Progression of PTA related to the point of screw insertion. The point of screw insertion was judged by whether it was medial or lateral to the intertrochanteric line on anteroposterior and lateral radiographs. There was a statistically significant difference between the medial and the lateral point of screw insertion. Boxplots display the median, the upper and lower quartiles. Whisker lines from box plots indicate the percentile 10% and 90%. (Mann–Whitney U test, p = 0.001).