Does the back of the knee look as if it has been flattened: The joint will be much wider and not as rounded as the other knee? Do you have any way to post a photo of the goslings legs? This would be very helpful.
If the knee looks flat, you may be looking at a slipped tendon. Depending on when this happened it may be able to be moved back in place and splinted. However, if it has been more than a couple of days odds are that it has shortened and the leg is semi-useless. This will sometimes cause the foot to look folded up as well. If the leg is not kept splinted for several days even if the tendon cannot be moved, then the tendon will continue to shorten and draw the leg up underneath the gosling.
If this is going on the gosling will mostly hop around on one leg, or scamper using the knee/hock joint instead.
If this is recent, you'll be able to see if it is the tendon by feeling on the inside and outside of the knee joint. The tendon is slightly round and moves. If you can feel it and it moves then gently try to push the tendon to the center of the knee. You will then need to use a Q-Tip broken in half taped to the leg (not too tight, but tight enough to not allow the tendon to move) on either side of the tendon. Keep a close eye on the leg and foot to make sure the tape is not too tight.
If it is too tight the ankle and foot will swell up. A very slight swelling is okay, but if it looks puffy that is bad (cutting off circulation) and it needs to be redone a bit looser around the leg.
As to the avian vet: If you have a college around that has a veterinary program, they may have an avian vet on staff that will be able to help you.
