Roughen the femoral and tibial surfaces including the posterior condyles, by making multiple small drill holes with the cement key drill [38] (Fig. 7.31). Clean the bone surface with a pulse-lavage and dry.
Figure 7.31
When surgeons start using the Oxford prosthesis, we strongly recommend that the components are fixed with two separate mixes of cement, because this makes it easier to retrieve any cement extruded posteriorly.
The tibial component
Place a small amount of cement on the tibial bone surface and flatten to produce a thin (about 1 mm thick) layer covering the whole surface. Insert the component and press down, first posteriorly and then anteriorly, to squeeze out excess cement at the front. As there is evidence to suggest that early application of cement to implant aids fixation, an alternative approach is to spread a thin layer of cement on the undersurfaces of the tibial component in addition to the layer on the tibia. If this is done, an osteotome should be used to force the cement into the surface of the tibia and sweep the remaining cement off the tibial surface.
Use the right-angled tibial impactor (Fig. 7.27) with the toffee hammer, applied from posterior to anterior, to complete the insertion. Ensure there is no soft tissue under the component. Remove excess cement with a Woodson cement curette [11] from the margins of the component. Insert the femoral trial component and pressurise cement by flexing the knee to 45° and then inserting the appropriate thickness feeler gauge. With the feeler gauge inserted, hold the leg in 45° of flexion while the cement sets. Do not fully extend or flex the leg as this may rock the component and compromise the fixation.
Once the cement has set, remove the feeler gauge and trial femoral component and look carefully for, and remove, cement that may have extruded. Finally slide the flat plastic probe [13] along the tibial articular surface, feeling for cement at the edges and posteriorly.
The femoral component
From the second mix, force cement into both femoral drill holes and fill the concave surface of the femoral component with cement. Apply the loaded component to the condyle and impact with the impactor held at 45° to the long axis of the femur. Remove excess cement from the margins with a Woodson cement curette. Pressurise the cement by inserting the appropriate feeler gauge with the knee at 45° of flexion and holding the leg in this position. Do not fully extend or flex the knee as this may rock the components and may loosen them. Once the cement has set, remove the feeler gauge. Clear the medial and lateral margins of the femoral component of any extruded cement. The posterior margin cannot be seen directly but can sometimes be seen reflected on the tibial surface and can be palpated with a curved dissector.
Experienced surgeons may wish to cement both tibial and femoral components with one mix. This is acceptable provided they are comfortable that they can do this and leave minimal cement to be removed from the back of the knee. A cement with a long working time should be used. An assistant should apply cement to the components. After the tibial cement has been briefly compressed with the femoral trial and feeler gauge, these should be removed and then excessive cement removed from around the tibia. The femur should then be cemented. Final pressurisation is achieved with a gap gauge inserted with the knee at 45° flexion.
