This seems to be a hot topic both here and on my other forum.
I have really really jacked up hips from hip displaysia. Usually this is caught at birth and people were put in a plavik harness to correct it. Or, it is a mild form of displaysia and it is caught later in life when things start being arthritic or range of motion is poor. Mine was not caught at birth. It was caught when I was two and was walking like you would imagine a person with legs not attached to their pelvis would walk.
After several reconstructions to try to build me an acetabulum and get stuff stuck together, and then 40 years of walking on it and having a kid, the area looks like a mess. The femoral head is very flat (looks like you took a normal one made out of play doh and squished it) and the 'acetabulum' if you can call it that is super shallow. Like barely a curve it is so shallow.
So, once they got in there they had to carve in another area to put the much much larger prosthetic acetabulum in. Not just a slight carve out to get it to fit like a normal hip replacement but if you look at the images they basically had to take out the equivalent amount of bone to the size of the implant. I had no 'cup' space. Adding to that, the top of my pelvis is completely deformed. While most people have those two round top portions to their pelvis, mine are pretty flat and completely skewed to the right.
All that is to say that once my doctor got in there and made everything new and aligned and functional, the last thing he wants to happen is for his nice work to get jostled before everything has had time to settle. He wants to ease into it. I have never had normal range of motion. I have never sat criss cross applesauce in my life. I have never been able to do a proper lunge, so now that I have a hip joint that will be able to do those things in the future, my body has zero experience with this. Heck, just having my leg be the same length now (he added 3/4 of an inch) is bonkers. So, that is why we are going slow.