Hip abduction/adduction ROM: which option correctly identifies the moving arm?

• A. Midline of tibia
• B. Midline of pelvis
• C. Midline of femur
• D. Dorsal midline of foot

Answer: (C)

When measuring hip abduction/adduction, you want to track how the thigh moves relative to the pelvis. The moving arm should follow the thigh’s long axis, so aligning it with the midline of the femur gives the true angle at the hip joint as the leg moves away from or toward the midline. Using the midline of the tibia would reflect knee alignment, and the dorsal midline of the foot would reflect foot/ankle position, not hip motion. The midline of the pelvis can serve as a stable reference for the stationary arm, but it won’t capture the thigh’s movement. So the moving arm should be the midline of the femur.