The cementless implants are impacted into the bone, tibial component first. It is essential that a small toffee hammer is used for impaction – a heavy hammer can cause a fracture. The tibial implant is assembled into the introducer/impactor [16] by locating its lugs into the recesses on the underside of the implant and tightening the thumb wheel (Fig 7.32).
Figure 7.32
The component is then carefully impacted into the bone (Fig. 7.33).
Figure 7.33
The keel is carefully driven into the keel slot from the front. The knee is fully flexed so the upper surface of the impactor is parallel to the posterior femoral saw cut thus increasing the available space. The component is impacted at an angle to the tibial surface so its posterior edge slides along the tibial surface thus pushing soft tissue out of the way. When the front of the component has reached the position where the front of the template was, the component is impacted down.
Before the implant is fully seated, the introducer/impactor is removed by unscrewing the thumb wheel. Using a small dissector, any soft tissue interposed between the implant and bone is swept out. Small adjustments can be made to the AP position of the component by using the side of the handle of the plastic cement removal chisel or a punch. Final impaction of the tibial component is achieved with the standard tibial impactor, placed over the centre of the keel.
Often the tibial component does not seat down fully and may be 0.5 mm proud. This should be accepted as it will subside with time. Attempting to hit it hard with a heavy hammer may cause a fracture.
Impaction of the femoral component is achieved with the standard impactor (Fig 7.28), used in line with the main peg hole. It is essential that a light hammer is used for impaction – a heavy hammer can be a cause of fracture. Both components are examined to ensure they are fully seated.
