What Causes Pain In Neck,shoulder And Back After An Injury?

I slipped and fell on the ice at work in the parking lot, in 2010 had my left shoulder operated on, I grabbed the car door with my left shoulder, twisted my back, and hit my left knee, since the fall my neck gets stuck going to left, the neck, shoulder, back are extremely painful - the x ray taken by Doctor shows arthritis, but no fracture, she is sending me for therapy for three weeks and I have been off of work since the accident. Can the x rays not have shown any thing since the tear in my shoulder was bigger then the MRI and X ray showed in 2010 - what role does the Arthritis play as to the pain and trauma that I suffered from falling at work ? l