New Method for Rapid AFO Production

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New Method for Rapid AFO Production

• Group 9
• Team Members
• Ian Pearson
• Corinne Pascale
• Jeffrey Bayers
• Mentor
• Carl Sullivan C.O. ABC Certified Orthotist
• Website http//userfs.cec.wustl.edu/cnp1/bme401/
  

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Background

• Ankle-foot orthotics (AFOs) are rigid casts used
  to correct drop-foot by enhancing the structural
  integrity of the foot and lower leg.
• Current method
• Patient mold ? Plaster ? Thermoplastic ?
  Cutting/Smoothing ? Straps

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Need

• AFO production uses time and materials at a rate
  that is inconvenient for both the fabricators and
  the patients
• Patients should be able to meet with an orthotist
  and pick up their completed AFO on the same day
  to minimize physical dysfunction and commute
  expenses
• Removing the plaster-casting step from AFO
  fabrication would mitigate both of these issues
• METHOD

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Design Requirements

• All design requirements are measured relative to
  the current predominant method of AFO fabrication
• Shorten duration of start-to-finish fabrication
• Reduce required materials (plaster)
• Low-tech easy laboratory implementation
• Inexpensive
• Disposable patient-contact materials
• Maintain patient physical and psychological
  comfort
• Minimal training required
• AFO quality current method

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Selected Design Concept

• Broad concept Mold-to-Mold (safer, easier)
• Specific method STS Socks
• What this means
• A thin, pliable material (STS Sock) is molded to
  the patients lower leg and foot. After
  hardening, it is removed, reinforced, and wrapped
  with pliable high-temperature thermoplastic.
  After cooling, the hardened thermoplastic mold is
  cut from the sock and smoothed/polished.

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Chosen Design

• We designed a method, not a device!
• The end result is the same
• The problematic steps have been removed and
  replaced with more effective procedures
• 2 Components
• Materials
• Procedure

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Design Details Materials

• Primary Material Cast

• Additional Materials

• STS Sock
• Primary Materials AFO
• 3/16 polypropylene

• Plastic bag
• Rubber tube
• Water bath
• Specialty scissors
• Sand
• Steel tube
• Stockings
• Duct tape/staples
• Electrical tape
• Plaster
• Modeling clay
• Vacuum Pump
• Marker
• Cast cutter
• Sander
• Strap

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Design Details Primary Materials

• STS Socks
• Spandex, fiberglass, water curable polyurethane
  resin
• 17 long
• 1/16 thick
• Roll on like ordinary socks
• No wrinkles
• Excellent conformity
• Porous
• Sets rapidly (lt 5 minutes)
• Info and picture from http//www.stssox.com/tubul
  ar_cast_sock.asp

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Design Details Primary Materials

• STS Socks
• Easily applied in multiple layers
• No thermal layer necessary
• Vacuum pressure applied in center (same as
  standard method)
• Textured surface allows for easy application of
  clay
• No casting room required
• Shelf life of 1 year

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Design Details Primary Materials

• Polypropylene
• Clear thermoplastic
• 3/16 thick
• 12x24 sheets
• Becomes soft at high temperatures (200C)
• Hardens at low temperatures
• High tensile strength

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Design Details Safety

• Mostly low risk
• ½ of moderate risks are machine damage
• High risk factors
• Burning or cutting self when working with
  thermoplastic
• Cutting self when removing the thermoplastic from
  the mold
• Abrading self when grinding the AFO
• But all of the high risks also apply to the
  current method!

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Design Details Safety

• The high risk factors (burning cutting) can all
  be easily avoided with training, practice, and
  the use of protective thermal gloves as well as
  goggles

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Analytic Efforts

• We conducted multiple experimental AFO
  fabrications to explore
• -Speed of fabrication
• -Specificity
• -Design limitations

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Analytic Efforts Time/Specificity

• Conducted three time trials to determine average
  time needed for fabrication.
• Result of three trials 92 minutes on average
• Specificity
• Measured heel, sole, and calf widths of foot (L0)
  and casts (Ln, n1,2,3,4)
• Avg. change (Ln/L0)-1 100

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Analytic Efforts Data/Results
Average Percent Change
Average loss of specificity over cast 2.13 Thus
any loss can be corrected with heat gun
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Analytic Efforts Observational Analysis

• Method
• Fabricated three AFOs with method to prove
  concept of procedure
• Observed fabrication procedure for hitches and
  quality of orthotics
• Results
• Angle of patients leg during casting can result
  in larger AFOs
• Casting socks can leave striations on inside of
  AFOs if these sections are not filled out
• Stocking material may stick to AFOs
• Changes
• More attention given to building out striations
• Casting angle more closely monitored
• Powder added to stocking to prevent sticking

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Further Analytic Efforts Mass and Durability of
AFO

• Mmass ?density Vvolume
• ?0.85 g/cm3
• V12x24x3/16
• 30.48 cm x 60.96cm x 0.47625 cm
• 884.9cm3
• M?V(1/3)
• (0.85 g/cm3) (884.90 cm3) (1/3)
• 250.72 g
• Durability must withstand 8-10psi

