Conditions Guinea pig's hind legs bend outward completely! Assistance needed!

Hi I got 2 male guinea pigs about 3-4 months ago. Both of them get along well as one is older (Fluffles) and the other is younger(Coco). Everything was going perfectly fine until a couple of days ago i noticed Coco didnt want to use his hind legs. He did everything else including eating and drinking yet he didnt want to walk. At one point when he released the cleaning fluid from his eyes, he attempted to clean himself yet he couldnt get his hands over his head so he just tried to shake off the fluid instead. I took him and put him in my tub filled with water about 1.5 inches high. I held him up yet still had him in the water to see if he would swim to see if he has movement in his legs. He attempted to swim and succeded yet stopped right away. so at this point i knew he wasnt paralyzed. I thought maybe he might have had a vitamin c definciency, so i got seperated him from Fluffles and gave him his own cage and hoped for the best. 2 days later I noticed something quite shocking. Coco's hind legs were bent outward completely! I had no idea how this couldve happened as im the only one with access to them! Please help i dont know what is wrong with my guinea pig!