The basic and key differences between what we do. It's more than just a matter of branding. It's a matter of philosophy within the continuum of care.
Disclosure: I have worked with chiropractors both in my office and in their offices. I have used one in the past for back and neck ailments, and to this day consult one from time to time. (After all, it's really not useful to "crack" oneself, and the vast majority of PTs don't manipulate).
This is a common question that I get form time to time and while there are some key points that need to be explained, the truth is that while there is overlap in some of what we do, there is only a very small percentage of PTs who use manipulation ("cracking" the neck, back or other joints) in their practice. My guess is less than 1%.
Manipulation (which is in our scope of practice) is a shared technique between osteopaths, chiropractors, and physical therapists. The philosophy of use is what differs.
What makes this more complex is that the chiropractic profession has fractioned within itself. I have been told by my chiropractic friends that there are at least three "factions" (for lack of a better term) within the chiropractic professions, each wanting its philosophy, ideas, and approaches to be the standard.
What you need to know is quite simple. Chiropractic manipulation was born out of the work of BJ Palmer in the 1800s. Palmer did archaic studies of the nervous system's response before and after manipulation. Palmer believed, as most chiropractic philosophy still holds, that subluxation (bones being fixated "out of place") of the spinal vertebrae causes gross tension or impingement on the nerves arising out of the spinal cord. This is known as "subluxation theory". Many chiropractors today are taught that it is this alterned nerve function which is the cause or precursor to disease.
In theory, it sounds reasonable. However, the problem exists in that it has not been uniformly proven within the scientfiic community. There have been little to no high-quality scientific studies which definitively prove the theory true. In fact, in 2012 the head of the British Chiropractic Society published a statement denouncing "subluxation theory".
Physical therapists, on the other hand, use manipulation after performing an evaluation to determine where a person's movement impairment is, and if there is some loss of mobility in a spinal segment that may be underlying it. Granted, some chiropractors do similar, but many still use x-rays to visualize the spine in an attempt to detect subluxation. They will all generally use their hands to palpate (feel with the hands) to determine where there is joint restriction.
With regard to technique, there are some differences with regard to the mechanics of the technique. PTs generally use a "momentum induced" technique derived from British Osteopaths, or a "translatoric" technique derived from Norwegian or Australian influence. It is usually a bit more gentle than general chiropractic, which uses an end range thrust (this can vary depending on their schooling).
This article could go on and on. But in my opinion the difference is really headed towards a matter of brand preference. A good, skilled PT will use manipulation as an adjunct to a comprehensive program of exercise training, self-management strategies/education of the patient, appropriate modalities, and other strategies. In my experience both can work, but I feel that what I do is more complete.
A PT professor at Quinnipiac University once told me the difference between a skilled PT and a chiropractor is that a skilled PT will teach the patient how to care for themself so they don't have to return for follow up care for several months. My experience is that that is fair generalization, however specialists emerge in any field.
Whatever you decide, know that every vocation, every profession, every field, every company has its leaders. At the end of the day, your goals need to be met and you need to feel better.