The short answer is:

Physical Therapy was prescribed because it is the firstline treatment for most chronic pain conditions. It is less expensive, non-invasive, and generally more successful in the short term than most other modes of therapy.

There are different types/kinds/specializations of PT just as there are for medicine, so getting the right kind of PT is of great importance.

http://en.wikipedia.org/wiki/Physical_therapy
http://en.wikipedia.org/wiki/Manual_therapy

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