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The implant is selected with the aid of the templates. The choice of implant is based on three key landmarks (Figs. 2 & 3):

• On the diaphysis, the axis of the implant drawn on the template must match the axis of the femur when the prosthesis is in a central position, neither in varus or valgus.
• The digital point (D) determines the height at which the implant should be placed. The shoulder of the prosthesis must be flush with the lower part of the digital fossa (d).
• The infero-lateral point or junction of the trochanter and the diaphysis (E): the lower and lateral part of the prosthesis should rest on the infero-lateral part of the greater trochanter (e) with at least 3mm of cancellous bone retained.

ABG II cup templates
Templates are available for the determination of the appropriate ABG™II cup size and position, and of the centre of rotation of the hip.

Points to check
The size selected must ensure the best metaphyseal fill whilst retaining as much of the calcar as possible (Fig. 4).

• Optimum metaphyseal fill: given a choice between two sizes, it is better to use the smaller size (thus preserving the most cancellous bone) but only if excellent, especially rotational, stability of the broach is achieved intra-operatively.
• The centre of the femoral head (T) on the template must be on a line drawn at right angles to the axis of the femur and, generally, passing through the tip of the greater trochanter. The various prosthetic head options (short, standard or long necks) allow the lower limb to be adjusted to precisely the right length.
• No proximal contact between the stem and the femoral cortex. If there is contact, the template indicates the minimum diameter to be reamed out during surgery.

Neck osteotomy line
The neck point (C) can then be identified on the template and the neck osteotomy line linking the digital point (D) to the neck point (C) can be drawn on the X-ray. This creates an angle of approximately 60° with the diaphyseal axis. The vertical osteotomy line is parallel to the axis of the femoral diaphysis and runs from the digital fossa towards the apex of the greater trochanter.

The pre-operative template should be regarded as an indication of the definitive implant size which will be selected during the surgical procedure. A careful check on the stability of the broach and head trials enables the final implant size to be determined.

In some cases (depending in particular on the approach used), the femoral stem templates can be used for the following measurements which can be useful during surgery:

• Osteotomy site: having identified the most prominent part of the lesser trochanter (st), the exact distance between the osteotomy site and the lesser trochanter (C-st distance) or between the apex of the femoral head and the osteotomy can be measured by means of the graduation on the template.
• Implant position: in order to avoid valgus or varus positioning, it is often helpful to measure the precise distance between the medial edge of the implant and the lateral cortex of the calcar and to use the resulting measurement during surgery.

Fig. 3 ABG ll HA Stem template for stem size 6	Fig. 4 X-ray with template showing osteotomy landmarks.

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