Living with chronic pain always changes the way we use our bodies, and we tend to favor our stronger side. This way of using the body gradually builds an imbalance which in the long term causes more muscle pain, that is one of the reasons why balance training is especially important if you suffer from chronic pain.
This is an inflated balance trainer from Harbinger Fitness, but there are many other similar types that are great too. Doing exercises on a balance trainer requires you to maintain your center of gravity over a surface that is constantly changing. Just standing on it is challenging and builds plenty core muscles as your body moves and shifts into and out of balance.
Training the small muscles will help hold and build support for the larger muscles, and here you get the added benefit of a foot massage. Intuitively I notice that working on the small muscles also affects my nerve system in a positive way, reducing hypersensitivity and decreasing the perception of pain. Combined with some endorphin releasing high pulse training it is definetly a pain-management winner!