With good long term results achieved with the cemented Oxford arthroplasty, there seems little justification to develop a cementless device, particularly as cementless TKA have not performed as well as cemented TKA (Ranawat et al., 2012). There are however potential advantages. For example, many failures are caused by cementing errors, which often occur with inexperienced surgeons using the Minimally Invasive Surgical (MIS) approach. Furthermore, many of the failures in the Registers are reported as being from loosening. Some of these are likely to be true loosening but others may be the result of misinterpretation of the radiolucent lines that commonly are seen in association with a cemented tibial component. Both of these issues could potentially be addressed with cementless components.
The mechanical environment at the bone/implant interface is very different in TKA to UKA, with the forces in a TKA not being ideal for cementless fixation whereas those in UKA, particularly mobile bearing UKA, are. Despite cementless TKA not performing well (Ranawat et al., 2012), it is therefore well worth considering cementless mobile bearing UKA. Optimally there will be only compressive forces at the interface. With the mobile bearing OUKA, excluding the effects of friction, the forces are predominantly compressive.
With UKA, whether the load across the knee is central (Fig. 2.21(a)) or eccentric (Fig. 2.21(c)) there is always compressive load under the tibial component. However, following TKA, although central loading (Fig. 2.21(b)) causes compression, eccentric loading (Fig. 2.21(d)) may cause tilting and loosening of the tibia.
Anecdotal evidence that suggests that cementless components will work comes from an Italian surgeon who implanted Phase 2 Oxford components without cement. Despite having no fixation, these components functioned well. We were able to review some radiographs taken five years postoperatively. They were satisfactory, albeit with radiolucencies. This confirms that the loading on the components is predominantly compressive and that even without any formal fixation, the components function well. Therefore, with cementless fixation, one would expect a reliable result.
