Transcript Oral#4 - Research

Analyzing the forces within
unilateral transtibial
prosthetic sockets and design
of an improved force
minimizing socket
Christine Bronikowski, Amanda Chen, Jared
Mulford, Amy Ostrowski
Advisor: Aaron Fitzsimmons, The Surgical Clinic
Problem Statement
• Lack of research in the socket interface between the
artificial limb and the residual limb, specifically force
profiles
▫ Majority of research based on models with historically
proven success and qualitative assessments
Current Process for Constructing a
Transtibial Socket
1. Transtibial Patient Evaluation
a. Limb measurements
b. Skin type and integrity
c. Range of motion
d. Hand dexterity
e. Fine and gross motor skills
f. Cognition
2. Gel Liner Interface Material Selection
a. Most common: Urethane, thermoplastic elastomer,
silicone
3. Fit Gel Liner to Patient
Current Process for Constructing a
Transtibial Socket (cont.)
4. Cast and measure over gel liner
5. Modify negative model
a. Computer modeling
b. Hand modification
6. Fabricate positive check socket
7. Fit positive check socket – static and dynamic
assessments
8. Fit final laminated socket
Problems with Current Models
▫ Skin abrasion
▫ Pain or discomfort
▫ Tissue breakdown at the skin surface and within
deep tissues
▫ Pressure ulcerations and resultant infections at the
socket interface
Many of these problems arise from
forces at prosthetic interfaces
Project Goals
• Acquire accurate measurements of perpendicular
forces acting on the residual limb of transtibial
amputee during various movements
• Pinpoint regions with highest forces
• Design a socket system (combination of foot, liner,
and socket) in which forces are optimally distributed
throughout the residual limb-socket interface
Forces Acting on the Limb
• Shear– resulting from
frictional forces
between skin and
socket
▫ Can be minimized
using socket liners
• Perpendicular
Method of Force Analysis
• Force Sensing Resistor (FSR) placed between liner and socket
• Very thin– will not cause variation in force determination
• Decrease in resistance with increasing force, which leads to
increasing output voltage
Circuit Design
Circuit design: current to voltage converter
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Design/Safety Considerations
• Wire thickness
▫ Thin enough to prevent interference with force data
▫ Thick enough to remain durable during movement
• FSR-wire connection: 2 types of epoxy used
▫ Needs to withstand dynamic forces within socket
▫ Must be safe to place in contact with skin
• Power Supply
• ± 12V limited to 5V by voltage regulator
Placement of FSRs
• Impractical to cover every area of the residual
limb with sensors
• Used one FSR in each area of clinical interest
Pressure Tolerant
•(1) Tibialis Anterior
•(2) Distal End of Limb
•(3) Medial Tibial Flare
•(4)Mid Patella Tendon
•(5) Gastrocnemius
Pressure Sensitive
•(6) Fibula Head
•(7) Distal Tibia
•(8) Tibial Tubercle
Testing Combinations
• 3 Sockets\Liners
• Urethane (Otto Bock)
• Silicone (Evolution)
• Thermoplastic Elastomer (Ohio Willow Wood)
• 3 Feet Each
• Flex-Foot & Multi-axial Ankle
• SACH
• Vertical Shank ESF
• Several Conditions
•
•
•
•
•
Liner Only
Standing on Normal Limb Only
Standing on Both Limbs
Standing on Prosthetic Limb Only
Walking 2mph
Recent Work
• Created new LabView program to record data
• Calibrated each FSR
• Created Excel template to convert voltage
readings into pressure data
• Tested 9 combinations of feet and liners
LabView Program
FSR Calibration
Excel Template File
Current Status
Analyzing
Results
With Our
Advisor…
Future Work
• Analyze results, determine regions containing peak forces
• Based on results, test several new sockets with Cody
• Make specific regions of each trial socket more flexible or
rigid as needed to optimally distribute forces
• Design and develop final socket: provide more cushioning
in areas of greatest force
• Determine success from patient feedback and peak force
reduction in critical regions
References
Engsberg, J.R., Springer, M.J.N., and J.A. Harder. (1992). Quantif ying interface
pressures in below-knee-amputee sockets. J Assoc Child Prosthet Orthot Clin 27(3),
81-88.
Houston, V. L., Mason, C.P., LaBlanc, K.P., Beattie, A.C., Garbarini, M.A., and E.J.
Lorenze. Prelim ary results with the DVA-Tekscan BK prosthetics socket: residual
lim b stress measurement system. In: Proceedings fo the 20t h Annual Meeting
American Academy of Orthotist and Prosthetist, Nashvill e TN. P 8-9
Jendrzejczyk, D. J. (1985). Flexible Socket Systems. Cli n. Prosthet. Orthot. 9 (4), 27-31.
Lee, W.C., and M. Zhang. Using computational simulation to aid in the prediction of
socket fit: a prelimi nary study. Med Eng Phys. 2007 Oct;29(8):92 3-9.
Polli ack, A.A., Sieh, R.C., Craig, D.D., Landsberger, S., Mcneil , D.R., and E. Ayyappa.
Scientifi c vali dation of two commercial pressure sensor systems for prosthetic socket
fit. Prosthetics and Orthotics International, 2000, 24, 63-73.
Sanders, J.E., Daly, C.H., and E.M. Burgess (1993). Cli nical measurement of normal
shear stresses on a transtibial stump: Characteristics of wave-form shapes during
walking. Prosthet Orthot Int 17, 38-48.