The size of the femoral component can be estimated pre-operatively from the height and gender of the patient (Table 7.1). During the operation, based in part on the size of the femoral condyle and tibial component, the size may be adjusted. Pre-operative X-ray templating is less and less used.
Table 7.1 A guide to the size of femoral component based on information about height and gender and the size of the tibial component.
|
Women |
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|
Height |
Femur |
Matching tibia |
|
<60″ <153 cm |
X-Small |
AA, A or B |
|
61–65″ 153–165 cm |
Small |
A, B or C |
|
66–69″ 165–175 cm |
Medium |
C or D |
|
>69″ >175 cm |
Large |
E |
|
Men |
||
|
Height |
Femur |
Matching tibia |
|
<63″ <160 cm |
Small |
A, B or C |
|
63–67″ 160–170 cm |
Medium |
C or D |
|
67–73″ 170–185 cm |
Large |
E, F |
|
> 73″ >185 cm |
X-Large |
F |
A medium-size femoral component is appropriate for most patients. (It was, in fact, the only size used in the Phase 1 and 2 implants.) However, in small women, it is better to employ the small size and, in large men, the large size. The extra-large and extra-small sizes are rarely used in Western populations. In Asia the extra-small is used frequently. If there is doubt between small/medium, or large/medium, it is usually safer to use the medium. Similarly, if there is doubt between the extra-small and the small, or between the extra-large and the large, use the small or the large. The size is confirmed by the tibial size: Tibia A & B = usually small femur, Tibia C & D = usually medium femur, Tibia E & F = usually large femur. It is important to remember that all femoral and tibial sizes are fully interchangeable.