I think it is the American Bred German Shepard that has a tendency to get hip dysplacia (where the thigh bone doesn't fit well into the hip socket, which is usually too shallow for the "ball" of the thigh bone, and becomes progressively worse with age).
A lot of large breed dogs can develop this.
I had a German Shepard that had hip dysplacia and it was heart wrenching to watch as she aged. We finally had to put her down when her quality of life just became too poor.
They do a surgery where they cut the 'ball' off the end of the bone. Over a few months, the muscle strengthens to a degree where they get around quite well on it, sometimes even when both hips are done.
If you do decide to go with a German Shepard... I'd make sure to do your homework and go with a reputable breeder and try to get some sort of guarantee against HD.