A good case to highlight that while the line of Klein is a helpful line when assessing the pediatric hip, like any line or measurement, it is only a help.

On the frontal radiograph, the right femoral epiphysis is clearly not normal. The apparent loss of height does not represent real loss of femoral head height, but the posterior displacement of the slipped epiphysis.

In cases like this, the line of Klein does not help with the diagnosis.

A monkey could make the diagnosis on the lateral view!