Hi there. This certainly sounds like it could be arthritis. It is very common in geese as they age. It has two forms- septic and aseptic arthritis. In septic arthritis the foot is usually very swollen and sometimes misshapen, it often starts as bumblefoot- a bacterial infection of the feet, that can then spread into the joints. As you have looked at the foot and it looks normal, i suspect it is aseptic arthritis- or degenerative joint disease, to give it it's full name.
You can treat the pain caused by this to make the goose more comfortable, there is a drug you can obtain from the vet called 'Metacam' which is a non steroidal anti inflammatory drug, this is given once daily according to weight.
If you are organic, there are homeopathic remedies for arthritis in geese, 'Bryonia' extract is meant to be particularly good- take a look at www.woodlandnaturalremedies.com- their 'FARM 140' formula for arthritis contains bryonia and could be an option for treatment.
Andrea
Bird Veterinarian
15 years in companion animal practise, BVM&S degree Edinburgh university