Arthritis is simply defined as an inflammation of any joint in the body. A joint is any bone that meets with another bone. Examples of joints are the elbow, hip, knee and even joints exist in the craneum (skull). Arthritis can occur in any joint. Causes can be due to: trauma, congenital, aging process, immune-mediated, septisemia amongst others. The size of the dog does matter. Hip Dysplasia is more common in large dogs while cruciate ailments of the knee joint (stifle) are more commonly seen in small dogs. Obesity is another predisposing factor in developing arthritis. Excess weight over time puts tremendous forces on the majority of joints in the animals body.