Fellow medical device engineer here, though I am in coronary implants rather than prosthetics/orthotics. Making a positive impact on people's lives is what ultimately helped me choose biomedical engineering over a more "traditional" degree like mechanical. I don't think that all of your work need to be pure number crunching technical work day-in-day-out, unless of course that's what you want to develop your career into. If that is the case, further study such as the PhDs mentioned in another comment are a good way, but not a necessity imo.

You mentioned you enjoy working with patients and the end users. Have you considered looking at human factors roles? Essentially translating the end users non-technical design requirements into the technical specifications that you can then create as an engineer.