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Manufacturing Definitions Procedure

• 5 Steps
• Form STS Sock Mold
• Reinforce the Mold
• Apply Thermoplastic
• Remove Cast
• Finalize

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Step 1 Form STS Sock Mold

• Apply sock
• Wrap patients leg in plastic bag hold rubber
  tubing along anterior surface
• Soak sock material in water bath and stretch
  lightly for several seconds
• Roll on like ordinary stockings
• Smooth
• Pull tight by pulling on front
• Avoid bunching

http//www.stssox.com/foot_mold_construction.asp
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Step 1 Form STS Sock Mold

• B. Remove sock
• Wait until hard
• Periodically knock on cast to determine hardness
  a thump signifies its set
• Cut along anterior surface from the tibia to the
  ankle, then pull off patient

http//www.stssox.com/foot_mold_construction.asp
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Step 2 Reinforce the Mold

• A. Smooth rough spots and excess resin on outside
  surface using sandpaper
• B. Staple front flaps shut and secure using duct
  tape
• C. Fill cast to heel with sand, pound tightly
  into forefoot and toes

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Step 2 Reinforce the Mold

• D. Wrap stocking around one end of steel tube 10
  taller than cast (diameter 1 in.) and secure
  with electrical tape
• Cut off excess stocking
• Place wrapped end of tube into center of cast
• Fill cast up to 2 from top with sand, and pack
  tightly

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Step 2 Reinforce the Mold

• E. Pour thick plaster over sand to create a cap
  to seal in sand during vacuum forming
• F. Apply a 1/6 layer of modeling clay to bony
  prominences and possible pressure points
• Ankle, metatarsals, tibial head, any abnormal
  growths

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Step 3 Apply Thermoplastic

• Heat thermoplastic in oven _at_ 204C until clear
  and pliable (5 minutes)
• Wrap mold with 2 layers of detergent-coated
  stockings and secure tube onto vacuum pump using
  a vice
• Drape thermoplastic over mold
• Apply pressure (8-10psi) through vacuum tube
• Smooth thermoplastic around mold
• Pull excess towards anterior and cut off
• Let sit 5 minutes place in cool water to
  decrease cooling time (optional)

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Step 4 Cast Removal

• Trace boundaries on dried cast using bright
  marker
• Midway between anterior and posterior surfaces
• Over ankles, slightly inferior and anterior to
  metatarsals
• B. Cut along trace marks
• Dispose of excess thermoplastic
• Sand is reusable

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Step 5 Finalization

• Smooth edges using sander and grinder

• B. Add hinges or straps around tibial head and
  ankle

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Material Definitions

• Total cost 162 / 10 AFOs
• Sand 1-time or 0-time cost
• All other materials already present in lab

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Conclusions Problem Solved?

• Shorten duration of start-to-finish fabrication
• Originally 3-4 hours at intense pace now 1.5
  hours at comfortable pace
• Reduce required materials (plaster)
• Materials lost plaster (disposable), acetone
  resin, fiberglass sock
• Materials gainedSTS sock/plastic bag
  (disposable), sand (reusable), clay
• Low-tech easy laboratory implementation
• Sand, plaster, duct tape already present in lab
• STS Sock packages take up little space
• Uses machinery from current method
• Inexpensive
• approximately 48.30 in materials and labor
  prior methods cost on average 120/1 AFO

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Conclusions Problem Solved?

• Disposable patient-contact materials
• Plastic bagcheap, harmless
• Maintain patient physical and psychological
  comfort
• No different from current method
• Minimal training required
• STS Sock application and removal nearly identical
  to fiberglass application removal
• Requires no technical skills that are different
  from the current method
• AFO quality current methods
• Similar dimensions

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Conclusions

• All requirements met
• SUCCESS!

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Conclusions What Next? Further Casting Material
Analysis

• Are STS Socks the best negative casting material?
• Low-temperature thermoplastics may require less
  reinforcement prior to thermoforming fiberglass
  is currently used and may be a viable option
• Optimize and Standardize
• Thermoplastic thickness
• Vacuum pressure
• Oven temperature

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Conclusions What Next? Quality Testing and
Validation

• Clinical experiment to validate AFOs made with
  new method
• Double blind study
• Patients will wear an AFO made with either the
  new or old method for a month and rate the AFO
  based on comfort and durability
• Practitioners will rate AFOs based on quality
• Large patient population at least 50 subjects

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Lessons Learned

• Monetary cost for company isnt necessarily the
  dominant concern
• Practitioner habit
• Job loss?
• Space considerations
• Keep an eye out for existing technology
• Wanting to use vacuum sleeves was a little
  ambitious
• Nearly all materials used already available in lab

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What to do differently

• Entire faculty at our mentors lab was extremely
  helpful
• Should have utilized their knowledge more from
  the beginning
• Plan ahead and expect setbacks during
  implementation
• Serrated breadknives are not an ideal
  troubleshooting solution

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Look what I learned in BME 401!
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Questions?