Some water therapy would also be a good idea to strengthen the legs- but dont let it swim few more then 2 minutes or so while so little and that it has a warm place to go to straight after so it doesnt get chilled.
The fact that it can bend the leg is a hopeful sign at this stage. And happy to...
Poor little guy...
Have you tries to carefully see if he can move or bend his leg?? Have you had a good look to see if it seems fused??
Only thing I can suggest at this stage is to try to treat him like he had splay legs. As long as it doesnt seem to cause him any pain you could try...