The hip joint has several degrees of freedom, of course. The Implant Template should contain this information in the Mating Features. In the given 2D projections, the rotational freedom of the joint is expressed by one single rotation around the axis of projection intersecting with the printing space at the 2D coordinate of the Mating Feature. Therefore, a Degree Of Freedom Sequence Item added to either the stem, the cup, or both.
In planning, this information could be used to visualize the rotational capacities of the joint after implantation.
Note: Technically, the degree of freedom could also have been added to the cup or even (each with half the range of freedom) to both. But since we are used to see femurs rotation with respect to pelvises and not the other way around, it seemed natural to do it that way.
[pic] Figure ZZ.3-5 ROTATIONAL DEGREE OF FREEDOM