed Solidworks Third week of March
• Prototype Completed Last week of March
• Preliminary testing First week of April