This was my first thought, but I'm skeptical this ends up being as bad a problem as you imply. You don't just pass an exam and then immediately get sent to an operating theater and given a scalpel. You do a medical internship and residency, and are supervised by experienced doctors. (Yes, I know, this is the US system, but I'd hope the systems in other countries would be similar, or at least provide similar protections.) I would expect a cheater like this might not perform well enough to ever make it into an operating room. And even if they did, it would only be in an assistant role, where they would likely show their incompetence pretty quickly.

Sure, the system overall isn't perfect, but detecting incompetence on the job (before being allowed to do any damage) is IMO the most likely scenario for cheating medical students who don't get caught at school.

Even if we consider other disciplines... say, civil engineering. You don't get your degree and then immediately get the job of Principal Engineer on a bridge-building project. You're supervised by engineers with more experience, and your work is checked and signed off on if it's correct. If your work consistently fails those checks, you'll get fired.