The proper function of the OUKA depends upon the unimpeded freedom of the bearing to translate on the surfaces of the fixed components. The limits to its movement must be set by tension in the cruciate and collateral ligaments and in the posterior capsule, not by impingement against bone, retained osteophytes or fragments of cement.
The lateral projection may reveal retained posterior osteophytes on the femur or extruded cement at the back of the tibial component, either of which may impinge on the posterior edge of the bearing in flexion (Fig. 9.8).
Figure 9.8 The sites of possible impingement of the bearing are indicated.
Impingement anteriorly, due to inadequate removal of femoral bone from in front of the component, is the most frequent finding in retrieved bearings, but radiographs do not show this site well.
Impingement between an ‘anvil’ osteophyte just anterior to the ACL insertion on the tibia and osteophytes in the roof of the notch may occur and limit extension. Confirm that the anvil osteophyte is removed.
