Apply the anti-impingement guide [45] to the condyle (Fig. 7.23(a)), and use the anterior mill assembly [28, 32, 42] to remove anterior bone and create clearance for the front of the bearing in full extension. Take great care to ensure the mill does not damage the tibia or patella. Before starting the mill, engage it on the peg and ensure the spring loaded mechanism moves freely. When milling, push firmly in the direction of the peg axis, taking care not to tilt the mill. Mill until the cutter will not advance further.
Figure 7.23(a)
Leave the anti-impingement guide in place and use the osteophyte chisel [49] to remove any posterior osteophytes (Fig. 7.23(b)). This should be done medially and laterally as well as centrally. Remove the guide and, using the osteophyte chisel, break off any attached osteophytes and sweep them down off the posterior capsule, and remove them. If possible palpate, with a little finger, the proximal part of the condyle to ensure all posterior osteophytes are removed.
Figure 7.23(b)
Insert the tibial template, the twin peg femoral trial component [44 or 50] and a trial bearing [48] of appropriate thickness (as determined when measuring flexion and extension gaps). With these components in place, manipulate the knee through a full range of motion to ensure there is no impingement of bone against the bearing in full extension and full flexion (Figs. 7.24(a) and (b)). If the bearing impinges in flexion, the knee will open up like a book. If this happens, the osteophyte chisel should be used again to ensure all posterior osteophytes are removed.
Figure 7.24(a)
Figure 7.24(b)
Ensure the bearing is not jammed against the vertical wall. If a narrow dissector put between the bearing and the wall is gripped by the bearing, consider redoing the vertical tibial cut 2 mm more laterally.
Remove the trial bearing and femoral trial component using the appropriate extractor [15] and slap hammer [9].
Note: Gap gauges are used to measure the gaps because they do not stretch the ligaments. The meniscal bearings have a 3 mm high posterior lip which, after multiple insertions, may stretch the ligaments.
