I found the following very helpful, educational, and enlightening in regards to DOs (long, but worth the read if you've never heard about this):
The Paradox Of Osteopathy
In the spring of 1864, Andrew Taylor Still, a rural Kansas practitioner, watched helplessly as the best medications then available failed to save his three children from spinal meningitis. Bitterly disappointed, Still set out to devise an alternative healing practice. He eventually based his new system on the idea that manipulation of the spine could improve blood flow and thus improve health by allowing the body to heal itself. His philosophy included a healthy dose of moralism; patients were forbidden to consume any liquor and, as part of the break from existing practices, were also forbidden to take any medicine. Still founded a school to teach his new system of osteopathy in Kirksville, Missouri, in 1892.
Osteopathy was not the only system of spinal manipulation to be created in the late 19th century. Chiropractic, established in 1895 by Daniel David Palmer, aimed to relieve obstruction in the nerves rather than in the blood vessels. Osteopathy and chiropractic initially shared several characteristics. Both were founded when Americans freely chose from many systems of healing. Both were homegrown American systems created at about the same time by messianic Midwesterners. Both systems were seen by many Midwesterners as preferable to the reductionist European model of laboratory-based medicine, which was established most firmly on the eastern seaboard and was fast becoming the standard.
Over the course of the 20th century, medicine as practiced by M.D.'s (sometimes called allopathy) has come to dominate U.S. health care. Chiropractic and osteopathy, initially parts of a pluralistic medical system, have taken very different paths. Chiropractors have generally remained focused on spinal manipulation for a limited set of conditions, particularly those that are often resistant to allopathic therapy, such as back pain. Osteopaths, on the other hand, have worked hard to employ the entire therapeutic armamentarium of the modern physician, and in so doing they have moved closer to allopathy. )
The move toward assimilation became explicit in California in the early 1960s, when the California Medical Association and the California Osteopathic Association merged in what has been called the osteopathic profession's darkest hour. By attending a short seminar and paying $65, a doctor of osteopathy (D.O.) could obtain an M.D. degree; 86 percent of the D.O.'s in the state (out of a total of about 2000) chose to do so. The College of Osteopathic Physicians and Surgeons became the University of California College of Medicine, Irvine. Many osteopaths feared that the California merger was the wave of the future and that the profession would not survive. But it did, and in so doing it may have become even stronger. D.O.'s are now licensed in all 50 states to prescribe drugs, deliver babies, and perform surgery -- in short, to do anything that M.D.'s can do. Despite national recognition, osteopathy is still a regional phenomenon in ways that mirror its historical origin. The ratio of D.O.'s to the population varies by a factor of almost 3, from a low of 7.7 per 100,000 population in the West to a high of 20.4 per 100,000 in the Midwest; the number is 8.5 per 100,000 in the South and 18.3 per 100,000 in the Northeast. M.D.'s are far more evenly distributed throughout the country.
Osteopathy was originally created as a radical alternative to what was seen as a failing medical system. Its success at moving into the mainstream may have come at a cost -- the loss of identity. Most people -- including physicians -- know very little about the field (most people know more about chiropractic). Many people -- even osteopaths -- question what osteopathy has to offer that is distinctive.
Those who claim that osteopathy remains a unique system usually base their argument on two tenets. One is the holistic or patient-centered approach, with a focus on preventive care that they say characterizes osteopathy. That claim to uniqueness is hard to defend in the light of the increasing interest paid to this approach within general internal medicine and other areas of allopathic medicine. The other, potentially more robust, claim to uniqueness is the use of osteopathic manipulation as part of the overall therapeutic approach. In osteopathic manipulation, the bones, muscles, and tendons are manipulated to promote blood flow through tissues and thus enhance the body's own healing powers. The technique, based on the idea of a myofascial continuity that links every part of the body with every other part, involves the "skillful and dexterous use of the hands" to treat what was once called the osteopathic lesion but is now referred to as somatic dysfunction. Osteopathic manipulation is not well known (or practiced) by allopathic physicians, but for decades it has stood as the core therapeutic method of osteopathic medicine.
Joel D. Howell, M.D., Ph.D. University of Michigan Ann Arbor, MI 48109-0604
The rest of Howell's essay can be found at:
http://www.mercola.com/1999/archive/paradox_of_osteopathy.htm
It seems that many DOs do not really believe or practice osteopathy, but I am biased as many of the DOs I work with are surgeons. Although, I knew a bunch of DO internists, and they didn't really buy into it either - they just wanted to practice medicine. They seemed good at it.
Also, it seems if manipulation really significantly helped people, that could be shown in a randomized clinical trial. I have not actually researched for any trials, though. Anybody know some data?
