Thanks for the question! Without doing a thorough evaluation, we are unable to comment on your specific situation. We can offer some information that should be helpful.
First of all, it is important to know that there is significant variation in “normal” motion. What someone may consider to be “hypermobile” may be a normal for someone else. It is not uncommon for a dancer to have mobile hips or a pitcher to have a mobile shoulder. Since you play piano, it stands to reason that you may have joints in your hand that are fairly mobile.
It’s also important to note that having more mobile joints does not necessarily mean that you will have arthritis or a dislocation. Dislocations usually occur during an accident or some form of trauma and mobility is often an indication of good joint health and not indicative of arthritis.
That being said, if you start to notice your thumb is in pain while playing the piano, it may be worth seeing a certified hand therapist as they can determine if your joint mobility could be contributing to your pain. They also may be able to provide you with a custom splint to help reduce pain if that ever becomes an issue.
If you are interested in some exercises, activities that promote general strengthening about the thumb are a great way to promote stability. It many ways playing the piano is a great strengthening exercise. You may also find general dexterity and grip strength exercises similar to the ones in this document to be beneficial. For more information, reference the below blogs written by our Musician Rehabilitation Specialist, Hope Hampton.
Please note, this reply is for informational purposes only. It’s not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician, physical therapist, or other qualified health provider with a medical condition.