On transfemoral prosthetic knee design for natural human knee motion

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.