The results of that study by Li and Bombardier (2001) show that 569 therapists were interviewed. Only 30 percent surveyed said they thought spinal manipulation was effective in treating low back pain. Studies showing manipulation is successful are fairly new. It may take a bit longer for therapists in Canada and some parts of the United States to see these reports.
What we know so far is that spinal manipulation improves symptoms and function in about two-thirds of the patients. There are a couple qualifiers to that statement. First, the patient must be having acute back pain. This means the spinal manipulation takes place within the first month of painful symptoms.
Second, the patient must have just back pain, not back pain that spreads to the buttock or down the leg. And third, motion in the low back area shouldn't be restricted but be within normal limits.