Bowleggedness Correction Brace

University of PittsburghSenior Design – BioE 1160/1161

Amy MacevoyDaniel Steed

Lauren WolbertSarah Wyszomierski

April 18, 2006

Mentor: Morey S. Moreland, M.D.Children’s Hospital, UPMC

Background

• Redesign of pediatric bowleggedness correction brace

• Focus:• Correction and Support for

• Blount’s disease (tibia vara)• Bowleggedness (genu varum)• Rickets

• Children 2-13 years old• Specifically, 6.5 – 10.5 yrs

Background

• In U.S., ~ 277,000 children have severe bowleggedness (Frost & Sullivan)

• Improper growth in femur and tibial growth plates

• Rickets occurs most often in malnourished children

• eg.) In Mongolia, 32.1% of children under 5 (UNICEF)

• disorder, usually in children, involving softening and weakening of the bones

• caused by lack of vitamin D, calcium, or phosphate

Problem Statement

• Current devices are expensive, non-adjustable, custom-molded• Outgrowth: rapid, frequent

• Too expensive for low income households (up to $3,500)

• Also applicable in 3rd world countries

• Project goal: • Redesign pediatric bowleggedness

correction brace• Applies forces to correct angle of tibia and

femur growth plates• Adjustable• Affordable• Lightweight/Non-bulky

Design Requirements

• Material• Inexpensive• Easy to acquire• Durable

• Design• Simple to machine and assemble

• Plans to orthotists, companies• Parts easily acquired and replaced• Correction

• 3 point system• Corrective force at knee• Counteracting forces for stability

Design Requirements, cont’d

• Design, cont’d

• Adjustable• Interchangeable b/w

R and L leg

• Length

• Circumference

• S/M/L braces• Medium (5th –

95th percentile, 6.5 – 10.5 yrs)

• Lightweight• < 2.3 kg (5 lbs)

• Affordable• < $300 per brace

• Comfort• Reduce occurrence of

pressure sores

Economic Considerations

Significantly lower price• Up to $3,500 vs. ~ $250-300

• Not custom molded

• Adjustable

Market size• ~$83 million market

LSGH (Frost & Sullivan Reports)

Distribution• Medical supply companies

• Private Orthotists and Rehabilitation Specialists

Initial Design Considerations

•Design Problems:•Lack of:

• Support and correction at knee• Straps to secure

• Foot interface• Wanted sturdier design• Nested tubing

• Too heavy• Difficult to acquire correct dimensions

Version 1.0 Version 1.1

Initial Design, cont’d Proposed Solution

• Too many adjustment holes

• Difficult to machine

Version 2.0 Version 2.1

• Correction:• 3 pt system (shown in gold)

• Easily machined, common materials:• Aluminum 6061 Alloy

• Side holes

• Velcro/Neoprene straps• Grommets, elastic

• Machine screws/washers/bolts• Lock washers

• Optional padding• Washable

• Water clog• Breathable• Waterproof• Inexpensive

Design Solution

Prototype Fabrication

Milled/Drilled Beams

Insert strap grommets for adjustability

Insert padding

FINAL PRODUCT

Drilled Shoes

Trim bolts

Experimental Methods Used to Test Device Performance

• Human Subject Testing• Comfort• Usability• Strap Corrective Pressure

• Materials Testing• COSMOSWorks testing

• Deformation• Factor of Safety

Experimental Methods- Human Subject Testing

• 1 Human Subject Volunteer• Male, 9 yrs 9 mos• Height: 54” (60th percentile)• Weight: 70.5 lbs (50th percentile)

• Subject fitted with brace• Insertion of Pressurex-Micro pressure transducer film to record corrective pressure values• Standing for 10 minutes• Walking for 2 minutes

• Comfort• Subject answered survey questions, based on a scale of

1 to 5:• How uncomfortable are you feeling?

(5 = most discomfort)• How much do you feel the brace is slipping as you walk?

(5 = most slipping)• Do you feel that the heaviness of the brace is keeping you

from moving normally? (5 = most hindering)

• Overall, how comfortable do you feel in the brace? (5 = most comfortable)

** “No discomfort” does not imply “comfort”

• Usability • Gait alterations• Slipping of straps

Experimental Methods- Human Subject Testing

• Pressure Transducer Film Readings• Analyzed using Matlab program

• Converts scanned film .jpg to grayscale• Uses reference image and scaling factor to interpret grayscale values as pressure values within input range• Determined:

• Average maximum pressure (highest 10% of values)• Average overall pressure

Experimental Methods- Human Subject Testing

Comfort & Usability Results• COMFORT: Subject answered survey questions, based on a scale of 1 to 5:

• Discomfort = 2• Slipping = 1 • Heaviness = 1• Comfort = 3

• USABILITY: • Altered gait pattern

• Walked with slight limp• No slipping of straps

Pressure Results

Pressure in Corrective Straps (psi)Strap Mean MaxCalf 10.60 17.92Knee 13.53 19.84Thigh 11.15 19.69

Calf

Knee

Thigh

Highest concentration of max values occurred approx. at points of varus/valgus pressures

Discussion – Human Subject Testing

Comfort• Overall, minimal discomfort, slipping, and hindrance due to heaviness• Sources of Error:

