1. Cardiology: you can "fast-track" or do what's called a CI (clinical investigator track) through residency and do only 2 instead of the traditional 3 yr residency. The board allows you to do this (in certain acredited programs) and still sit for the medicine boards if you continue onto a fellowship. To be board certified in cardiology, you need to do a 3yr fellowship. Typically medicine fellowships require 1 year full time clinical duties with 2 years of research and/or clinical duties. Interventional and electrophys require an additional year. 6yr minimum post graduate work, usually more.
2. There are some orthopods that are MD-PhD's. Not a ton. The AAOS is making a push to get more clinician-scientists into ortho. The rush has not been far from overwhelming though. Currently, most academic departments have NO MD-PhDs on staff. By the time you are looking for jobs (> 14 years from now if you're currently premed), things should be different. Very few ortho residency programs now offer an opportunity to get an MS or PhD in any kind of integrated fashion but that may also change. In conclusion, things are not arms-wide-open inviting and some/many md-phd programs will discourage you to do this but don't be discouraged because there are folks out there.
3. PhDs are NOT offered in clinical departments. With the exception of the rare integrated clinical department, the PhD portion of MD-PhD or res-PhD is performed under the aegis of a basic science department or a interdepartmental graduate program. 2 years for a PhD in surgical residency can be done but is extremely rare. 3-4 years is more typical. The trend for g surg right now is to get rid of the 2 yrs mandatory research or to make it optional even in some academic programs.
4. Why do a MD-PhD and go into a surgical specialty. You are needed and will be very wanted. Many (but not all) ent, ortho, uro, obgyn programs are already trying to recruit more of those interested in research. Neurosurg and ophtho have been successfully doing so for some time now but can certainly use a continued steady flow. And res + fellowship is typically 6-7yrs (longer for g surg, n surg, depends for uro).
5. Send me a PM if you want to discuss more.
MD-PhD 2003, U Penn, Matching in Ortho