Transcript Oral Presentation#2

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
Current Socket Designs
Designed on a case-by-case basis for individual patients
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
stresses 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 in which forces are optimally
distributed throughout the residual limb-socket
interface
• Increase overall patient comfort
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
Placement of FSRs
• Impractical to cover every area of the residual
limb with sensors
• One FSR used in each area of clinical interest
(i.e. areas expected to face larger pressures and
cause patient discomfort)
• Patellar Tendon
• Medial Tibia
• Lateral Tibia
• Popliteal Depression
• Anterodistal Area
Data Acquision
Circuit design: current to voltage converter
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Circuit Design
Peak force expected to be around 4000 g ∴ feedback
resistor selected to be around 500 Ω to avoid saturation of
op-amp
Current Status
• Compact RIO (analog-to-digital converter)
connection with computer set up
• FSRs connected to measuring circuit
• 1/21/2011 – First trial at The Surgical Clinic with
Cody, a transtibial amputee patient
▫ Test if circuit reaches saturation
▫ Check sensor sensitivity – changes in resistance
that are too rapid with changes in force
undesirable
Design/Safety Considerations
• Wire thickness
▫ Thin enough to prevent interference with force data
▫ Thick enough to remain durable during movement
• FSR-wire connection
▫ Cannot break during movement
Future Work
• Successful first trial  construct more systems for
more patients (~10)
▫ Rotate FSRs within socket to cover entire area
▫ Test multiple surfaces (incline, flat, stairs)
• Analyze results, determine regions containing peak
forces
• Use different types of sockets on Cody
• Design and develop new socket: provide more
cushioning in areas of greatest force
Determination of Success
• Design is patient-driven
• Measure forces before and after fitting of new
socket and compare values
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.