Insert the twin peg femoral trial component [44 or 50] and ensure it is fully seated by tapping home with the femoral impactor (Fig. 7.28).
Figure 7.28
Insert a trial meniscal bearing of the chosen thickness (Fig. 7.29).
Figure 7.29
With the bearing in place, manipulate the knee through a full range of motion to demonstrate the stability of the joint, the security of the bearing and the absence of impingement. The thickness of the bearing should be such as to restore the ligaments to their natural tension, so that, when the bearing inserter/extractor is applied and gently lifted, the front of the bearing lifts 2 to 3 mm. In addition when a valgus force is applied to the knee, the artificial joint surfaces should distract a millimetre or two. This test should be done with the knee in 20° of flexion. In full extension, the bearing will be firmly gripped because of the tight posterior capsule.
Remove the trial bearing with the bearing extractor [15] (Fig. 7.30).