"The secretary used to do it, but he left at the end of last season and because I have a bad back I've been doing it," the 29-year-old told BBC Sport.
"I tweet every chance, every goal, every yellow card, I do it constantly.
"There was a 90% chance I wasn't going to get on, but the centre-half got injured with 10 minutes left and we'd already used the other two subs."
The FA has offered to take up the slack by tweeting for Kenna so he can focus on his playing duties, something his manager will apparently appreciate.
Kenna said: "I'd better be careful because after Sunday's game, the manager fined me £10 for having my phone in the dugout."