I agree: technically-- i.e., considering the manipulative side-- OMM and chiropractic are in the end pretty much the same. They both involve identification of putatively 'out of line' joints and bones and other areas of 'dysfunction' in the body, then using your hands to try to 'correct' the restriction/subluxation/somatic dysfunction. The OMM practitioners have their own terminology to decribe diagnosis and treatment, but the things they end up doing to the patient are similar, and in many cases will overlap with therapeutic techniques employed by physical therapists and occupational therapists. In my own primary care clinical experience, I would say that unless they are OMM specialists, most DO's employ a fairly narrow range of manipulation techniques, certainly less than ten.
Some DO's claim to use manipulation to treat non-musculoskeletal conditions such as hypertension, angina, etc., but there's very little evidence that they do anything beyond placebo-type effects in these cases. The same can be said for many chiropractic practitioners as well.
Education for DO's is very similar is identical to MD's, at least insofar as the non-OMM part of the world is concerned (e.g., many MD and DO students and residents take the same board exams), but chiropractic school doesn't have nearly so much overlap.
Finally, MD's and DO's are licensed to prescribe drugs, write hospital orders, and do other 'doctor' things that (at least in most states at present) chiropractors are not allowed to do.
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