The legs should be exercised whenever you have time - several times a day, a sort of physio for them. Move the joint around, straightening it as much as possible, then reapply the splint, with padding at pressure points. Sometimes it does get better, sometimes it doesn't and the lamb needs to be destroyed - by stretching and flexing the leg frequently you will be able to judge if there is any appreciable improvement. For the hoof, would a tiny trim help?