Enumeration of human knee prostheses--an overview

Very often clinicians prescribe a limited number or only one type of knee mechanism because it has been found reliable or perhaps specific information on the range and variety of all available mechanisms has not been on hand. The clinician rarely has the opportunity to see all the mechanisms in a common perspective to compare the relative merits of one mechanisms with another. An attempt has been made to enumerate the available human knee-prostheses, both implants and external prostheses, according to their motion. An historical development of knee prosthesis is discussed. A classification procedure is developed for both internal and external prostheses based on their primary functions. The two major classifications in either of these prostheses are monocentric and polycentric mechanisms. A mechanism whose center of rotation does not change through out the range of motion is considered as monocentric mechanism and a mechanism whose center of rotation changes during its operation is considered as polycentric mechanism. The implants are categorized as hinged and non-hinged knee joints. The external prostheses are further classified based on certain primary functions like control in swing phase and/or in stance phase and in extension. The hierarchical classification scheme will benefit kinematicians and designers to analyze the available mechanisms and make necessary improvements. This will also provide a ready-reference to the prosthetists in selecting the best-fit prosthesis from a large family of prostheses.