Analyzing the forces within - PowerPoint Presentation

Slide1

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 ClinicSlide2

Problem StatementLack of research in the socket interface between the artificial limb and the residual limb, specifically force profilesMajority of research based on models with historically proven success and qualitative assessmentsSlide3

Current Process for Constructing a Transtibial SocketTranstibial Patient Evaluationa. Limb measurementsb. Skin type and integrity

c. Range of motiond. Hand dexteritye. Fine and gross motor skillsCognitionGel Liner Interface Material SelectionMost common: Urethane, thermoplastic elastomer, silicone

Fit Gel Liner to PatientSlide4

Current Process for Constructing a Transtibial Socket (cont.)Cast and measure over gel linerModify negative modelComputer modelingHand modification

Fabricate positive check socketFit positive check socket – static and dynamic assessmentsFit final laminated socketSlide5

Current Socket DesignsDesigned on a case-by-case basis for individual patientsSlide6

Problems with Current ModelsSkin abrasionPain or discomfortTissue breakdown at the skin surface and within deep tissues

Pressure ulcerations and resultant infections at the socket interfaceMany of these problems arise from stresses at prosthetic interfacesSlide7

Project GoalsAcquire accurate measurements of perpendicular forces acting on the residual limb of transtibial amputee during various movements

Pinpoint regions with highest forcesDesign a socket system in

which

forces

are optimally distributed throughout the

residual limb-socket interface

Increase overall patient comfortSlide8

Forces Acting on the LimbShear– resulting from frictional forces between skin and socketCan be minimized using socket linersPerpendicularSlide9

Method of Force AnalysisForce Sensing Resistor (FSR) placed between liner and socketVery thin– will not cause variation in force determinationDecrease in resistance with increasing force, which leads to increasing output voltageSlide10

Placement of FSRsImpractical to cover every area of the residual limb with sensorsOne FSR used in each area of clinical interest (i.e. areas expected to face larger pressures and cause patient discomfort)

Patellar TendonAnterodistal

Area

Medial Tibia

Lateral Tibia

Popliteal DepressionSlide11

Data AcquisionCircuit design: current to voltage converterSlide12

Circuit Design

Peak force expected to be around 4000 g

feedback resistor selected to be around 500

Ω

to avoid saturation of op-amp

 Slide13

Current StatusCompact RIO (analog-to-digital converter) connection with computer set upFSRs connected to measuring circuit1/21/2011 – First trial at The Surgical Clinic with Cody, a transtibial amputee patientTest if circuit reaches saturationCheck sensor sensitivity – changes in resistance that are too rapid with changes in force undesirableSlide14

Design/Safety ConsiderationsWire thicknessThin enough to prevent interference with force dataThick enough to remain durable during movement FSR-wire

connectionCannot break during movementSlide15

Future WorkSuccessful 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 forcesUse different types of sockets on Cody

Design and develop

new

socket: provide more

cushioning in

areas of greatest forceSlide16

Determination of SuccessDesign is patient-drivenMeasure forces before and after fitting of new socket and compare valuesSlide17

References