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The lines they draw on x-rays are a throwback to CDH/DDH. Those drawn lines which revealed loss in the upper anterior cup are very insensitive to cup damage on the backside . Often the only clue we get of considerable acetabular damage is that hip ball centering in the cup has drifted.

Good hips on x-ray. The neck shaft angle (green ) looks flat (“valgus”) in the inset view because the leg as seen is rotated. That is what angles do when viewed from an angle – they go flat by projection perspective. The red line (Shenton's) can only be off if the acetabular center and the femoral head center no longer coincide.