Patient dissatisfaction after TKA has not been improved dramatically since the introduction of new alignment (navigation, custom guides) and balancing techniques. Orthopaedic surgeons consider the ligaments as essentially passive stabilizing structures. However, during the activities of daily living, the joints are stabilized primarily by our muscle actions that both move and stabilize the joints. Isometric motion of the joint does not cause the distance separating the bone attachments to change. The practical importance of isometry is confirmed by the fact that ligaments are elongated irreversibly if the strain exceeds a given level (5%). In ligament surgery as well as in TKA, the concept of isometry is highly important. In this paper we wish to highlight the fact that the role of the soft tissue envelope goes beyond structural and mechanical support. The presence of mechano- and nocireceptors in the structures around the human knee joint has long been reported but is underrecognised by TKA surgeons.