A study has found that chronic pain caused by hip osteoarthritis, or OA, can actually shrink a brain region responsible for processing sensory cues and regulating consciousness and sleep.

The good news is that the brain shrinkage appears to be reversed when hip pain is relieved, in this case, through joint replacement surgery.

“The shape of your brain is changed by having painful arthritis, but in the patients I studied, who got better, the brain changed back,” says study author Stephen E. Gwilym, MD, PhD, an orthopaedic clinical research fellow at the University of Oxford in England.

Dr. Gwilym and his team studied 16 patients with hip OA. Their brains were scanned four weeks before they underwent a hip replacement and nine months after the surgery.

The researchers also scanned the brains of 16 pain-free volunteers who were matched by height, weight, age and sex to the participants with hip OA pain.

Compared to the healthy participants, people with hip OA pain had significantly less gray matter in the thalamus, a brain region that processes sensory cues, including pain.

Nine months after surgery, participants’ pain scores were virtually cut in half, and anxiety and depression scores all reduced to normal levels.

There were also no significant differences in the size of these brain regions between the two groups, suggesting that their brains had returned to a more normal state after surgery.

“We knew before that patients with chronic pain had changes in the brain. What we did not know is they are reversible after surgery,” says Michael Alexiades, MD, an orthopaedic surgeon at Hospital for Special Surgery in New York City who was not involved in the research. “I think most people think most changes to the brain are irreversible and often for the worse, and here they are showing that’s not true. The brain really can adapt one-way or the other. It’s good to show that there are things we can do to make the brain revert back to a more normal state.”