We have little experience of loosening of cementless components as it seems to occur much less frequently than with cemented components. We are not aware of any cases of late femoral loosening but have heard of cases in which the femoral component was observed to be loose at the end of the operation and a cemented component was therefore implanted. These presumably occurred because the 6 mm hole was accidently enlarged during the operation. Care must be taken to avoid toggling instruments that go into the 6 mm hole.
We have not seen late tibial loosening but are aware of a number of cases in which the tibia has subsided early (Liddle et al, 2013). Typically, during the first month, the post-operative course and radiograph is normal. However, during the next few months, the patient complains of new or persistent pain and the radiograph demonstrates the tibial component has developed a complete radiolucency, has subsided into valgus and tipped posteriorly. If this is treated conservatively, the pain tends to settle spontaneously, the implant stops subsiding and the radiolucency eventually disappears as the component becomes securely fixed (Fig. 11.10).
Figure 11.10 Early valgus subsidence and pain. Subsequently the pain settles and the tibial component becomes securely fixed.
Factors that may contribute to tibial subsidence are an undersized component that does not reach the posterior cortex, a deep resection, multiple and deep vertical cuts or damage to the back of the keel slot. Perhaps the most important factor is that the bearing may be jammed against the wall in flexion. If this occurs, there will be a large load on the lateral side of the tibial component causing it to tip into valgus. Once tipped, the bearing will move medially and normal load distribution will be restored so integration can occur.
As the symptoms tend to settle and the components integrate, it is recommended that these cases should be treated conservatively. Patients should be reassured and advised to restrict weight bearing.
