INFLUENCE OF PROSTHETIC DESIGN FOR THE FIXATION OF JOINT REPLACEMENT IN THE LOWER LIMB

Abstract

The aims of Total Knee Arthroplasty (TKA) are to relieve pain and to recreate joint function and stability. Knee joint stability is intimately associated with the concept of joint motion. A stable knee joint is one that maintains an appropriate minimum contact force between the articulating surfaces throughout the functional range of motion of the joint. Thus a TKA is stable when moving through its range of motion it can carry the required functional loads without pain, maintaining contact on non-peripheral located regions and produce joint contact force of normal intensity on the polyethylene insert. Any factors causing an abnormal joint contact force and/or abnormal eccentric position of joint contact force might lead to polyethylene and component loosening. The TKA stability and function are strictly related to the interplay among the implant component alignment, articular surface geometry (flat or congruent polyethylene insert), cruciate-retaining or cruciate-substituting prosthesis design, soft tissue balancing and muscle action. Tibial component loosening continues to be a common mode of failure following TKA. Tibial component fixation is critically dependent on an equilibrium between the mechanical loads and bone resistance to them. Even if it is difficult to find a strict correlation between locomotor lower limb function and knee kinematics, TKR kinematics and position of the point of contact between femur and tibial insert are fundamental biomechanical parameters to understand the reason of extensor mechanism deficit often found in TKA patients and the risk of polyethylene wear. In the present study we will present TKA kinematics and position of the point of contact between femur and tibial insert in fixed and mobile insert focusing in TKA design features. Different knee joint kinematic patterns has been found between fixed and mobile TKA design particularly when congruent artificial joint surface is coupled with mechanical constraint such as the spine-cam mechanism.