Biomechanics of the patella in total knee replacement

An anatomical shape for the trochlea of the femoral component is an advanta ge in total knee design because in many cases the natural patella is preser ved. The trochlea profile can be described as having a V-shape, with a wide angle and a circular base. In such cases the plastic patella should have t he same profile, resulting in a generally conical shape. One of the questio ns regarding this design is whether the natural or artificial patella tilts in the femoral trochlea, producing wear and deformation of the plastic. We analysed the forces between the trochlea and the patella for various Q-ang les and flexion angles. We found that the patella is fully stable and witho ut tilting at all flexion angles, for a Q-angle of 14 degrees or less. Q-an gles greater than this represent severe misalignment, and hence the cone-sh aped patella is considered to be stable design.