Swollen Toe

[Emily.g]

Hi everyone, my rat Stevie is around a year and half years old and ever since I’ve had him he’s had a swollen middle toe. It has never bothered him and has never grown until recently. In the last few weeks it’s gotten bigger and I’m not sure if I can do anything about it. It still does not bother him but I was wondering if anyone knowns what it is? Ive attached a few photos.

Thanks!