With the knee in about 45° flexion, make a hole into the intramedullary canal of the femur with the 4 mm drill [54]. It should aim for the ASIS. This should be completed with the 5 mm awl [33] (Fig. 7.14(a)).
Figure 7.14(a)
The hole must be situated 1 cm anterior to the anterior edge of the intercondylar notch and in line with its medial wall (Fig. 7.14(b)).
Figure 7.14(b)
Insert the intramedullary (IM) rod with the introducer until the introducer stops against the bone (Fig. 7.14(c)) [24, 29]. If the rod cannot easily be inserted do not hit it with a hammer as it may perforate the cortex. Instead enlarge the hole and perhaps move it further anterior.
Figure 7.14(c)
Flex the knee to 110°. This must be done with care, because the medial border of the patella abuts the IM rod. Using a marker or diathermy, draw a line down the centre of the medial femoral condyle.
Confirm the size of the femoral component based on the size of the tibial component (Table 7.1). Insert the femoral drill guide [41] for the appropriate size, set to the size of the G-clamp used, either 3 or 4 (Fig. 7.15(a)). (See Chapter 6 for advice on the adjustment of the drill guide.) If the correctly adjusted femoral drill guide cannot be inserted or feels tight, remove about 1 mm of cartilage off the posterior femur using a sharp chisel. There should be no need to re-cut the tibial plateau.
Figure 7.15(a)
Insert the IM link [26] into the IM rod and into the lateral hole of the femoral drill guide (Fig 7.15(b)).
Figure 7.15(b)
If necessary, tap it gently in with a hammer. The link ensures correct alignment of the guide. It will not necessarily position the guide in the correct medial/lateral position. This needs to be adjusted (Fig. 7.15(c)).
Figure 7.15(c)
The 6 mm hole must lie in the centre of the medial condyle, halfway between its medial and lateral borders. This is done by ensuring the medial and lateral bollards of the drill guide adjacent to the 6 mm hole on the guide are equidistant from the condyle edges. It can be confirmed by looking into the 6 mm hole and verifying that the line previously drawn down the centre of the condyle is in the centre of hole (Fig 7.15(c)). Ensure the cowl indicating the front of the component does not overhang medially. If it does, move the guide laterally.
Once the guide is centrally positioned, the 4 and 6 mm holes are drilled. The drill guide and link can then be removed.
