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 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 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

Circuit Design Circuit design: current to voltage converter Vout=Vref*(-RG/RFSR)

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 total 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 NI LabVIEW / RIO

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

References