Spindly Leg Sydrome?

[Whistly]

I would give it a couple of weeks if the frog appears to be struggling then yes put it down, BUT if it is still a fat happy frog then keep it alive check out Ebony's deformed Southern Bell frogs they are fat and happy and live good lives and their back legs don't work.

[Flick]

Well as you can see, he is quite fat. And he is a very active little hunter, he can be uncoordinated but he never misses a cricket!

[Whistly]

Then there's your answer.

[frogged]

Keep him alive if he's eating and healthy.