A quick look at the numbers of surgeries performed annually in the US,  especially who the patients are—most notably their age—is enough to hint at why investors are more than a little overjoyed with their new-found wonder stocks: Intuitive Surgical and MAKO Surgical, both with skyrocketing share values with seemingly no end in sight.

There’s a world of growth in robot-assisted surgery ahead and investors are taking it for a ride. Overlooked by many is the fact that Intuitive has penetrated overseas sales very little while MAKO has zero penetration, which is all about to change in a hurry if robot-assisted surgery even loosely follows the U.S. model.