• Subject pool size• Use of able-bodied child

• Unaccustomed to brace usage• Responses from children may be skewed

Usability• Limp severity may be due to uneven foot height• No slipping

• Allows for normal activity

Discussion – Human Subject Testing

Pressure• Mean pressure < Literature skin breakdown values

• ~ 15 – 35 psi• Highest values at knee (as compared to calf and thigh)

• Angle corrected• Targeted location of max pressure concentrations• Sources of error:

• Subject pool size, no specified conditions• Film handling• Reference to grayscale

• Uses:• Fitting• Correction progress

Experimental Methods – Materials Testing

• COSMOSWorks Testing• Each beam fixed on ends at bolt placement• Pressure applied at corrective force strap interface

• ~ Average pressure• ~ 20 psi (max pressure)

• Analyzed for• Deformation• Factor of Safety

Materials Testing Results

Pressure Deformation Factor of Safety

Average 0.000 811 in 8.1

Maximum 0.001 548 in 4.7

COSMOSWorks Results

Discussion – Materials Testing

• Small values for deformation• Determined to be insignificant • Will not affect integrity of brace

• High factors of safety• Desirable FOS values are those that are > 1 • FOS > 1 represents how much the stress is

within the allowable limit• Value > 1 for average pressures• Value > 1 for maximum pressures

Competitive Analysis

Custom-Molded HKAFO (Hip-Knee-Ankle-Foot Orthosis) • DeLaTorre O & P

• ~$1,400

KAFO, Metal (Knee-Ankle Foot Orthosis) • DeLaTorre O & P

• $795

Competitive Analysis

Strengths • Affordability• Adjustability

• Modularity• Pieces may be

replaced and moved without full brace replacement

Weaknesses• Not custom molded

• May hinder comfort, exact fit

Aluminum 6061 beam

$12

Neoprene/ Velcro Straps

$109

Nuts/Bolts/ Washers

$6.50

Shoe $3.50

Padding $13

Pressure film $13.67/patient

Manufacturing $31

Grommets $9

TOTAL COST $197.67

Constraints limiting Phase I testing

Economic• Pressurex-Micro transducer film reader ~$4000

Resources/Regulatory• Human Subject Testing

• Need more subjects, with specified conditions• Long-term testing to assess correctiveness• Gait testing with motion capture

• Lower body kinematics

• Materials Testing• Repetitive motion testing for durability

FDA Regulation

TITLE 21--FOOD AND DRUGS

CHAPTER I—FOOD AND DRUG ADMINISTRATION DEPARTMENT OF HEALTH AND HUMAN SERVICES

PART 890-Physical Medicine Devices

• Subpart D--Physical Medicine Prosthetic Devices • Sec. 890.3475 Limb orthosis • (a) Identification. limb orthosis (brace) is a device intended for

medical purposes that is worn on the upper or lower extremities to support, to correct, or to prevent deformities or to align body structures for functional improvement. Examples of limb orthoses include the following: A whole limb and joint brace, a hand splint, an elastic stocking, a knee cage, and a corrective shoe.

• (b) Classification. Class I (general controls).

US Food and Drug Administration: http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm

• Pre-existing Devices and Patents

• Majority: custom molded

• wide variety of devices, as well as device components, already existing

• some with patents

Regulation

Quality System Considerations

Manufacturability• Simple Design

• Common components

• Easy assembly

Human factors• Anthropometry

• Collected data for children to determine proper sizes (used 5th-95th percentile data for medium size)

• Shoe interface• Breathable• Waterproof• Soft material (contours

to individual)• Optional padding

• Washable• Straps

• Adjustable• Comfortable fit

• January• Improved sketches• Ordered materials

• February• Finalized sketch• Ordered pressure sensors• Practiced testing (using pressure sensors)• Completed market analysis

• March• Finished acquiring materials• Fabrication

• April• Finished design/fabrication improvements• Completed testing• Finalized documentation

Schedule

Group Task Breakdown

• Amy• Market and Competitive

Analysis• Background/Statistics• Clinical Correspondence

• Dan• Design• Market Research• Materials/Fabrication

• Human Subject Recruitment & Testing

• Mentor Correspondence

• Lauren• Initial Design• COSMOSWorks testing• Human Factors Analysis

• Sarah• Final Design & Anthropometry• Materials/Fabrication• Human Subject Testing &

Analysis• Clinical Correspondence

Future

• Design Improvements• Improved locking knee joint• More cost-effective straps

• Neoprene sheets ~$30 : Reduce overall price by $80

• Improved shoe interface• Threaded inserts: reduce shearing in shoe sole

• Materials testing to find more optimal beam

material/fasteners• Improved system for reading pressure• Formulate instructions for fabrication and use

• Sent to companies, orthotists, 3rd world countries, etc.

Acknowledgements

• Morey S. Moreland, M.D.• Children’s Hospital of Pittsburgh, UPMC

• April J. Chambers• Human Movement and Balance Lab

• Gregory R. Frank• Augmented Human Performance Lab

• Kevin McNulty• McNulty Landscaping & Handyman Services

• Brian Wlahofsky• Human Subject Testing

• Beverley Welte• Life Sciences Greenhouse

• The generous gifts of:

• Dr. Hal Wrigley• Dr. Linda Baker