[Design of an external prosthetic system with a polycentric mechanism]

This medical and engineering work explains the process carried out to build a four-barred polycentric knee mechanism using a mechanical actuator for modular prosthetics. Imitation of the knee performance was the main goal, as well as to cover the basic needs of amputated patients with a low production cost.

The polycentric knee mechanism was developed in three stages. The first one was the design and building of the four-barred mechanism using materials as stainless steel 304 and aluminum 6,061 which both have high reliability, corrosion resistance and a relatively easy modeling capability. The total mass was of 700 g. Autocad was used for design and effort analysis was done by using ANSYS. At the end of the first stage, it was observed that its density did not allow mass optimization and no assistant actuator was available for the walking movement. In the second stage, mechanism mass estimation was done by using Alumold 400; this material brings lower density than stainless steel keeping strength and fatigue resistance higher than aluminum 6061. The better ergonomic device was built; a mechanical actuator based on a spring was implemented and tested on two female patients, one geriatric and one 16 years old. The third stage will be described in a future publication, the device mass was optimized by using poly-tetra-fluor-ethylene enhanced with carbon and carbon fiber. Also, the mechanical actuator was complemented with reo-magnetic liquid addition and an electronic control.

At the end of this research, an external polycentric knee mechanism was developed, by observing movement stages, velocities, ergonomics, shapes, sizes and significant weights of Mexican patients. Effort analysis by finite element was done and it was determined that the mechanism was capable of modifying its center of rotation according to the knee flexion angle making it a polycentric mechanisms. Also, it was tested on two patients, both females, one 16 and one 75 years old.