'Osteoarthritis (OA) is a chronic condition which requires careful staging and monitoring once it is identified. OA causes chronic pain and, over the last 20 years, great progress has been made in understanding how pain is mediated in arthritic synovial joints. We know that the synovium is an important tissue and we have known for a long time that prostaglandins are an important target. However, the role of nerve growth factor (NGF) in the transmission of nociception in joints has become very clear in the last two decades. Many studies demonstrate that the binding of NGF to the TrkA receptor on the nociceptor causes internalisation of the NGF-TrkA complex. This leads to a cascade of events at the nerve ending but also in the cell body which leads to transcriptional changes which alter sensitivity and expression of neurotransmitters. Accordingly, we see peripheral and central sensitivity. This presentation will explain the pathophysiology of the evolution of pain in joints with OA and how NGF is central to this. The ability to block the action of NGF is a new way to manage the pain of OA in dogs and cats, and all small animal vets should have an understanding of the scientific basis behind this innovation.'