Voxel-based morphometry (VBM) is a method of assessing brain gray matter volume that has previously been applied to various chronic pain conditions. From this previous work, it appears that chronic pain is associated with altered brain morphology. The present study was undertaken to assess these potential alterations in patients with painful hip osteoarthritis (OA).
We studied 16 patients with unilateral right-sided hip pain, before and 9 months after hip arthroplasty. This enabled comparison of gray matter volume in patients with chronic musculoskeletal pain versus healthy controls, as well as identification of any changes in volume following alleviation of pain (after surgery). Assessment involved self-completion questionnaires to assess pain, function, and psychosocial variables, and magnetic resonance imaging scanning of the brain for VBM analysis.
Significant differences in brain gray matter volume between healthy controls and patients with painful hip arthritis were seen. Specifically, areas of the thalamus in patients with chronic OA pain exhibited decreased gray matter volume. Furthermore, when these preoperative changes were compared with the brain morphology of the patients 9 months after surgery, the areas of reduced thalamic gray matter volume were found to have "reversed" to levels seen in healthy controls.
Our findings confirm that gray matter volume decreases within the left thalamus in the presence of chronic pain and disability in patients with hip OA. The results also show that these thalamic volume changes reverse after hip arthroplasty and are associated with decreased pain and increased function. These findings have potential implications with regard to optimizing the timing of orthopedic interventions such as arthroplasty.