Yeah I'm a bit bemused too... Because if it was just his poorly ankle giving him grief then he would stand on his other leg wouldn't he? But he just sort of tips over like in the video. I read that the motor nerves for pigeon's legs run through/past their kidneys. So if there is any abdominal inflammation the pigeon can lose the use of its legs. But he doesn't feel swollen in the body, there are no masses in his tummy area I can feel.
Did yours just tip over frontwards/sideways when trying to stand? I keep finding this one resting on his chest/face with his bum in the air and his legs stretched out behind him.