Christine Bronikowski , Amanda Chen, Jared Mulford , Amy Ostrowski

1. Analyzing the forces within unilateral transtibialprosthetic sockets and design of an improved force minimizing socket Christine Bronikowski, Amanda Chen, Jared Mulford, Amy Ostrowski Advisor: Aaron Fitzsimmons, The Surgical Clinic

2. 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

3. Current Process for Constructing a Transtibial Socket • Transtibial Patient Evaluation a. Limb measurements b. Skin type and integrity c. Range of motion d. Hand dexterity e. Fine and gross motor skills • Cognition • Gel Liner Interface Material Selection • Most common: Urethane, thermoplastic elastomer, silicone • Fit Gel Liner to Patient

4. Current Process for Constructing a Transtibial Socket (cont.) • Cast and measure over gel liner • Modify negative model • Computer modeling • Hand modification • Fabricate positive check socket • Fit positive check socket – static and dynamic assessments • Fit final laminated socket

5. Current Socket Designs Designed on a case-by-case basis for individual patients

6. 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

7. 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

8. Forces Acting on the Limb • Shear– resulting from frictional forces between skin and socket • Can be minimized using socket liners • Perpendicular

9. 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

10. 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)

11. Data Acquision Circuit design: current to voltage converter

12. Circuit Design Peak force expected to be around 4000 g feedback resistor selected to be around 500 Ω to avoid saturation of op-amp

13. 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

14. 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

15. 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

16. Determination of Success • Design is patient-driven • Measure forces before and after fitting of new socket and compare values

17. References