I have an arthritic knee that, in addition to the pain, limits my range of motion so I was in a similar position as you when looking to find a fitter that would work with me and that had experience working with people with some physical issues. Ended up going with a fitting from Signature. I liked the fact that they paid a great deal of attention to flexibility and range of motion when doing the fit - but at the same time tailoring the fit to the type of riding I do (more race oriented then recreational). Making some changes really helped balance out my pedal stroke. This probably could be done without the computrainer and video analysis but it was nonetheless cool to see.

I haven't picked up my new bike yet so I ultimately won't know the full benefits of the fitting for a few weeks but I am hoping for the best.

I, too, had chronic knee (and hamstring) pain. Doctor? Or Signature? Tempted, but ever the skeptic, I tagged along to Signature and watched while a friend got fitted. I was impressed enough to give it a go. Also, given that I was certain my pain was biking-related, I thought it would yield more injury-specific information than a trip to a doctor. Just a couple of adjustments (raised seat; moved cleats) gave my hamstrings immediate relief. Knee pain subsided, but since I discovered that I pronate, I followed through with a visit to a Dr.they recommended (John F. Connors; himself an athlete),and am now awaiting orthotics specially made for my biking shoes. Good luck to both of us!