#18 I do not mind the image of this logo. It is unusual and sort of works, although I do not think everyone looking at it will understand it. It looks strong and supportive (outside curved bars) balancing the flexed spine. I am not sure what the green horizontal line in the logo means. Do not line the text color or font - prefer blacks and grey to provide that professional look (eg (as per #5 and #22). The tagline would need to be changed or deleted (the word Therapy appears twice.)
I like that you have incorporated the spine image into the back of one of the letters.... Perhaps to try this in the letter "B"? Another option would be to stack "New" and "Back" on top of each other, and then using the back of both the letters of N and B to create a spine image... Is this possible? What do you think? There might be a gradational change of colors from top to bottom to suggest a change or improvement of function.... just a thought.
Another idea is to use the curved side of the letter "B" to superimpose the spine onto, since, in a true spine there are two forward facing (the thoracic and sacral) and two backward facing (the cervical and lumbar) curves. The lumbar and cervical curves are the most important--the other two are partly (thoracic) or completely (sacral) fixed.