Experts have been arguing for years over whether or not spinal manipulation eases lower back pain or is a waste of time and money. It turns out, they're all right.

Spinal manipulation is the application of force to joints to treat pain. It's most often used by chiropractors and physical therapists.

A study at the University of Alberta found that it does in truth relieve lower back pain for some patients, but not all.

The results point to the fact that lower back pain is complex, and treatments have to be geared to an individual patient's needs.

"Back pain, just like cancer, is a collection of different kinds of problems," says lead author Greg Kawchuk.

"We haven't been very good at distinguishing who has which problem, so we throw a treatment at people and naively expect that treatment to fix everyone's back pain.

"This study shows that, just like some people respond differently to a specific medication, there are different groups of people who respond differently to spinal manipulation," says Kawchuk.

Individuals with lower back pain underwent two sessions of spinal manipulation during the span of one week.

They reported their pain levels before and after treatment, and researchers used ultrasound, MRI, and other diagnostic techniques to measure changes in their backs, including muscle activity and spinal stiffness.

A control group underwent similar clinical examinations but did not receive spinal manipulation. A third group comprised of people who did not have lower back pain symptoms were also evaluated.

Participants who responded to spinal manipulation rapidly reported less pain and showed improvement in back muscle thickness, disc diffusion, and spinal stiffness.

The changes were great enough to exceed or equal the measures in the control groups, and the positive changes continued for the week of treatment.

On the contrary, researchers also found that people with back pain who reported no improvement also showed no physical changes either — the treatments simply had no effect.

Kawchuk said the study results don't support either side of the spinal manipulation controversy, but do help explain why there is so much disagreement over its effectiveness.

"Clearly there are some people with a specific type of back pain who are responding to this treatment, and there are some people with another type of back pain who do not," he said.

"Spinal manipulation acts so rapidly in responders that it could be used as a screening tool to help get the right treatment to the right patient at the right time."

The study was published in the journal Spine.