A new study into the neuroscience of clinical pain suggests that perceptions of stiffness may not reflect the actual state of the spine and joints. The team's findings may pave the way for new therapies that help those with chronic pain in their lower back.
Sometimes, people with lower back pain do not manage to get rid of the pain. In fact, it is estimated that for approximately 20 percent of those with the condition, the pain evolves into chronic pain - that is, pain that does not ease for 12 weeks or more.
But might the discomfort all be a matter of perception? Could feeling pain not necessarily reflect the state that our body is in? A new study published in the journal Scientific Reports suggests so.
The researchers were led by Dr. Tasha Stanton, who is a senior research fellow at the University of South Australia's School of Health Sciences in Adelaide.
Studying feelings of lower back pain
Dr. Stanton researches the neuroscience behind clinical pain, and her motivation for this new study stemmed from previous evidence that amputees feel pain in a limb that they no longer have, or that the subjective feeling of pain can be influenced by a range of other perceptual factors such as visual or auditory stimuli.
She and her team recruited 15 people with self-reported feelings and symptoms of chronic lower back pain, and an additional 15 healthy, age-matched control participants.
The team conducted three experiments. In the first one, they used an "established, customized device, validated in humans" that applies pressure to the spine and can objectively measure the resulting stiffness.
The researchers compared these measurements with what the participants reported to feel, using a scale from "not stiff at all" to "most stiff imaginable."
In the second experiment, the participants were told that they would receive an applied force and were then asked to estimate as accurately as they could the magnitude of the force they received.
Finally, the third experiment aimed to examine whether or not adding sounds to the perception of pressure would change how the stiffness is perceived.
Feelings of stiffness: 'A protective response'?
The researchers wanted to evaluate this last point based on the results from the first two experiments, which led them to the hypothesis that "feeling stiff may represent a protective perceptual construct."
"People with chronic back pain and stiffness overestimated how much force was being applied to their backs - they were more protective of their back. How much they overestimated this force related to how stiff their backs felt - the stiffer [it] felt, the more they overestimated force. This suggests that feelings of stiffness are a protective response, likely to avoid movement."
Dr. Tasha Stanton
"In theory," Dr. Stanton adds, "people who feel back stiffness should have a stiffer spine than those who do not. We found this was not the case in reality. Instead, we found that that the amount they protected their back was a better predictor of how stiff their back felt."
Dr. Stanton also explains the results of the third experiment, saying, "[We] found that these feelings could be modulated using different sounds. The feeling of stiffness was worse with creaky door sounds and less with gentle whooshing sounds."
"This raises the possibility that we can clinically target stiffness without focusing on the joint itself but using other senses," she says, believing that the findings open up new therapeutic avenues for chronic back pain.
"The brain uses information from numerous different sources including sound, touch, and vision, to create feelings such as stiffness," says Dr. Stanton.
"If we can manipulate those sources of information, we then potentially have the ability to manipulate feelings of stiffness. This opens the door for new treatment possibilities, which is incredibly exciting," she concludes.