Picture quality

• The extended ventro-dorsal view is familiar though not always easy to position. Persevere, as well positioned pictures are easier to interpret.
• The femurs are parallel, the obturator formaninae are symmetrical and the sacro-iliac joints are a matching pair confirming that this is a well positioned picture.
• Exposure factors are equally important - over exposure tends to obliterate detail while under exposure obscures, for example, visualisation of the dorsal acetabular rim through the femoral head.