If you are not sure it is Arthritis, I 've had a condition called Trigger Thumb in both hands over the years , usually happens around this time of the year when there is a ton of yard work, wheelbarrows of garden soil, mulch, raking etc. I've had 2 cortisone shots in one and one in the other which alleviated the issue each time. Due to the catabolic effects of cortisone shots , 2 is all my specialist will do then surgery....
Arthritis in the hands is a challenge and can be debilitating, hoping for the best for you