Do not panic.
Runner ducks are prone to foot, ankle and leg injury or inflammation. If it seems to be inflamed and bumblefoot is NOT to blame, nor is there a thorn or other sharp object stuck inside, then all you can really do is take it to a vet. As this is very stressful for the duck, it is best to call the vet first to see if it is really necessary. In our case, the vet was used to dealing with all manner of poultry so was happy to accept our description of the problem with a few photos of the injury. She agreed that transporting the duck to a waiting room full of dogs and other animals would cause it a tremendous amount of suffering which was in this case unnecessary.
What can a vet do?
Assuming the vet does not find anything you missed, all you or the vet can do is give the duck anti-inflammatories.
How do you give medication to a duck?
It depends on the type of medication, of course, though our vet gave us a non-soluble gel in pre-dosed syringes. She said we should catch the duck and inject the liquid down its throat (also very stressful for the duck). Instead, I soaked the liquid onto food and fed it to the duck. I looked up this particular anti-inflammatory online and it is frequently prescribed to be eaten with food, so no problem there. You will need to devise a system of separating the ducks while they eat so that only the sick duck gets the medication - we only have two ducks, so I just held out two bowls and made sure the injured duck got the bowl with the medication. Feed it first thing in the day when it is hungry, and do not give it any other food until it has eaten the medicated food. If it takes more than one sitting for it to eat the food, this is no problem.
How long does it take to work?
The vet, based on the Indian Runner ducks she keeps herself, estimated a day and a half. Our duck, at her worst, had a really very severe limp indeed. Although we saw the slightest signs of recovery after 24 hours, the duck took almost a week to fully recover.
Can I eat the eggs after medicating my duck?
It entirely depends on the medication. If you are worming your ducks or giving it anything which is essentially a kind of poison, it would be unwise to eat the eggs. In our case, the anti-inflammatory prescribed was the same as one available over-the-counter/without prescription for humans, but in an absolutely miniscule dose. Even if 100% of the dose we gave it everyday had gone into the egg (it doesn’t, nothing like), the amount per egg would have done nothing to a human body. So, was I going to throw away the eggs from both ducks (they lay together and the eggs are identical, so we can’t tell the ‘medicated’ from the unmedicated) for 21 days after the end of the treatment, as some would recommend? 5 days treatment + 21 days waiting time X 2 eggs per day = 52 eggs thrown in the bin. No, of course not. I ate them. They were great. They were normal eggs in every way. One can assume that the cholesterol from those 52 eggs has done me far more harm than homeopathic amounts of mild anti-inflammatory which may have been in the eggs (but probably weren’t). That said, do not take human medical advice from someone writing a duck blog!
What if I can’t get to a vet?
I paid a total of €5 (a little over $5 US) for the consultation, a five-day course of medication and the syringes. There are guides online for dosing your duck with standard ibuprofen; this seems popular in the US where vet bills are high. If you can get to a vet and afford a vet, go to the vet.