I hand feed my frog beef heart frequently, and when I feed pellets (which is actually pretty rare) I actually have to pretty much drop 'em on her head and she just opens her mouth and swallows, lol. So I think your critter with the leg problem can be hand fed, too. I have noticed though, that even after I've hand fed her, she'll use her forelimbs to adjust the food in her mouth, like maybe if it's too big of a piece, or not quite situated right. So, feed small pieces, I guess.
My frog also tends to catch her own fish without using her forelimbs too much.
I tried to find more info about limb malformations/variations, aka either mineral deficiencies or thyroid issues. The problem is, I don't have any journal access anymore since I'm not in school. You might have better luck than me. It could be either of those, or just a fluke developmental variant (or something else entirely, really, those were just the things I thought of off the top of my head).