Having demonstrated in Chapter 2 that a fully conforming mobile bearing can minimise polyethylene wear, in this chapter we show that a mobile bearing prosthesis, unconstrained in the sagittal plane, can restore natural mobility and stability.

For surgeon readers who are less interested in the theoretical background, it might be advisable to go straight to Chapter 4, Indications, or to start by reading the final section of this chapter, The Loaded Prosthetic Knee. If that proves interesting, the surgeon might attempt The Unloaded Prosthetic Knee. For the more research minded surgeon or engineer, it seems more logical to start with the Unloaded Natural Knee (the longest section of the chapter) and to read from there. The chapter may also be of interest to those surgeons embarking on the use of a bi-cruciate retaining total knee replacement.

The numerous writings on knee movement and the many methods used for its measurement and analysis over the past two centuries have been reviewed in detail by Pinskerova, Maquet and Freeman (2000) and by Freeman and Pinskerova (2005). We will not attempt to repeat such reviews. We present our own evidence as to how the passive soft tissues of the human knee interact to control the passive motion of the bones and how this motion is modified in activity in the presence of muscle force, external loads and consequent tissue deformation. This provides a base with which to compare the kinematics and mechanics of the Oxford Knee in cadaver specimens and in living patients. In designing these studies, we have used as our model the example of D’Arcy Thompson: