We know that arthritis can really be debilitating to humans, but what about pets? Pets can also suffer from arthritis. If you don’t treat pet arthritis, it can actually lead to a variety of other medical conditions. Most of the time, it is caused by a lack of joint fluid. Fluid helps to protect the bones, and keeps them from rubbing together. When this joint fluid starts to diminish in old age, the bones can rub together and cause trouble with the joints, and it can lead to severe pain.