Researchers also showed that the cerebellum, the center for balance and the coordination center for walking, gets bigger in patients with chronic arthritis of the hip. But after the hip replacement it reverts back to normal size since it no longer has to work in overdrive.

“A key point is that while these patients got good pain relief, and their brain changes reversed, some patients don't get complete pain relief from hip surgery,” Dr. Gwilym says, adding that leads to the question – “do these people have brain changes which have gone 'too far'?”

Doctors say the study makes a very strong argument for getting pain under control, especially when the physical pain is associated with walking.

“This work forces the question as to the maximum time a patient should be left in pain prior to surgery if we know that these changes are ongoing,” Dr. Gwilym explains. “Some, less reversible, causes of pain are also known to be associated with similar changes and patients may hit a point where the changes are not reversible with surgery and remain in pain. This is speculation.”

Dr. Gwilym also says this study begs the question of whether or not these brain changes could affect other things too. “Certainly some of the areas which change in volume have been linked to areas that are responsible for mood and cognition. So in theory, yes, the pain may lead to changes in mood for neuroanatomical reasons,” he explains. “We saw that patients scored lower on our assessments of depression after their pain was relieved by surgery and brain changes reversed.”

Dr. Alexiades says it’s great to have this detailed way of studying improvement post-surgery.

“It’s a fascinating study from a neurological point of view and confirms what we as orthopaedists have seen for years. We can have patients walking little or horribly and after replacements go back to normal function and normal walking, and this confirms structurally their brain is agreeing with it,” Dr. Alexiades says.

The study was published in Arthritis & Rheumatism.