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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
▫ 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,
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
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
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 in which forces are optimally
distributed throughout the residual limb-socket
• Increase overall patient comfort
Forces Acting on the Limb
• Shear– resulting from
frictional forces
between skin and
▫ 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.
Circuit Design
Placement of FSRs
• Impractical to cover every area of the residual
limb with sensors
• One FSR used in each area of clinical interest, 9
Pressure Tolerant
•Patellar tendon
•Medial tibial flare
•Mid shaft of fibula
•Medial tibial shaft
Pressure Sensitive
•Distal end of tibia
•Distal end of fibula
•Fibular head
•Anteromedial tibia
•Hamstring tendons
Design/Safety Considerations
• Wire thickness
▫ Thin enough to prevent interference with force data
▫ Thick enough to remain durable during movement
• FSR-wire connection
▫ Must not break during testing
• Transportability
▫ Must move from treadmill to ramp area quickly
• Power Supply
Preliminary Trial at The Surgical Clinic
Recent Work
• Alterations based on the
preliminary test
▫ FSRs reinforced with
nonconductive epoxy
▫ Circuit rebuilt
▫ Transportable Encasement
• Prosthetic leg testing
• Voltage calibration
• Drift correction
Current Status
Preparing to test with Cody on Friday, Feb. 11th
Developing LabVIEW module to record data
Attempting to get in contact with Dr. Robinson
Calibrating Voltage – Force curve
Future Work
• Conduct trials with additional patients
▫ Test on multiple surfaces (incline, flat, stairs)
• Analyze results, determine regions containing peak forces
• Test several different types of sockets with Cody
• Design and develop new socket: provide more cushioning
in areas of greatest force
• Determine success from patient feedback and peak force
reduction in critical regions
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),
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.