Neck osteotomy, using a postero- lateral approach
The digital fossa can be identified and a line can be drawn on the neck at a 60° angle to the axis of the femoral diaphysis (Figs. 5 & 6).

The neck is resected in two cutting planes using the oscillating saw:

• the first plane follows the diagonal line of the posterior aspect of the neck - no anteversion is necessary.
• the second plane is vertical, parallel with the medial aspect of the greater trochanter and extends upwards from the digital fossa.

Fig. 5 Neck osteotomy

Fig. 6 Neck osteotomy line

Neck osteotomy, using an antero-lateral approach
Since the digital fossa cannot be seen, the only reliable landmark is the lesser trochanter. Consequently, the distance “C-st” (between the centre of the lesser trochanter, and the femoral neck resection level) determined on the preoperative template should be applied to the femur.

The neck is resected using an oscillating saw, at an angle of 60° to the axis of the femoral shaft. The cut is extended laterally to the junction of the femoral neck with the greater trochanter, care being taken to ensure that the saw does not violate the greater trochanter. When this cut has been completed, the vertical osteotomy is performed. Toothed bone forceps grip the femoral head and brief use of the chisel at the level of the digital fossa completes the osteotomy.

The femoral head and neck are then removed by releasing the capsule downwards and forwards on the neck. It should be kept in a cup filled with physiological saline (grafts may be required during the procedure).

Next, the acetabulum is exposed and prepared for the insertion of the acetabular component.