Osteoarthritis (OA) is defined by clinical symptoms and radiological signs. Cartilage is crucial in the development, but all tissue components in and around the joint are affected by the disease. OA aetiopathogenesis is multifactorial and may be primary (idiopathic) or secondary, with an influence of heritable factors. Contributing to OA development are age, joint trauma, other joint diseases, and overweight/obesity. The latter is of special interest being modifiable, and weight loss has proven very effective on symptoms of OA. Over the course of OA, inflammatory flares may be experienced, some associated with crystal formation in the joint, which opens for possible treatments, as argued in this review.