To be fair, some of these costs would exist in any business. There are always capital equipment costs, employee costs, administration costs and in some cases research and development costs. However, you are on the right track with your criticism of artificially high medical device costs. Indeed, these high costs can be seen not just in prosthetic hands or limbs but also in more mundane devices such as hearing aids and prescription eyeglasses. In my estimation there are two main reasons for this:
First, the devices are sold through specialized middlemen who bill your insurance company which in turn bills you and perhaps your employer for premiums. This is the classic third party payer problem that exists throughout the healthcare industry here in the United States and is in no small part responsible for the high costs which are ultimately borne by the consumer in the form of higher premiums and higher out of pocket costs.
Second, and related to the first point, the market for FDA approved medical devices here in the United States is highly regulated and therefore high cost. There is a great deal of regulatory rigmarole and ceremony required to bring a product to market. This imposes costs of course, but it also results in delays while the product winds it's way through the circuitous approval processes. By the time something is approved for sale as a medical device it's not only expensive but often obsolete or at least several generations behind the state of the art technology.
Finally, it ought to be remembered that medical devices are now assessed an additional tax under Obamacare, on top of any previous expenses. It's hard to see how this will lower costs, especially for those who find themselves in need of a medical device. Although, I suppose that "reform" is in the eye, or the hand in this case, of the beholder.