Q. My dog is over 7 years old, arthritis on both knees and now appears a few lumps on his spinal cord. Please help me to figure out problem.
A. Dogs can get arthritis in their spine as well. It is quite common, in some breeds more that others, but can effect mobility. I would suspect is is something like this, unless it is a lump/tumor. I would have it checked out by your vet
Any dog that has arthritis should have a consult with their vet to discuss pain management.
I would also recommend getting him on a glucosamine supplement if he isn't already. You will need to wean him on to it over a week or so, up to the full dosage and feed with food to avoid tummy upset.