Why does forced adduction/internal rotation of the hip feel so uncomfortable with hip dysplasia?

Hip Dysplasia: Developmental hip dysplasia causes the normal curve of the hip joint to be abnormal or flattened. This can effect the range of motion or the hip. Also degenerative hip arthritis is associated and occurs prematurely in some. A common early symptom or significant oa of the hip is pain with internal rotation and adduction. Also associated may be changes within the labrum of the hip.

Not all dysplasia : Usually dysplasia caused by fai, femeroacetabular impingement, causes those symptoms. It causes pain by the femur and pelvis inappropriately bumping into each other.