Actually, one of the first complaints I had was that it hurt to play my cello. Stupid thing to tell the doctor, especially since there were other every day activities that were bothering me more - like pushing on those spring-loaded medicine cabinet doors, or writing with a pen. "Well, you must be playing too much." I knew that wasn't it - many, many people play hours a day and I was only maybe playing an hour a day.
But I also knew it wasn't supposed to hurt to play, and it never used to when I played multiple hours. I sought out a teacher to check my technique, to make sure I hadn't somewhere in my time off and coming back developed some unknown-to-me bad habits. Nope. But he had some great ideas for developing my technique further...
I learned that serious double stop work, double extensions, etc. only served to strain and aggravate my small (for a full sized cello) hands further.
My most painful joint now is the CMC - at the base of the thumb - the left thumb. Curious, as that thumb has such a small role in left hand cello work in the neck positions, where the bulk of my playing is. But the above mentioned strain and also some repetitive playing such as is common in a lot of orchestral playing causes an increase in tension in my hands which I suppose affects it.
The CMC joint seems to usually be one of the more commonly affected (by arthritis) joints, and I learned from the hand specialist (physiotherapist) that it is often the left one in right handed people, probably because it usually does the grunt work like holding the pot while the right hand washes, etc.
I am, however, now also developing pain in my right hand. BUMMER! The right thumb has a much bigger role in cello playing. So far I think it has only been once that it actually bothered me to the point of having to put the bow down, but my practice has been much curtailed this season in order to rest the left hand.
After reading about splints for musicians in Playing (Less) Hurt by Janet Horvath, I wondered if something on my left thumb would help me. I first tried something my husband already had: a wrist splint. But I modified the way I was wearing it to support the thumb. Definitely helped, but was too bulky for cello playing, really. I tried a few actual thumb splints before getting to the hand therapist, and none of them really worked for playing with, either. The hand physio guy made me this:
I have been able to wear it for some of my teaching time, but found this softer "Thumsling" which provides a more modest support for the joint, but doesn't get in the way of playing as much as the rigid plastic or the bulkier wrist splint.