Osteoarthritis is quite literally 'wear and repair' within a joint. At the end of the bone, there is a layer of articular cartilage that stops the bone from becoming damaged and produces synovial fluid to lubricate the joint. In osteoarthritis, as the cartilage becomes damaged, the joint tries to repair itself by producing bony growths that cause inflammation within the joint. These changes can be due to age or previous traumatic damage to the joint.
With osteoarthritis, your dog will be stiff after a period of inactivity and may develop a limp or may even lick a particular joint. With any of these symptoms, you should take your dog to the vet as a diagnosis is important. An arthritic dog will generally slow down and become grumpier.
There is no cure for osteoarthritis but if your dog has it, medication could help relieve symptoms. The symptoms of osteoathritis are worse in dogs that are overweight or unfit and your vet could help you with advice on both losing weight and getting your dog more active if this is the case.