If 10 mm of PI is corrected, femur height changes by:

• A. 2 mm
• B. 4 mm
• C. 6 mm
• D. 8 mm

Answer: (B)

When you adjust pelvic orientation in the sagittal plane, the change you see in the femur height is only a portion of the correction because the pelvis–hip–spine system distributes the movement rather than transferring it all to the leg length. A common teaching point is that about 40% of the pelvic correction shows up as a change in femur height. Therefore, 10 mm of PI correction yields roughly a 4 mm change in femur height. This is why four millimeters is the best, most consistent estimate.