Background: A transfemoral prosthetic knee is an artificial knee used by above-the-knee
amputees. There are two major categories of transfemoral prosthetic knee designs: pin joint-based and
polycentric designs. While pin joint-based knee designs only allow pure rotation of the knee, polycentric
knee designs allow a combination of rotational and translational knee motion which is exhibited in
natural knee motion.
Objective: This work presents both the recently-patented design process and the resulting design of a
polycentric transfemoral prosthetic knee that approximates natural spatial human knee motion during
flexion and extension.
Methods: The design process includes tibial motion acquisition, Revolute-Revolute-Spherical-Spherical
linkage (or RRSS) motion generation, RRSS linkage axode generation and circle fitting. The polycentric
transfemoral prosthetic knee design produced from this process includes a gear joint with a specific
spatial orientation to approximate natural spatial human knee motion.
Results: Using the design process, a polycentric transfemoral prosthetic knee was designed to replicate
a group of five tibial positions over 37.5° of knee flexion (the amount of knee flexion in a standard
human gait cycle) with a minimal structural error.
Conclusion: The circular gear-based knee design accurately replicated natural spatial knee motion over
the tibial position data given for a standard human gait cycle. The knee design method must be implemented
over a broader sampling of tibial position data to determine if a circular gear-based knee design
is consistently accurate.