Optimizing Range of Motion
FIGURE 11 | Constant radius from 0° to 90° flexion
FIGURE 11A | Smaller closing radius
FIGURE 11B | Femoral position of ADVANCE® Medial-Pivot Knee
Inadequate range of motion has been cited as a cause for patient dissatisfaction and revision in TKA.10 Although preoperative range of motion has been shown to be a major factor affecting postoperative range of motion, the sagittal curvature of the femoral implant also has a significant effect on range of motion. Andriacchi et al found femoral implants with "boxy" curvatures limit range of motion.5 By designing the curvature of the femoral implant to closely match the anatomic femur, range of motion can be maximized.
The ADVANCE® femoral implant has a constant sagittal radius of curvature extending from full extension to 90 degrees flexion (Figure 11). The curvature values for each femoral implant were chosen from a detailed analysis of 130 cadaveric femora. In the study, the radius of curvature of the femur was measured between the average flexion-extension axis and the distal surface of the femur every 10 degrees to 90 degrees flexion.29 A smaller closing radius, which has been shown to increase range of motion, was also included as a design feature in the femoral implants (Figure 11A).36 To further increase range of motion, the shape of the femoral component is complemented by the anterior stability of the ADVANCE® Double-High and Medial-Pivot tibial inserts. Both components provide a robust anterior lip which maintains the femoral component in the posterior third of the articular surface (Figure 11B). This creates a long quadriceps lever arm and reduces anterior sliding in flexion. By doing this, flexion is increased due to a more effective mechanical advantage and avoidance of posterior tibio-femoral impingement.
