Modeling and fabrication of prosthetic sockets using selective laser sintering

by 1974- Faustimi, Mario Carneiro

In a patellar-tendon bearing (PTB) prosthesis, the inner profile of the socket is modified with respect to that of the residual limb so that the load is sustained in specific pressure resistant tissues, while relieving this contact pressure in other sensitive sites. Still, it is not uncommon for many patients to feel discomfort and pain in certain regions. Further pressure relief can be achieved through the incorporation of compliant features within the socket, which became possible with the development of rapid prototyping techniques for the fabrication of prosthetic sockets. In order to adequately design such features, an investigation of the magnitude of contact pressures at sites where relief is needed must be performed. This paper describes the acquisition of interface pressure data at the fibula head and the distal tibia during a walking test and during a step up/step down test, using thin-film tactile pressure sensors. The average maximum pressures obtained at the fibula head and distal tibia were 120 kPa and 75 kPa, respectively, for the walking test. For the step up/down test, the values for the peak pressures at these sites were 125 kPa and 90 kPa, respectively. Both results were considered consistent throughout the trials, with deviations of 2.3% for the walking test and 6% for the step up/down test. 1. INTRODUCTION 7 The socket of a patellar-tendon bearing (PTB) prosthesis is designed to reproduce the overall shape of the patient’s stump, but undergoes typical local modifications (rectifications) to cause most of the load distribution to occur in specific areas (e.g. the patellar tendon and the gastrocnemius muscle belly) that have a greater tolerance for load and pressure [4]. However, some sensitive areas may still be affected by enough contact pressure to cause discomfort to the patient. In addition, integrating larger local rectifications to relieve pressure may deteriorate residual limb/socket fit and compromise structural integrity. The introduction of local compliant features may provide an alternative solution to relieving concentrated high pressure areas. Although in conventional hand cast sockets such features are hard to implement, the production of sockets using freeform fabrication methods (to be discussed in Chapter 3) provides to the prosthetist with a fabrication technique to easily incorporate complex compliant topologies in the socket with no production cost penalty. To properly design such features, it is necessary to quantify the magnitude of the pressure in such sensitive areas during common workload conditions (to be addressed in