The common myth of tiny medical robots is just that - a myth. The gap between current public Nanotech such as stain resistant trousers and better tennis racquets seems unbridgeable. However even if the dream of nano-submarines is impractical then maybe the more mundane technologies will have applications; for example stain resistant trousers uses nano-materials which repel liquids - this could be used in medical tools to stop blood sticking to surgical tools.
Strengthened materials such as tennis racquets use carbon nanotubes mixed in with conventional materials to increase the strength, with such strong materials replacement bones would be much stronger than the original bones; clearly an improvement. This may not seem as unlikely as you may think. Advancements are already taking us there.
However it will be a long time before Nanotech finds its way into large-scale use in the public medicine sector. Many people are uncertain about the affects of Nanotech and it will largely depend on how newspapers paint Nanotech.